Uncertainty about Government Policy
and Stock Prices
Lubos Pastor
and
Pietro Veronesi
Booth School of Business
University of Chicago
NBER, CEPR
May 2010
What We Do
• We analyze how changes in government policy affect stock prices
What We Do
• We analyze how changes in government policy affect stock prices
• We develop a general equilibrium model featuring
– Government with economic and political motives
What We Do
• We analyze how changes in government policy affect stock prices
• We develop a general equilibrium model featuring
– Government with economic and political motives
– Uncertainty about government policy
1. Policy uncertainty
2. Political uncertainty
What We Find
• Government changes its policy after downturns in profitability
What We Find
• Government changes its policy after downturns in profitability
• Policy changes increase volatility, risk premia, correlations
What We Find
• Government changes its policy after downturns in profitability
• Policy changes increase volatility, risk premia, correlations
• Stock prices fall at announcements of policy changes, on average
What We Find
• Government changes its policy after downturns in profitability
• Policy changes increase volatility, risk premia, correlations
• Stock prices fall at announcements of policy changes, on average
– Prices rise if the old policy was sufficiently unproductive,but they fall on average (in expectation)
What We Find
• Government changes its policy after downturns in profitability
• Policy changes increase volatility, risk premia, correlations
• Stock prices fall at announcements of policy changes, on average
– Prices rise if the old policy was sufficiently unproductive,but they fall on average (in expectation)
– Expected stock price drop at the announcement is large
∗ when policy/political uncertainty is large
∗ when policy change is induced by a short or shallow downturn
– Distribution of announcement returns is left-skewed
What We Find
• Government changes its policy after downturns in profitability
• Policy changes increase volatility, risk premia, correlations
• Stock prices fall at announcements of policy changes, on average
– Prices rise if the old policy was sufficiently unproductive,but they fall on average (in expectation)
– Expected stock price drop at the announcement is large
∗ when policy/political uncertainty is large
∗ when policy change is induced by a short or shallow downturn
– Distribution of announcement returns is left-skewed
• Prices rise at announcements of policy decisions, on average
What We Find (cont’d)
• Government’s ability to change policy
– can imply a higher or lower level of stock prices
– amplifies stock price declines around policy changes
What We Find (cont’d)
• Government’s ability to change policy
– can imply a higher or lower level of stock prices
– amplifies stock price declines around policy changes
• Uncertainty about government policy reduces investment
Model
• Finite horizon [0, T ], continuum of equity-financed firms i ∈ [0, 1]
• Firm i’s profitability:
dΠit = (µ + gt) dt + σdZt + σ1dZi,t
gt = impact of government policy on average profitability
Model
• Finite horizon [0, T ], continuum of equity-financed firms i ∈ [0, 1]
• Firm i’s profitability:
dΠit = (µ + gt) dt + σdZt + σ1dZi,t
gt = impact of government policy on average profitability
• Government can change policy at a given time τ , 0 < τ < T
⇒ gt is a step function:
∗ Policy change ⇒ gt changes from gold to gnew
∗ No policy change ⇒ gt stays at gold
Policy Uncertainty
• Key assumption: gt is unknown to all agents
Policy Uncertainty
• Key assumption: gt is unknown to all agents
• Prior distribution is the same for both old and new policies:
gold ∼ N0, σ2
g
gnew ∼ N0, σ2
g
• Define σg ≡ policy uncertainty
– Uncertainty about government policy’s impact on profitability
Objective Functions
• Firms are owned by investors who maximize expected utility:
u (WT ) =W
1−γT
1 − γ
where γ > 1 and WT denotes total capital of all firms at time T
Objective Functions
• Firms are owned by investors who maximize expected utility:
u (WT ) =W
1−γT
1 − γ
where γ > 1 and WT denotes total capital of all firms at time T
• Government is “quasi-benevolent”: it solves
max
Eτ
W1−γT
1 − γ|no policy change
, Eτ
