1
Stochasticity and Uncertainty
Experimentally Investigating Preference (In)Consistency in Two-Stage Decision
Problems
Abstract
We report on an experimental investigation into four prominent theoretical models of
two-stage decision-making, in which the decision maker (DM) makes a choice of a
menu in the first stage and then makes a choice from the chosen menu in the second
stage. Each of these models axiomatically derives a preference functional dictating
choice of the menu; some of them explicitly also specify choice at the from stage. Our
experiment uses lotteries as the final objects of choice, and we describe preferences
by the degree of risk aversion. We examine the goodness-of-fit of the four models in
explaining the choice of the menu, and the goodness-of-fit in explaining the choice
from the menu for the two of the four models who explicitly model the second-stage
choice. Our results indicate that our subjects’ behaviour is best explained by a random
indulgence model.
Keywords: two-stage decision problems, choosing a menu, choosing from the menu,
commitment, temptation, self-control, changing preferences
Lihui Lin and John Hey,
Department of Economics, University of York, Heslington, York, YO10 5DD.
Lin: [email protected]; Hey: [email protected]
Acknowledgements: We are grateful to the Leverhulme Trust for generously funding
this research with Leverhulme Emeritus Grant EM-2019-026/7
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1. Introduction
A common decision scenario in life is that of making a menu choice, and then a choice
from the chosen menu, such as choosing a restaurant and choosing food from this
restaurant; choosing an insurance provider and choosing one scheme from this
provider; and so on. A menu can be interpreted either literally or as an action
concerning an opportunity set that will affect subsequent opportunities. In this context,
dynamic (in-)consistency across the two stages will determine what decision makers
do.
This two-stage decision problem has recently been widely addressed in economic and
decision theory research. One of the most popular classes of models is that of Gul and
Pesendorfer (2001) (henceforth GP). This is termed a “self-control and temptation
model” which incorporates ex-ante preference, commitment demand and self-control
to resist temptation, to account for any dynamic inconsistency. GP model two types of
decision-makers – henceforth DMs – (namely, ‘self-control’ and ‘temptation
overwhelming’) .The widely discussed GP’s self-control model characterises a DM who
experiences temptation at the moment of choice from a menu and who anticipates
this in the first stage, where she1 selects which menu to face. In this first stage, the DM
has a particular perspective on what she should choose from menus, embodied in a
“normative preference”. The DM understands that her choice from menus will not
necessarily respect the normative preference, but rather will seek to balance her
normative preference with the cost of resisting temptation or giving in to the
temptation. Accordingly, the self-control DM may dislike a larger choice set since it
may include tempting choices, which are not desirable from the earlier perspective.
1 For ‘she’ read ‘he or she’ throughout and similarly for ‘her’, mutatis mutandis.
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There are other models following this line but adopting different perspectives. GP
suggests that not only the actual utility will matter, but that the existence of tempting
problems will lower utility. In this information-explosion era, available choices are
many, thus we usually will be exposed to many problems that may conflict with our
long-term normative preferences. A generalization of GP, Stovall (2010), (henceforth
Stovall), considers a situation where DMs are tempted by multiple temptations, and
hence incur higher costs to resist more temptations when temptation preferences are
uncertain. Another generalization of GP in terms of uncertainty is Chatterjee and
Krishna (2000) (henceforth CK). While Stovall and GP both include a cost of self-control
when the DM excludes possible temptations. CK addresses a cost of from the risk of
succumbing, that is, from ‘random indulgence’ rather than costly self-control: the DM
implements a dual-self-evaluation – the long-term normative preference and the
temptation driven preference – incorporating the fact that the individual considers the
possibilities of both selves.
Some argue that ignoring the future choice when taking the initial choice is not
necessarily optimal when new information regarding preferences or other variables is
expected to arrive in the future (Amador and Werning, 2005), since future preferences
may be uncertain in many cases. The literature interprets this anticipation of uncertain
future tastes as a preference for flexibility (Kreps, 1979). In this information-overload
era, the existence of many possible choices may distract attention and consequently
increase preference uncertainty. Flexibility models suggest that a larger set with a
range of possible future preferences will be preferred; this conclusion is opposite to
that of GP. For example, one of the flexibility models in the same two-stage decision-
making context is Ahn and Sarver (2013) (henceforth AS)’s model which incorporates
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preference flexibility and random utility theory. They model a DM who is uncertain
about her future preferences and anticipates the probabilities of each choice she will
make in the future and how much utility these choices will provide. The DM
correspondingly evaluates menus in the first stage according to these correct
predictions. In the second stage, one subjective state will be realised, and DM will
maximise the utility given this state. The key feature of self-control (as distinct from
flexibility) is the desire to keep commitment and eliminate possible temptations. The
price of flexibility is the cost of thinking (Ortoleva, 2013), such as keeping concentrated
or rational in a distracting context; while avoiding the existence of temptation could
reduce the distraction and temptation even though the cost of self-control and
opportunity should be incorporated.
Given the difference between these various models, several questions arise. The main
purpose of this paper is to report on an experimental test of the above-mentioned
models and understand how ex-ante preference translates into the choice of a menu
and the subsequent choice from the chosen menu in a reasonably general context.
Investigating the choice patterns in this context and assessing the quantitative strength
of commitment, temptation and flexibility preference across choices offers insights
into how decision-makers view and consider temptation, and thus how policy makers
may eliminate or manipulate the temptation. In this information-explosion era,
available choices are many, and marketeers use elaborate marketing schemes, such as
nudging, anchoring, discount and bundling, to tempt consumers. In most daily
scenarios, the existence of other choices is a source of temptation, which will distract
and may overwhelm attention and willpower; subsequently the compulsive desire to
engage in short-term urges for enjoyment conflicts with long-term goals. Normally,
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some unexpected possibilities might look good for some reasons in particular contexts.