CW1−γT
1 − γ|policy change
C = political cost incurred by government if policy is changed
(C > 1 ⇒ cost; C < 1 ⇒ benefit)
Political Uncertainty
• Government knows C but investors don’t
Political Uncertainty
• Government knows C but investors don’t
• Investors perceive C as random, lognormal with mean E[C] = 1:
c = log (C) ∼ N
−
1
2σ2c , σ2
c
• Define σc ≡ political uncertainty
– Uncertainty about whether government policy will change
– Introduces an element of surprise into policy changes
Learning
• Government & investors learn about gt in a Bayesian fashionby observing profitability of each firm
Learning
• Government & investors learn about gt in a Bayesian fashionby observing profitability of each firm
• Proposition 1: The posterior beliefs are
gt ∼ Ngt, σ
2t
where ∀t ≤ τ ,
dgt = σ2tσ
−1dZt; σ2
t =1
1σ2
g
+ 1σ2t
• A policy change resets beliefs about gt from the posteriorN
(
gτ , σ2τ
)
to the prior N(
0, σ2g
)
; learning continues after time τ
Optimal Changes in Government Policy
• Government changes its policy at time τ iff
Eτ
CW1−γT
1 − γ| policy change
> Eτ
W1−γT
1 − γ| no policy change
Optimal Changes in Government Policy
• Government changes its policy at time τ iff
Eτ
CW1−γT
1 − γ| policy change
> Eτ
W1−γT
1 − γ| no policy change
• Proposition 2: A policy change occurs iff
gτ < g(c)
where
g(c) = −
(
σ2g − σ2
τ
)
(γ − 1) (T − τ )
2−
c
(T − τ ) (γ − 1)
• Investors don’t know c ⇒ cannot fully anticipate a policy change
Policy Changes Tend to Occur After Downturns
• Threshold g(c) is typically negative
• For the posterior mean to be negative while the prior mean is zero,realized profitability must be unexpectedly low
⇒ Policy changes tend to occur after “downturns”
Policy Changes Tend to Occur After Downturns
• Threshold g(c) is typically negative
• For the posterior mean to be negative while the prior mean is zero,realized profitability must be unexpectedly low
⇒ Policy changes tend to occur after “downturns”
• Example: Average across many paths simulated from our model
Table 1: Parameter Choices
σg σc µ σ σi T τ γ
0.02 0.10 0.10 0.05 0.10 20 10 5
0 2 4 6 8 10 12 14 16 18 20−3
−2
−1
0
1
2
3
Time
Pro
fita
bility (
%)
Panel A. Policy Change
Realized Profitability
Expected Profitability
Threshold
0 2 4 6 8 10 12 14 16 18 20−3
−2
−1
0
1
2
3
Time
Pro
fita
bility (
%)
Panel B. No Policy Change
Realized Profitability
Expected Profitability
Threshold
Figure 1. Profitability dynamics and the policy decision.
0 5 10 15 20−5
−4
−3
−2
−1
0
1
Time
Pro
fita
bili
ty (
%)
Panel A. σ c = 0, σ
g = 1%
Realized Profitability
Expected Profitability
Threshold
0 5 10 15 20−5
−4
−3
−2
−1
0
1
Time
Pro
fita
bili
ty (
%)
Panel B. σ c = 20%, σ
g = 1%
Realized Profitability
Expected Profitability
Threshold
0 5 10 15 20−5
−4
−3
−2
−1
0
1
Time
Pro
fita
bili
ty (
%)
Panel C. σ c = 0, σ
g = 3%
0 5 10 15 20−5
−4
−3
−2
−1
0
1
Time
Pro
fita
bili
ty (
%)
Panel D. σ c = 20%, σ
g = 3%
Figure 2. Profitability dynamics conditional on a policy change:
The roles of policy uncertainty and political uncertainty.
Stock Prices
• Firm i’s stock is a claim on the firm’s liquidating dividend BiT
• Market value of stock i is given by
M it = Et
πT
πtBi
T
• Complete markets ⇒ State price density is uniquely given by
πt =1
λEt
W
−γT
,
where total wealth WT is the sum of all BiT ’s
• Risk-free rate = 0
Stock Price Reaction to the Announcement of a Policy Change
• Proposition 3: Closed-form solution for stock return atthe announcement of a policy change, R(gτ )
Stock Price Reaction to the Announcement of a Policy Change
• Proposition 3: Closed-form solution for stock return atthe announcement of a policy change, R(gτ )
• Proposition 4: R(gτ ) < 0 iff gτ > g∗, where
g∗ = −σ2
g − σ2τ
(T − τ )
γ −
1
2
< 0
– Cash flow versus discount rate effects
Stock Price Reaction to the Announcement of a Policy Change
• Proposition 3: Closed-form solution for stock return atthe announcement of a policy change, R(gτ )
• Proposition 4: R(gτ ) < 0 iff gτ > g∗, where
g∗ = −σ2
g − σ2τ
(T − τ )
γ −
1
2
< 0
– Cash flow versus discount rate effects
• P2 + P4 ⇒ Policy change occurs and stock prices fall iff
g∗ < gτ < g(c)
– The interval is expected to be below zero since g∗ < g(0) < 0
0
50
100
150
200
g∗ g(0)gτ 0
Fre
quency d
istr
ibutio
n
Panel A.