Students who want to study on their own, if there are mobile calls or distracting
sounds, find it easy to change their choices. People who want to have saving plans can
easily change their decision if they go to a mall with large discounts. An investor who
has suffered multiple investment failures may decide to make a more risk-averse
portfolio ̶ however, she may be persuaded to choose a particularly high-return gamble
when the investment manager offers such options. Thus, as we will discuss later when
we describe our experimental design, we introduce temptation by inserting both very
safe, and very risky lotteries, into the menu to distract choices. Thus, by “temptation”
and “self-control” in our case, we applied Dekel, et al (2009)’s definition: “we mean
that the agent has some current view of what actions she would like to choose, but
knows that at the time these choices are to be made, she will be pulled by conflicting
desires.” We refer to temptations as problems extremely different from ex-ante and
planned-to-implement preferences. However, we should note that the motive of self-
control is not our main interest. Most decisions of our daily life do not always involve
right-and-wrong questions, but the conflict between long-term desire and current
tempting desires may lead to negative feelings. We focus on measuring how actual
choice deviates from ex-ante preference by the intervention of temptation. Ex-ante
preference and commitment are valuable for ex-ante surveys, such as polls, consumer
preference surveys, saving and consumption plans, which are considered by policy
makers and business decision makers. Furthermore, the choice of menu is a set of
chosen opportunities for the future final consumption. It is meaningful for future
market prediction.
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Despite the obvious importance of the topic, as illustrated above, it is difficult for
empirical research to investigate ex-ante commitment preference, temptation
preference and flexibility preference in one context. This has been partly done by
Toussaert (2018) who designed an experiment to test GP focusing on the self-control
type identification. Her experiment implements the temptation by offering additional
earnings to read a sensational story during a tedious attention task for which subjects
received payment. In our paper, we report on a more general experiment which tests
and compares these four models. Our experiment generalises the environment in
order to carry out parametric estimation and an assessment of the relative explanatory
abilities of the different models.
We follow the theoretical models’ use of menus as sets of lotteries, and lotteries will
be used to infer risk preferences. Our experiment involves a three-step procedure to
infer the commitment preference, temptation preference and flexibility preference.
First, we elicit the subjects’ ex-ante preference (singleton evaluations of lotteries)
using (our slight modification of) Holt-and-Laury’s price list method and hence infer
the ranking of singleton menus. Second, subjects were asked to choose one menu from
a set of menus; and third, choose an option from the chosen menu. Importantly, we
give different subjects different menus according to their ex-ante risk preferences; this
embodies the idea of a personalised offering based on an ex-ante market survey (as
current online shopping websites do). We implement the temptation by offering
certainty choices, very low-risk choices (a high probability of getting a low payoff) and
very high-risk choices (a low probability of getting a high payoff). In addition, to
implement the flexibility, the size of the menus varies. Menusets are designed carefully
to promote the tradeoff between the cost of self-control and the opportunity cost:
details are given in the experimental design section.
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We should note that there is a large literature in psychology and decision science,
which has discussed self-control, commitment and flexibility demand, willpower and
temptation. Toussaert (2018) and Dean and McNeill (2015) experimentally explore the
GP and AS models and study commitment and flexibility, but our design is different.
We generalise the temptation trying to reflect our most daily decision scenarios – not
strictly right or wrong/good or bad decisions. To our knowledge, we are the first to
conduct parametric estimation and qualitatively measure the different preferences,
that is, ex-ante preference, and temptation (ex post) preference. Crucially, the
importance of menu choice research is that the chosen menu determines the
subsequent opportunity set and hence the final decision or consumption. While most
research in this field focus on the choice of menu stage, we go one step further by
examining also the choice from the chosen menu to test the predictive power of
models and behavior consistency. Believing that economics is all about predicting,
rather than just explaining, we compare four of our models by seeing how good they
are at predicting choice from the menu, that is, final consumption. However, with our
data, we only can test the predictive power of the from stage in GP and CK models (this
is because we cannot observe the realized preference in each decision or have enough
observations to fit the from stage of the Stovall and AS models). We elaborate on this
point in section 2.
This paper is organised as follows. Section 2 introduces the models. Section 3
compares and contrasts them, using a motivating example. Section 4 describes the
experimental design and section 5 the econometric specification. Section 6 discusses
and interprets the results. Section 7 concludes with a summary of the results, a
discussion of findings and implications
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2. Models and a motivating example
The motivation for the model comparisons is based on the distinctions between the
different two-stage decision making models. This section discusses the models that we
investigate, and describes how flexibility preference, self-control and temptation
influence the decision making over menus and the corresponding implied choice from
the chosen menu. While Stovall and CK only address the choice of menu stage, we
extend these models into two stage models induced from the of stage. We also justify
why we have difficulty in predicting and estimating the from stage of AS and Stovall
with our experimental data.
We pay particular attention to preference functionals in terms of ex-ante preference u
(that is the preference over singleton lotteries), the menu preference U, and the ex-
post preference v (that is, the temptation preference)2. We present the behavioural
representations and intuitions. We do not explore the theorems and axioms, leaving
that to the original papers.
2.1 Self-control and temptation in GP 2001
This paper studies a two- stage model where ex-ante inferior choice may tempt the
decision-maker in the second stage. Individuals have preferences over sets of
alternatives that represent second stage choices. Their axioms yield a representation
that identifies the individual’s commitment ranking over singletons (that is, ex-ante
preference u), temptation ranking (that is, ex post temptation preference v), and the
2 Both u and v are von Neumann-Morgenstern utility functions over lotteries.
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cost of self-control. An agent has self-control (self-control subject) if she resists
temptation and chooses an option with a higher ex-ante utility. The paper also models
another type of agent (temptation overwhelming subject) who is overwhelmed by the
temptations and gives in to them.
The preference functional for the choice of menu in GP is given by
For a self-control DM (henceforth GP type 1)
( ) max ( ) ( ) max ( )U A u x v x v y where ,x y A (1)
For a temptation-overwhelmed DM (henceforth GP type 2)
( ) max ( ) subject to ( ) ( ) for all U A u x v x v y y A , where ,x y A (2)
Here A is a menu of lotteries and ,x y A . For a self-control DM, GP interprets
max[ ( ) ( )]v y v x as the cost of self-control. Since the cost is always positive, the
existence of temptation in the menu will decrease the utility of the menu. Thus, the
self-control DM may anticipate the temptation and will tend to avoid the temptations
in the menu. This suggests that a smaller menu size without temptation will always be
preferred. At the choice from menu stage, they suggest an optimal compromise
between the utility of commitment preference u and the temptation preference v by
maximizing u+v. However, self-control is a limited mental resource. When the cost of
self-control is too high, the DM might end up with giving into the temptation. So, for
the temptation-overwhelmed DM, she values more the temptation and thus
maximises the temptation utility v first then evaluates these choices based on the
commitment preference u. After choosing the menu, a temptation-overwhelmed DM
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gives in to the temptation by choosing the lottery with the maximum temptation utility
from the chosen menu.