0
50
100
150
200
g∗ g(0)gτ 0
Panel B.
0
50
100
150
200
g∗ g(0) gτ 0
Fre
quency d
istr
ibutio
n
Panel C.
0
50
100
150
200
g∗ g(0) gτ0
Panel D.
Figure 3. Probability of a policy change, as perceived by investors just before τ .
Expected Return at the Announcement of a Policy Change
• EAR = Expected return at the announcement of a policy change
• Proposition 5: EAR is negative (E {R(gτ )} < 0)
Expected Return at the Announcement of a Policy Change
• EAR = Expected return at the announcement of a policy change
• Proposition 5: EAR is negative (E {R(gτ )} < 0)
– Positive announcement returns tend to be small becausethey occur when the policy change is anticipated
– Negative announcement returns tend to be large becausethey occur when the policy change comes as a surprise
Expected Return at the Announcement of a Policy Change
• EAR = Expected return at the announcement of a policy change
• Proposition 5: EAR is negative (E {R(gτ )} < 0)
– Positive announcement returns tend to be small becausethey occur when the policy change is anticipated
– Negative announcement returns tend to be large becausethey occur when the policy change comes as a surprise
– Some utility-increasing policy changes reduce stock prices
Expected Return at the Announcement of a Policy Change
• EAR = Expected return at the announcement of a policy change
• Proposition 5: EAR is negative (E {R(gτ )} < 0)
– Positive announcement returns tend to be small becausethey occur when the policy change is anticipated
– Negative announcement returns tend to be large becausethey occur when the policy change comes as a surprise
– Some utility-increasing policy changes reduce stock prices
– Investors expect government to derive a political benefit froma policy change: E(C|policy change) < E(C) = 1
Expected Return at the Announcement of a Policy Change
• EAR = Expected return at the announcement of a policy change
• Proposition 5: EAR is negative (E {R(gτ )} < 0)
– Positive announcement returns tend to be small becausethey occur when the policy change is anticipated
– Negative announcement returns tend to be large becausethey occur when the policy change comes as a surprise
– Some utility-increasing policy changes reduce stock prices
– Investors expect government to derive a political benefit froma policy change: E(C|policy change) < E(C) = 1
• EAR is more negative when policy/political uncertainty is large
0 2 4 6 8 10 12 14 16 18 20−2
−1.8
−1.6
−1.4
−1.2
−1
−0.8
−0.6
−0.4
−0.2
0
σc (%)
Retu
rn (
%)
σg = 1%
σg = 2%
σg = 3%
Figure 4. Expected announcement return.
Determinants of the Announcement Return
• We relate the announcement return to the length and depth
of the downturns that induce policy changes
Determinants of the Announcement Return
• We relate the announcement return to the length and depth
of the downturns that induce policy changes
• Let t0 mark the beginning of a downturn: gt0 = 0
LENGTH = τ − t0
DEPTH =gτ
Std(gτ ). . . number of std dev’s by which gt drops
• Note that
gτ |gt0 = 0 ∼ N (0, Std(gτ )) , where Std(gτ ) =√√√√σ2
t0− σ2
τ
−2.5 −2 −1.5 −1 −0.5 0 0.5−20
−15
−10
−5
0
Depth
Re
turn
(%
)
Panel A. Announcement Return
−2.5 −2 −1.5 −1 −0.5 0 0.50
0.2
0.4
0.6
0.8
1
Depth
Pro
ba
bili
ty
Panel B. Probability of a Policy Change
Length = 10
Length = 5
Length = 1
Length = 10
Length = 5
Length = 1
Figure 5. Announcement return and the downturn length and depth.