2.2 Multiple temptations in Stovall
This model generalises GP by considering a decision maker who is tempted by multiple
normatively (ex-ante) worst alternatives. At the same time, she would want to expand
her choice set by including normatively superior alternatives. As Stovall argues, in the
choice of menu stage the DM is not tempted by any alternatives but just predicts the
possible state at the time of choosing from the menu. Put simply, the DM anticipates
the future possible temptations and maximises the maximum expected utility her
present self can obtain by choosing among the realised future self’s most preferred
lotteries in the menu. A DM wants to choose a menu of opportunity sets for a future
period of time so as to maximise the utility of the menu as evaluated as the present
moment. However, she is uncertain what will tempt her in the future, so all the
possible temptations will be considered. The model suggests that the agent is
uncertain which of these temptations will affect her.
The preference from menu functional for Stovall is
1
( ) {max ( ) ( ) max ( )}s
s s ss
U A q u x v x v y
where ,x y A (3)
Here s S is the subjective state. There are multiple temptations and sq is the
probability of being tempted by temptation ( )sv y . In state s, ( )sv y is the temptation
that affects the agent. Similar to GP, the DM compromises between the normative
preference and temptation preference and chooses the alternative that maximises
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su v conditional on the subjective state s . Meanwhile, the DM experiences the
disutility of self-control, which is the foregone utility from the most tempting
alternative. The model suggests that the DM is uncertain which of the temptations will
affect her. This model implies that adding a normatively superior option into any menu
will increase the utility of the menu while adding a temptation into the menu will make
the menu less desirable. The DM evaluates the menu by trading off the normatively
superior option and anticipating possible temptations. This model shares the same
spirit of GP’s self-control. A menu with more temptations will be avoided by exerting
self-control; thus, a smaller size of menu will be preferred.
Stovall does not model the choice from the menu stage3. His model is a generalisation
of GP (called ‘random GP’) and is a special case of Dekel et al (2001)’s model. According
to the justification of Dekel And Lipman (2012), a random GP representation
generalizes the notion of a GP representation in a fashion exactly analogous to the GP
with the maximiser of u v from the menu, given the probability sq ; specifically, the
u is fixed, but there is an anticipated probability measure over the “temptations” ,
while at the final stage, the preference uncertainty will be resolved, that is, one state
will be realized.
2.3 Stochastic Temptation in CK
3 He writes (page 350): “It is understood, though unmodeled, that she will later choose an alternative from the
menu she chooses now.”
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GP and Stovall are grounded on the conflict between ex-ante normative preference
and ex-post temptation preference. There is another perspective to model the conflict
and the consistency between preferences. CK models them by a dual self with a
stochastic story. Differing from using strong self-control to avoid the existence of
temptation, DMs are modelled as considering the possibility of being tempted in the
future rather than excluding all possibilities with cost of self-control at the first stage.
This model interprets temptation as a systemic mistake in which the second-stage
choice could be interpreted as being made by an “alter ego” who appears randomly:
DMs at the first stage consider the probabilities to be tempted at the second stage.
The choice of menu preference functional of CK is
( )( ) (1 )max ( ) max ( ) where ( ) is the set of maximisers in vx A y B A vU A q u x q u y B A v A
(4)
where q is the probability of being tempted. CK refer to their model as a dual-self
model, where u is the utility function of the long run self and v is the utility function
of the other self. When making the choice of menu, the DM believes she has q
probability that the other self will dominate at the choice from the menu stage; that
is, giving into the temptation. Following the spirit of self-control, the representation
could be interpreted as an internal battle for self-control with the alter ego where q is
the probability to lose self-control.
As noted above, the choice from the menu stage is unmodeled in CK. However, it
seems reasonable to follow the decision rules implicit in CK’s discussion: “a decision
maker who satisfies our axioms behaves as if there is a probability of her being
tempted when a choice has to be made from a menu, which is represented as the
choice being made by an alter ego. It should be emphasised that the alter ego (and his
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utility function v) is subjective, as is the probability, q of getting tempted.” Thus, two
selves, that is, self-control or giving into temptation, one will stochastically dominate
at the choice from menu stage given the probability q, (q is the probability to choose
the maximum v, and 1-q the probability to choose the maximum u from the chosen
menu).
2.4 Preference Flexibility and Random Choice in AS
In marked contrast with the self-control and temptation stories, AS considers a story
where ex-ante preference (commitment in GP) does not play a role in the first stage
choice due to the preference uncertainty. Thus, there are no conflicts between the
normative preference and the temptation preference. They suggest a two-stage model
incorporating the preference flexibility of DLR and the random choice of Gul and
Pesendorfer (2006). They model a DM who is uncertain about her future preferences
and anticipates the probabilities of each choice she will make in future and how much
utility these choices will provide. The DM evaluates menus in the first stage according
to these correct predictions4. In the second stage, one subjective state will be realised
(which is a random draw from the belief distribution at the first stage), and the DM will
maximise utility given this state.
The preference of menu functional for AS is
( ) ( )max ( )sU A q s v x where x A (5)
4 Their model proposed the condition of correct belief on future preference contingency. But it does not guarantee the belief will be necessarily correct in reality. We also tested this in our experiment.
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Where s S is the subjective state and the 'q s are the probabilities of anticipated
future preferences. So, the utility of a menu A is equal to the expected utility of the
best option in A, with expectations taken over the different possible utility functions
indexed by the state S, which we refer to as the belief about the preferences at the
second stage. This model suggests that the DM will prefer flexible menus, which offer
many possible future choices. A simple case is that we might be unsure whether we
would like to have cheesecake or scone before we actually go to the restaurant. Thus,
simply choosing the restaurant that offer everything will be easier way. As for the
choice from the menu, AS suggests that the DM maximises the utility given the realised
state. So, we will know which we actually want to choose when we go to the restaurant
and make the final decision.
3. Connections and Differences between the Models
The four models we are investigating describe behaviour in our two-stage setting from
different perspectives. For example, you want to buy a new computer. You also have a
saving plan to consider. Your ex-ante normative preference are the cheaper the better.
However, once you start searching online you may be persuaded otherwise by
discounted offers, PC reviews or overall popularity. In this scenario, we may consider
3 options:
A) a website that only offers cheap computers {a, b};
B) a site that offers several popular but more expensive brands {c, d};
C) Offers all of the above {a, b, c, d}.
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Suppose your preferences are as follows: ( ) ( ) ( ) ( )u a u b u c u d and
( ) ( ) ( ) ( )v a v b v c v d .
A costly self-control GP DM will avoid the existence of temptation by choosing the
smallest size of menu, that is, the website A with only cheap computers because she
wants to avoid the potential risk to lose control and change her original purchase plan.
A temptation-overwhelmed GP, thinks that she may give in to the temptation ̶
evaluating the menus by the ex-ante utility of the most tempting. Thus, menu A is
evaluated as u(b); menu B is evaluated as u(d) and menu C as u(d). Thus, website A is
preferred. If she is uncertain about the temptation, she would be a Stovall DM who
considers the possibilities to give in to each temptation and avoids all possible
temptations, that is the possibilities to be tempted by d, c and b. Clearly, the website
A will be still preferred. Similarly, a CK DM also considers the possibilities to be tempted,
but only considers the most tempting one, that is b in menu A, d in the menu B and d
in the menu C (since she evaluates succumbing to temptation by the ex-ante
preference); thus a CK subject also will choose website A. We see that GP, Stovall and
CK suggest the same choice of menu.
However, an AS DM enjoys the larger choice set in the presence of uncertainty and
forgets her ex-ante money-saving plan and browses the websites at random. The
flexibility will provide an easier way to choose the menu where opportunity costs do
not exist. All the possibilities will be taken into consideration. The menu that contains
more possibilities will be preferred, that is website C.
In summary, each model implies a particular preference functional. Some of them lead
to the same choice of menu, while different final decisions from the menu. We can see
that they also have connections. GP and Stovall postulate the motives of self-control
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and disutility of temptation. Stovall is a generalisation of GP. Stovall and AS address
uncertainty and flexibility. However, flexibility and possibility play different roles in
Stovall and AS. CK is a generalisation of GP Type 2. GP, Stovall and CK can be
interpreted as multiple-self stories. In these models, present-biased subjects may
demand the commitment devices to constrain the choices of the future selves if they
expect to succumb to temptation while addressing the conflicts between the tempted
self and the ex-ante long term self. While AS does address this, AS does not suggest
excluding possibilities as do GP and Stovall. On the other hand, CK could be a special
case of AS, when ex-ante preference is the temptation preference and there is only
one possibility.
Our experiment is designed to investigate these differences and connections.
3.1 Whether the strength of ex-ante preference or preference flexibility is prevalent
in reality
GP, Stovall and CK are dependent on the conflict between ex-ante normative
preference and ex-post temptation preference(s). The DM has to exert self-control to
resist this conflict. In contrast, AS addresses a preference for flexibility where ex-ante
preference do not impinge on subsequent decisions. Consider three menus {a}, {b},
{a,b} with preferences u(a)>u(b) and v(a)<v(b). Then GP, CK and Stovall would imply
{a} > {a, b} > {b}. However, AS would suggest {a,b} will be preferred over {a} and {b}.
This is what is generally referred to as ‘Preference for Flexibility’, and it results in
preference for a larger menu set. It is this property, which distinguishes the preference
uncertainty models from models of temptation and self-control in which smaller
choice sets may be preferred to avoid exposure to tempting problems.
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3.2 Whether adding middle level problems influences the utility of a menu?
While AS and Stovall assume preference uncertainty, they refer to the choice of menu
stage as a future anticipation stage because the DM considers future possibilities. AS
includes all possibilities while Stovall avoids all possibilities of temptation. To some
extent, AS could be regarded as a special case of Stovall when the ex-ante normative
preference is the same as the ex-post temptation preference (that is, where preference
conflicts do not exist). But GP and CK evaluate the menus concentrating on two
problems with maximum temptation and maximum ex-ante preference. Consider
three menus {a}, {b}, {a, b} with preferences u(a)>u(b) and v(a)<v(b). Now add an extra
choice c, which is between a and b in terms of preference (both ex-ante and ex post),
that is, u(a) > u(c) > u(b) and v(a) < v(c) < v(b). When c is added to the menu, so that it
becomes {a,b,c}, AS implies that the menu will become more attractive as long as c has
positive probability to be chosen in the future, while for Stovall, the menu will become
less attractive. However, the utilities of the menus will not change for GP and CK.
3.3 Which induced choice from menu from each model can better fit the data?
As Dekel and Lipman (2012) conclude, different subsequent choices from menus can
be deduced from the choice of menu behaviour. This is important since GP, Stovall, and
CK identify the same choice of menu. The importance of choice of menu research is
the predictive power of future choice from the menu, as it implies the final choice.
Unfortunately, we cannot test the predictive power of AS and Stovall using the data
from our experiment. As already mentioned, the DM has preference uncertainty in AS
and Stovall at the of stage; and a preference will be realized at the from stage according
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to a particular random rule. The final decision will be determined by a particular
realized preference. In our experiment, we only can observe the final choice from the
chosen menu but cannot observe the realized preference in each final decision. To
precisely predict and estimate the from stage of AS and Stovall, would require the
repetition of each task a considerable of times.
4. Experimental Design
4.1 Lotteries
Following the theoretical literature, we used lotteries5 as the items/problems being
eventually chosen and experienced. We chose particularly simple lotteries, consisting
of just two possible outcomes: a high payoff, which we denote by x and a low outcome,
denoted by y. We denote the probability of x by p. A typical lottery, as portrayed in the
experiment is shown in the figure below.
5 Using other objects, such as goods creates problems as we would need to be able to elicit their preferences over such objects. Lotteries are relatively simple as we can measure preferences by risk attitude.
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Figure 1: a typical lottery
The vertical axis represents the payoff and the horizontal axis the probability. So, the
lottery shown in the figure above has a 30% chance of resulting in a payment of £6 and
a 70% chance of resulting in a payment of £13. The red area represents the low payoff
and the blue the high payoff. One possible advantage of this representation, as
compared with others in the literature, is that the total area indicates the expected
payoff of the lottery.
We employed a total of 27 lotteries. These were chosen carefully, so as to give a range
of lotteries, from those attractive to risk-averse subjects to those attractive to risk-
loving subjects (we do not know their risk-aversion ex-ante). We constructed these as
follows: we started with lottery number 1, a certainty of £10. Then we constructed the
other 26 lotteries sequentially using indifference. Details of the lotteries design see
the online appendix A.