−2 −1 0 1 2−15
−10
−5
0
Depth
Retu
rn (
%)
Panel A. Announcement Return, σg = 1%
−2 −1 0 1 20
0.2
0.4
0.6
0.8
1
Depth
Pro
babili
ty
Panel C. Probability of a Policy Change, σg = 1%
−5 −4 −3 −2 −1 0−30
−25
−20
−15
−10
−5
0
Depth
Retu
rn (
%)
Panel B. Announcement Return, σg = 3%
−5 −4 −3 −2 −1 00
0.2
0.4
0.6
0.8
1
Depth
Pro
babili
ty
Panel D. Probability of a Policy Change, σg = 3%
Length = 10
Length = 5
Length = 1
Figure 6. Announcement return and the downturn length and depth:
The role of policy uncertainty.
0 2 4 6 8 10 12 14 16 18 20−6
−5
−4
−3
−2
−1
0
σc (%)
Re
turn
(%
)
Panel A. Expected Announcement Return. Length = 5 years
σg = 1%
σg = 2%
σg = 3%
0 2 4 6 8 10 12 14 16 18 20−20
−15
−10
−5
0
σc (%)
Re
turn
(%
)
Panel B. Expected Announcement Return. Length = 1 years
σg = 1%
σg = 2%
σg = 3%
Figure 7. Expected announcement return and the downturn length.
−20 −15 −10 −5 00
10
20
30
40
50
Return (%)
Fre
qu
en
cy D
istr
ibu
tion
Panel A. σc = 10%
−20 −15 −10 −5 00
10
20
30
40
Return (%)
Fre
qu
en
cy D
istr
ibu
tion
Panel B. σc = 20%
σg = 1 %
σg = 2 %
σg = 3 %
σg = 1 %
σg = 2 %
σg = 3 %
Figure 8. Probability distribution of stock returns on the day of the announcement
of a policy change.
Expected Return at the Announcement of a Policy Decision
• Expected jump in stock prices at time τ is generally positive
Expected Return at the Announcement of a Policy Decision
• Expected jump in stock prices at time τ is generally positive
– It is negative iff g∗ < gτ < g∗∗, where
g∗∗ = −γ
2(T − τ )
σ2
g − σ2τ
< 0
• Investors demand a premium for facing jumps in SDF
E(
JM,τ
)
= −Cov(
Jπ,τ , JM,τ
)
0 2 4 6 8 10 12 14 16 18 200
0.1
0.2
0.3
0.4
σc (%)
Re
turn
(%
)
Panel A. Expected Return at Announcement of a Policy Decision
0 2 4 6 8 10 12 14 16 18 20−5
−4
−3
−2
−1
0
σc (%)
Re
turn
(%
)
Panel B. Expected Return at Announcement of Policy Change
σg = 1%
σg = 2%
σg = 3%
0 2 4 6 8 10 12 14 16 18 200
1
2
3
4
5
σc (%)
Re
turn
(%
)
Panel C. Expected Return at Announcement of No Policy Change
σg = 1%
σg = 2%
σg = 3%
σg = 1%
σg = 2%
σg = 3%
Figure 9. Expected return at the announcement of a policy decision.
Dynamics of Stock Returns
• We derive closed-form solutions for the dynamics of
– the stochastic discount factor
– expected return of each stock
– volatility of stock returns
– correlations between stocks
9 9.5 10 10.5 1110
15
20
25
30
Time
Pe
rce
nt
pe
r ye
ar
Panel C. Return Volatility
σg=1%
σg=2%
σg=3%
9 9.5 10 10.5 1120
40
60
80
100
Time
Pe
rce
nt
Panel D. Correlation
σg=1%
σg=2%
σg=3%
9 9.5 10 10.5 1120
40
60
80
100
120
Time
Pe
rce
nt
pe
r ye
ar
Panel A. SDF Volatility
σg=1%
σg=2%
σg=3%
9 9.5 10 10.5 110
5
10
15
20
25
30
Time
Pe
rce
nt
pe
r ye
ar
Panel B. Expected Return
σg=1%
σg=2%
σg=3%
Figure 10. Properties of returns around policy changes.