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The experiment was designed in two parts. Part 1 elicited their ex-ante evaluation of
singleton lotteries by using (our slight modification of) Holt-and-Laury’s price list
method. From this, we can infer the ranking of singleton menus (that is, those
consisting of just one lottery). Part 2 consisted of two stages: first, subjects were asked
to choose one menu from three different menusets (sets of menus) of different sizes
and composition; second, they were asked to choose one lottery from the chosen
menu. Part 1 consisted of 27 tasks, and Part 2 consisted of 30 tasks. Note that the
menus and menusets in part 2 varied across subjects according to their evaluation of
the singletons in part 1. At the end of the experiment, one of the total of 57 tasks was
chosen at random, and the subject’s decision on that task was ‘played out’. Following
all models’ original menus as sets of lotteries, lotteries will be used to infer the risk
preference, and hence determine the preferences as defined in each model.
4.2 Eliciting the ex-ante preference on temptation free singleton lotteries
The evaluation of the ex-ante preference, which is a key component in most models
under consideration, cannot be observed from the two choices (choice of a menu and
choice from the menu) in the second part of the experiment. Thus, we elicited the ex-
ante risk attitude ur in the first part using (our slight modification of) the Holt and Laury
price-list mechanism. In this first part, we asked subjects to value each lottery:
subjects were told to imagine that they owned the lottery and planned to sell it; their
valuation is the smallest amount of money they would happily accept to sell it.
Alternatively, they were asked to imagine that they did not own the lottery and were
thinking of buying it; then the valuation is the largest amount of money they would
happily pay to buy it. Thus, their valuation depends on their own ex-ante risk attitudes.
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This elicitation came before the subjects began to make decisions in Part 2 of the
experiment. In Part 1, we elicited each singleton valuation by showing a particular
lottery on the left of the screen and a drop-down list of numbers on the right. Subjects
indicated their valuation of the lottery on the left by ticking one of the numbers on the
right. The Instructions showed the interface; it is given in Appendix Figure 1.
To provide them with an incentive to reveal the true evaluation, we used the following
method to pay subjects if one of these lotteries was played out at the end of the
experiment: we randomly selected one of the numbers from the drop-down list; if that
number was less than the number they had ticked, we played out the lottery on the
left; if that number was equal to or greater than the number they had ticked, the
payment was the number that they have ticked.
4.3 Menu and temptation design
The implement of temptation was designed carefully. Temptation is a taste shock
where the individual’s future desire conflicts with their initial desire. We would like to
generalise the temptation as the existence of diverse and extremely different
problems that conflict with our initial preference. In our daily life, what distracts us
and motives us to change our preference is not always something strictly bad or wrong
in this information-exploration and choice-overload era. For example, we may have
impulsive shopping behaviour that we do not plan to do when we are seeing
something beautiful in a shop window. We may plan to have a risk neutral investment
portfolio, but we may be attracted by a high possible outcome to become more risk-
loving if the investment adviser offers a risky portfolio. Thus, in our experiment, we
designed some extremely safe and extremely risky problems as source of temptation.
22
As we have inferred the ex-ante preference ru the first stage, our experimental
software generated the menus accordingly. Thus, we designed the menus within each
menuset with different degrees of riskiness that deviate from their ex-ante risk
aversion. For example, each menu will have one or two lotteries close to subjects’ ex-
ante preference, that is, those that have an expected utility close to their maximum
expected utility given their ru; while some menus will have different lotteries with
different degrees of risk, which were usually extremely risky or safe problems
compared with their most ex-ante preferred lotteries.
4.4 Menusets
The menusets were carefully designed. Each menuset had three menus with different
sizes (to implement the flexibility and multiple temptations) – one menu had two
lotteries without temptations and these two lotteries which had close to the maximum
utility given by their ru; one menu had three lotteries with two ex-ante preferred
lotteries given their ru and one possibly tempting lottery; one menu had four lotteries
with two ex-ante preferred lotteries given their ru and two possibly tempting lotteries.
To incentivise subjects to trade off and evaluate the menus carefully, the menus did
not fully overlap each other: If the larger menus contain the lotteries of smaller menus,
subject may simply choose the larger size without thinking and decide the final
decision carefully at the last stage. So the temptation-free menu has the most
preferred lotteries given their ru; the larger menus with temptations have less
preferred lotteries given their ru.
Let us give an example. Suppose the estimated risk-aversion, ru, of a particular subject
is 0.32. Using the notation xpy to denote a lottery which leads to a payoff x with
23
probability p and to a payoff y with probability 1-p, then the lotteries 180.3697, 200.2538
and 180.4306 are closest to the subject’s ex-ante preferences; these are lotteries 14, 15
and 13 respectively (see Appendix Table 1 and Figure 2 above). We constructed a
menuset containing the menus below
A 14 15
B 14 13 1
C 15 13 1 27
Lottery 1 is the safest lottery and lottery 27 the riskiest; these are the furthest away
from the subject’s ex-ante preferences, and hence possibly the most tempting.
Meanwhile lotteries 13, 14 and 15 are the least tempting. Menusets were constructed
subject-by-subject using this design.
5. Stochastic Specification
The choice of menu stage in all models are deterministic stories, identifying a
particular optimal menu. In any experiment, however, there is behavioural noise:
subjects often choose differently when offered the same choice on several occasions.
This fact implies that we have to model choices of menus in a stochastic fashion;
otherwise no model can explain the data. The multinomial logit model (or Luce model)
is perhaps the most commonly used model of discrete choice to account for
behavioural stochasticity. With this model, behaviour does not behave in a fully
random way but follows a particular random pattern. According to this model, the DM
evaluates the problems with some noise. If the noise in the evaluation is additively
separable and independently distributed according to the extreme value distribution,
then the multinomial logit model emerges. We use Luce’s random model to add
experimental noise into the choice of menu models. This model assumes that
24
the probability of selecting one menu over another from a set of many menus is not
affected by the presence or absence of other menus in the same context. The choice
probability formula is given by the equation below.
i
j
U
i U
j
eP
e
Where Ui is the expected utility of menu i, j is any other menu in the menuset and λ
is a precision parameter which measures the amount of experimental noise, and
reflects the variance of the unobserved portion of utility.
Ui is determined by different parameters in each model (our parameters of interest).
The choice of menu in GP and CK is determined by the ex-ante preference u and the
temption preference v in the menu; thus ru and rv are our estimated parameters in GP
and CK. In Stovall and AS, each DM is postulated to have a belief about her or future
preferences with corresponding probabilities. We could not estimate each single
possible preference and the discrete probability; the parameters will be too many to
be identified6. To make the likelihood function more parsimonious, we instead assume
that the belief on temptation preference can be modelled by a continuous normal
distribution with mean μ and standard deviation σ. We estimate μ and σ in AS and
Stovall.
5.1 Model identifiability demonstrated through simulation
6 For example, each menu set has 5 lotteries allocated in different menus. If we estimate the preference of each single lottery, and the corresponding probability, we will need to estimate at least 10 parameters, and a precision parameter, which gives 11 in total.
25
As already discussed, GP, Stovall, and CK identify the same choice of menu in some
cases, and hence they may not be distinguishable. We demonstrate identifiability with
our Luce stochastic specification7 through a simulation.
In this simulation we have assumed that ru=0.32 and have used the corresponding
menusets generated as in our experiment as described above. We first generated
10000 sets of observations on the choice of a menu for the different models assuming
Luce noise. We then estimated the parameters of the different models. This was to see
if the maximum likelihood estimation can identify the true model that was used to
generate the decisions, and if the true parameters can be estimated. We use the BIC8
criterion to determine the best-fitting model. The results are in Tables 3 to 7.
Table 3: True Model is GP type 1
True Model is GP type 1 with parameters 1.7rv and 800
Mean estimated parameters are 1.698rv and 802.778
Estimated model
GP type 1 GP type 2 CK Stovall AS
Mean uncorrected log-
likelihood -139530 -145893 -144387 -150698 -329634
BIC 279084 291812 288811 301434 659274
7 Of course, this assumes that our subjects are noisy in their responses. 8 BIC is the Bayesian Information Criterion; this corrects the log-likelihood for the number of parameters.
26
Table 4: True Model is GP type 2
True Model is GP type 2 with parameters 1.7rv and 800
Mean estimated parameters are 1.888rv and 800.17
Estimated model
GP type 1 GP type 2 CK9 Stovall AS
Mean uncorrected log-
likelihood -107150 -106183 -106183 -119592 -329584
BIC 123949 122219 122232 321434 623274
Table 5: True Model is CK.
True Model is CK with parameters 1.7rv , 0.8q and 800 .
Mean estimated parameters are 1.83rv , 0.80q and 803
Estimated model
GP type 1 GP type 2 CK Stovall AS
Mean uncorrected likelihood -259048 -259300 -247961 -257452 -274653
BIC 518121 518625 495960 514941 549344
9 When the probability to be tempted is 1 in CK, the CK representation will become GP type 2. Thus, the likelihood of CK is the same as GP type 2 and estimated probability is 1. Note that the BIC of two models are different thus,we still can
identify the true model according to the lowest BIC
27
Table 6: True Model is Stovall
True Model is Stovall with parameters 1.2 , 10 and 800
Mean estimated parameters are 1.24 , 11.00 and 828.24 .
Estimated model
GP type 1 GP type 2 CK Stovall AS
Mean uncorrected likelihood -255119 -300144 -253231 -231355 -274670
BIC 510264 606314 506498 462747 549378
Table 7: True Model is AS
True model is AS with parameters 1.2 , 10 and 800 .
Mean estimated parameters are 1.19 , 12.81 and 789.22 .
Estimated model
GP type 1 GP type 2 CK Stovall AS
Mean uncorrected likelihood -327949 -329335 -329574 -329169 -308255
BIC 655923 658695 659185 658375 616548
The above tables show that using the Luce model, GP, CK, and Stovall are
distinguishable and identifiable. Obviously, AS is easily to be distinguished as it is
opposite to the other models.
28
5.2 Simulation of prediction
As mentioned, we also want to test the models’ predictive power to see which model’s
choice of menu stage better implies the choice from menu, and hence whether our
subjects were consistent. So we used the estimated parameters of the of stage to
predict behavior at the from stage, and compared the corresponding prediction log-
likelihoods. Our hypothesis is, that, if DMs are consistent across stages according to
the models, the model that fits the behavior at the choice of menu stage, should also
predict best the choice from menu stage given the same parameters. We report here
a simulation to test this hypothesis (which we will use in the results section). As we
have already noted, we cannot estimate AS and Stovall in our experiment due to the
limited number of observations, so only results for GP and CK are reported here.
Table 8: True Model is GP type 1
True Model is GP type 1 with parameters 1.7rv and 800
Mean estimated parameters are 1.698rv and 802.778
Predicted models of from
GP type 1 GP type 2 CK
Mean uncorrected log-likelihood -67435 -97908 -119916
29
Table 9: True Model is GP type 2
True Model is GP type 2 with parameters 1.7rv and 800
Mean estimated parameters are 1.89rv and 799.14
Predicted models of from
GP type 1 GP type 2 CK
Mean uncorrected log-likelihood -50378 -43021 -44498
Table 10: True Model is CK
True Model is CK with parameters 1.7rv , 0.8q and 800 .
Mean estimated parameters are 1.83rv , 0.80q and 803
Predicted models of from
GP type 1 GP type 2 CK
Mean uncorrected log-likelihood -237088 -242278 -201484
Tables 8 to 10 show clearly that, if DMs are consistent in terms of preference, the true
model has the higher log-likelihood. Hence, the predictive powers can be compared
and the true generating model identified. We use this in our results section.
6. Results
In this section, we present the experimental results from the experiment conducted at
EXEC, the Centre for Experimental Economics at the University of York, in 2021. A total
30
of 82 subjects (mainly students) participated in the experiment10and mean earnings
were £23.50 per subject (including a £2.50 show-up fee).
6.1 Flexibility and temptation: some descriptive statistics
Overall, the frequency to choose size 2 menus (that is, menu 1) was 32%, the frequency
to choose size 3 menus (that is menu 2) was 22%, and that to choose size 4 menus
(menu 3) was 46%. In the temptation menu sets, the frequency to choose size 2 menus
(menu 1) was 27% ,the frequency to choose size 3 menus (menu 2) was 14% , and that
of size 4 (menu 3) was 59% (see Table 9).