Price Dynamics When Policy Changes Are Precluded
• We compare model-implied stock prices with their counterpartsin the hypothetical scenario in which policy changes are precluded
• We find that the government’s ability to change policy
– can increase or decrease market values
– amplifies stock price declines around policy changes
9 9.5 10 10.5 112
2.1
2.2
2.3
2.4
2.5Panel A. Market Value, Length = 1
Time
Policy change allowed
Policy change precluded
9 9.5 10 10.5 1112
13
14
15
16
17
18Panel C. Volatility, Length = 1
Time
Pe
rce
nt
pe
r ye
ar
9 9.5 10 10.5 112.25
2.3
2.35
2.4
2.45
2.5Panel B. Market Value, Length = 5
Time
9 9.5 10 10.5 1110
12
14
16
18Panel D. Volatility, Length = 5
Time
Pe
rce
nt
pe
r ye
ar
Figure 11. The level and volatility of stock prices around policy changes.
Extension: Endogenous Timing of Policy Change
• We extend the model by endogenizing the timing of policy change
– No closed-form solutions; solve numerically
• Government can change policy at any time τ ∈ [1, 2, . . . , 19]
• Each year i, a new value of Ci is drawn; Ci are iid
• Value function reflects option value of waiting
• We find our results continue to hold when τ is endogenous
0 5 10 15 20
−4
−3
−2
−1
0Panel A. Announcement Return
σc (%)
Pe
rce
nt
σg = 1%
σg = 2%
σg = 3%
5 10 15 20−10
−8
−6
−4
−2
0Panel B. Announcement Return
Policy Announcement Date
Pe
rce
nt
σg = 1%
σg = 2%
σg = 3%
−1 −0.5 0 0.5 110
12
14
16
18
20Panel C. Return Volatility
Time Relative to Policy Announcement Date
Pe
rce
nt
pe
r ye
ar
σg = 1%
σg = 2%
σg = 3%
−1 −0.5 0 0.5 120
30
40
50
60
70Panel D. Correlation
Time Relative to Policy Announcement Date
Pe
rce
nt
σg = 1%
σg = 2%
σg = 3%
Figure 12. Endogenous timing of a policy change.
Extension: Investment Adjustment
• We extend the model by allowing firms to disinvest
• At time τ , each firm can disinvest and switch capital into cash
• Firms make investment decisions at the same time as governmentmakes the policy decision
Extension: Investment Adjustment
• We extend the model by allowing firms to disinvest
• At time τ , each firm can disinvest and switch capital into cash
• Firms make investment decisions at the same time as governmentmakes the policy decision
• Proposition 7: In Nash equilibrium, a fraction ατ ∈ [0, 1] offirms continue investing. The government changes its policy iff
gτ < g (c, ατ )
• We solve the problem numerically
– The threshold g (c, ατ ) depends on ατ , which depends on gτ
Extension: Investment Adjustment (cont’d)
• For parameter values in Table 1, the equilibrium has ατ = 1(no disinvestment), so all results continue to hold
– To obtain disinvestment, we reduce µ from 10% to 2%
Extension: Investment Adjustment (cont’d)
• For parameter values in Table 1, the equilibrium has ατ = 1(no disinvestment), so all results continue to hold
– To obtain disinvestment, we reduce µ from 10% to 2%
• We find:
– Both policy and political uncertainty reduce investment
– Our key asset pricing results continue to hold
0 5 10 15 20−1.5
−1
−0.5
0
σc (%)
Retu
rn (
%)
Panel B. Announcement Return
σg = 1%
σg = 2%
σg = 3%
0 5 10 15 2070
75
80
85
90
95
100
σc (%)
α (
%)
Panel A. Equilibrium α
σg = 1%
σg = 2%
σg = 3%
9 9.5 10 10.5 1110
15
20
25
Time
Perc
ent per
year
Panel C. Return Volatility
σg=1%
σg=2%
σg=3%
9 9.5 10 10.5 1120
40
60
80
100
Time
Perc
ent
Panel D. Correlation
σg=1%
σg=2%
σg=3%
Figure 13. Investment adjustment.
Conclusions: Key Empirical Predictions
• Stock returns at announcements of policy changes should benegative, on average
– Especially when policy/political uncertainty is high, or whenpolicy change is induced by a short or shallow downturn
– Distribution of announcement returns should be left-skewed
• Stock returns at announcements of policy decisions should bepositive, on average
• Policy changes should increase volatilities, risk premia, andcorrelations