Table 11: the frequency to choose each menu
Menusets type menu 1 menu 2 menu 3
temptation free menusets 0.32 0.22 0.46
(0.24) (0.19) (0.26)
temptation menusets 0.27 0.14 0.59
(0.19) (0.16) (0.25)
Each subject completed 30 tasks, each involving a choice of a menu and a choice from
the chosen menu. We start with some descriptive statistics. In order to test if subjects
are tempted by our designed temptations, we included in the menusets, 5 menusets
that contained temptation-free menus where there are no tempting lotteries.
Comparing average frequencies to choose different sizes of menus (see Table 11), we
can see that subjects had a relative higher tendency to choose the flexible menu where
10 Due to covid 19, we conducted our experiments online in our virtual lab.
31
there were temptations. Note that menu 2 has one temptation, while menu 3 has two
temptations.
We report in Table 12 on a regression of the choice frequencies across different
menuset contexts to see the relation between choice frequencies of different menus
and temptation (free) menu set. If our implementation of temptation worked, subjects
will have higher tendency to choose larger menus in temptation menusets than in
temptation-free menusets, and correspondingly higher tendency to choose smaller
menus in temptation-free menusets than temptation menusets. According to table 8,
the individual choice frequency of menu 3 in the temptation menu set is significantly
higher than that of temptation free menuset. Accordingly, the tendency to choose
menu 1 is significantly lower in temptation menusets than in the temptation-free
menu sets. These results show that our method to design the temptation do tempt
the subject to give into the menu with more temptations and choose flexibility. Our
conclusion from this descriptive data is that the way that we have designed our
menusets is valid.
32
Table 12 regression of the choice frequencies across different menusets
individual choice
frequency menu 1 menu 2 menu 3
-0.053* -0.082** 0.135**
(0.033) (0.272) (0.040)
Independent dummy variable: Temptation free menu
sets=0; Temptation menu sets=1. There are 82 observations
for each treatment.
Dependent variable is individual choice frequency of each
menu types, that is, the menu 1 with 2 options, menu 2 with
3 options, menu 3 with 4 options.
*p<0.1
* *p<0.05
6.2 Model comparisons
This section proceeds in two stages: first, we use the data from the choice of the menu
to fit and rank the models; we then use the fitted parameters from this estimation to
predict the data from the choice from the menu and once again fit and rank the models.
We start with the first stage.
We estimated, by Maximum Likelihood, each of the 4 choice of menu functionals for
the 82 subjects subject-by-subject, using the data on the choice of the menu, obtaining
estimates of the parameters of the functional and of (the precision), and, of course,
the maximised log-likelihood. We then used, for each subject and for each model the
estimated parameters to predict behaviour of choice from the menu given each model.
This gives us a prediction log-likelihood for each model and for each subject — this is,
33
of course, a measure of the predictive abilities of the models. We did this for GP and
CK, because these two models predict different choices from the menu even though
they indicate the same choice of menu. Doing so enables us to discriminate between
the two models.
We start with Table 13; this shows the mean and standard deviation (across all subjects)
of the fitted log-likelihoods. However, this table does not allow us to compare the
goodness of fit across preference functionals, for the simple reason that they have
different degrees of freedom (GP has 2 estimated parameters, CK 2, Stovall 3, and AS
3). If we correct the fitted log-likelihoods for the degrees of freedom by calculating the
Bayesian Information Criterion (BIC), we get the bottom half of Table 9; recall that the
lower the BIC the better. It seems to show that, on average, CK is the best, followed by
GP, and then AS and Stovall.
Table 13 (mean and standard deviation of maximised log-likelihoods and the values
of BIC)
GP11 AS CK Stovall
uncorrected likelihoods -30.58 -29.34 -23.52 -32.66
(4.53) (3.45) (7.73) (0.74)
BIC 69.35 70.96 55.23 77.61
(9.06) (6.90) (15.46) (1.47)
11 GP models two types of subjects, self-control and temptation overwhelming. We identify the type by the higher maximised likelihood since two types have the same number of parameters. 78.2% subjects are identified as self-control type and 21.8% are temptation overwhelming subjects.
34
We now look at individual subjects. If we rank the various functionals using the BIC,
we get table 14. Here we report all the observed rankings and their corresponding
frequencies. To interpret the table, we note that each row reports the frequency of
the subjects with that particular ranking. So, for example, 49% ranked CK first, then AS,
then GP, then Stovall. Overall, we note that 91% put CK first, and 9% GP first.
Table 14 Rankings based on the BIC and the frequencies of each ranking over all
subjects
1st 2nd 3rd 4th Frequencies
CK AS GP Stovall 0.49
CK GP AS Stovall 0.29
GP CK AS Stovall 0.06
CK GP Stovall AS 0.13
GP CK Stovall AS 0.03
We now test the relative statistical significance of our estimates using the Vuong test
(table 15). This tests, for each pair of models whether one fits significantly better than
the other. We see that CK is at the top of the rankings, followed by GP and AS, then
Stovall. Note that the Vuong test between GP and AS is not significant, which means
that they are equally close to the true model.
35
Table 15 significance tests of comparative model fit
H0: Model 1 and model 2 are equally close to the true model
H1: Model 1 is closer to the true model than model 2
model 1/model 2 GP AS CK Stovall
GP - 1.216 -4.101 8.267
AS -1.216 - -5.821 5.896
CK 4.101 5.821 - 6.812
Stovall -8.267 -5.896 -6.812 -
-has no meaning
If V> 1.96, model 1 is significantly better than model 2;
If V< -1.96 model 2 is significantly better than model 1;
If |V| < 1.96 model 1 and model 2 are equally close to true model.
6.3 The predictive power of each model
The above analyses are concerned with the explanatory ability of each model in the of
stage. Now we check the predictive power in the from stage for GP and CK12. As can be
seen from Table 15, GP and CK come out well in the fitting of the of stage. We now
want to see which of the two can predict best the behavior at the from stage. We start
with the estimated parameters from the of stage. GP and CK both predict a choice from
the menu, which depends upon the parameters in the of stage. We used, for both
models, and for each subject the estimated parameters from the of stage to predict
behaviour on the choice from the menu (using the two models’ model’s implied
behaviour functionals and corresponding choices. This gives us a prediction log-
12 As mentioned earlier, we have difficulty in estimating the from stage of AS and Stovall since we do not have enough data.
36
likelihood for each functional and for each subject — this is, of course, a measure of
the predictive ability of the theory. We add noise into the choice in the from stage
once again using the Luce method, since GP’s and CK’s modelling of the from stage are
deterministic. Since the decision context is different, we assume that the noise
parameters at the choice from the menu stage are different from those at the choice
of the menu stage.
Table 16 Mean log-likelihood of choice from menu (standard deviation in
parentheses)
GP CK
fitted likelihood -59.37 -23.52
(8.96) (3.45)
According to table 16, CK emerges as the best in this prediction contest13. To check
the significance, we use the Vuong test, as before. The results are in Table 17. This
shows that CK fits significantly better than GP.
13 We also examined the results subject-by-subject; all subjects have a higher prediction log-likelihood with CK than with GP.
37
Table 17 significance tests of comparative model fit
H0: Model 1 and model 2 are equally close to the true model
H1: Model 1 is closer to the true model than model 2
model 1/model 2 GP CK
GP - -8.512
CK 8.512 -
- No meaning
If V> 1.96, model 1 is significantly better than model 2;
If V< -1.96 model 2 is significantly better than model 1;
If |V| < 1.96 model 1 and model 2 are equally close to true model.
7. Conclusions
We report on an experimental investigation into the relative explanatory and
predictive power of four prominent theoretical models of two-stage decision-making.
These models are ones in which the decision maker (DM) makes a choice of a menu in
the first stage and then makes a choice from the chosen menu in the second stage.
The models considered are those of GP (Gul and Pesendorfer, 2001), Stovall (2010), CK
(Chatterjee and Krishna, 2009) and AS (Ahn and Sarver, 2013).
The experiment and particularly the menus were carefully designed so that temptation,
the cost of self-control, possible multiple temptation and flexibility were all
incorporated. In estimation, we use the Luce stochastic specification to incorporate
experimental noise, and hence render the models distinguishable14 (identifiable).
14 AS is distinguishable because of its differences.
38
Our parametric estimation results show that CK generally explains better than the
other models, and also predicts better the choice from the menu than GP. GP and AS
are ranked second on the choice of the menu (with their explanatory powers not
significantly different) while Stovall performs worst.
In our experiment, we use lotteries as the final objects of choice, and define
preferences in terms of the attitude towards risk of the subjects. We follow the
literature in identifying ex ante preferences as those applying to the preferences at the
start of the decision process, and ex post preferences as those applying when the final
decision from the chosen menu is made. Conflicts arise when ex post preferences
depart from ex ante preferences. This raises questions of dynamic consistency, and
hence questions as whether the DM anticipates that there may be this departure.
CK models a particularly simple decision-maker who acts as if her final choice will be
probabilistically made either on the basis of her ex ante preferences or on the basis of
her ex post preferences; in the latter case, the DM, in the language of the literature,
“succumbs” to the temptation of her ex post preferences; the DM anticipates her
behaviour in the choice of the menu. In contrast, GP posits a more sophisticated DM
who anticipates a struggle at the second stage, and takes into account the cost of this
struggle when deciding at the first stage. In stark contrast to this story, AS posits a DM
who totally ignores her ex ante preferences, and bases her decision at the first stage
solely on the basis of her possible ex post preferences. Whereas, in Stovall the DM
anticipates her possible second-stage decisions (which will be based on her ex post
preferences) and evaluates them according to her ex ante preferences.
In our experimental context, we define the final objects of choice as lotteries with
differing degrees of risk. Thus, particular choices are not necessary strictly better or
39
worse than others; this depends on the DM’s attitude to risk. This is in contrast to the
few self-control and temptation experiments, where the temptation and choice
contexts are usually specified and clearly defined as bad or good ̶ such as a willingness
to read gossip (Toussaert, 2018), and using the internet when doing tedious work
(Houser et al, 2010); In these contexts, the motivation of self-control may not be strong
and clear enough. We mainly focus on preference consistency. Thus, rather than in the
deterministic self-control of GP, in the random indulgence model of CK the DM
perceives a positive probability to succumb to the temptation, where there are (ex-
ante) costs from succumbing. It seems that the uncertainty in CK’s model accounts for
behaviour in our experiment. Compared to the uncertainty of CK, Stovall incorporates
uncertainty driven by multiple temptations. Thus, all possible temptations, and not
just the most tempting option, will be taken into consideration. However, we do not
know if subjects are tempted by multiple temptations in our experiment. We can only
infer that the existence of extremely risky or safe options tend to tempt the DM, but
do not know if the subjects are tempted by one of them or by both. Stovall does not
work well compared with the other models, perhaps due to our design.
In the light of our estimation results, we can answer our three main questions
proposed earlier.
First, whether the strength of ex-ante preference or preference flexibility is prevalent
in reality? In our experiment, subjects tended to keep ex-ante preferences and remain
consistent as long as they were not tempted to reverse their preference. As discussed,
only AS addresses a preference for flexibility, where ex-ante preference does not
impinge on subsequent decisions. According to Table 14, the vast majority of subjects’
decisions are best explained by CK, with a small minority explained by GP, in which the
ex-ante preference plays a crucial role. Our results offer insight into choice-overload
40
and preference-consistency research: if the more flexible choice set conflicts with long
term normative preference, having more choices is not necessarily better. As
mentioned earlier, AS and Stovall consider all possibilities of future preferences due to
uncertainty while CK and GP only identify the most tempting one. We can conclude
from our results that only the most attractive option influences decision making in our
context.
Second, as to whether adding middle level problems influences the utility of a menu,
we cannot draw a conclusion, since we cannot know if our designed multiple
temptations do tempt the subjects simultaneously. Our results raise the following
question for future research: when there are multiple diverse options, can subjects be
tempted by multiple extremely conflicting options at the same time?
Third, for GP and CK we can conclude that CK better predicts the choice from the menu;
but our data is insufficient for a conclusion with respect to AS and Stovall.
Overall, our results come down firmly in concluding that CK is the better model of the
four. This could result because of the simplicity of CK: the DM probabilistically either
sticks with her ex-ante preferences or switches to her ex post preferences. It is a simple
story, almost a heuristic, though it is justified by an axiomatic derivation. If one could
test axioms directly, it would be interesting to discover which axiom is the crucial one.
41
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