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Measurement ErrorWhatever measurement we might make with

regard to some psychological construct, we do so with some amount of errorAny observed score for an individual is their true score

with error added in

There are different types of “error”, but here we are concerned with a measure’s inability to capture the true response for an individualObserved Score = True score + Error of measurement

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ReliabilityReliability refers to a measure’s ability to capture an

individual’s true score, i.e. to distinguish accurately one person from another

While a reliable measure will be consistent, consistency can actually be seen as a by-product of reliability, and in a case where we had perfect consistency (everyone scores the same and gets the same score repeatedly), reliability coefficients could not be calculated No variance/covariance to give a correlation

The error in our analyses is due to individual differences but also the lack of the measure being perfectly reliable

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Reliability Criteria of reliability

Test-retest Test components (internal consistency)

Test-retest reliability Consistency of measurement for individuals over time

The score similarly e.g. today and 6 months from now Issues

Memory If too close in time the correlation between scores is due to memory of item

responses rather than true score captured Chance covariation

Any two variables will always have a non-zero correlation Reliability is not constant across subsets of a population

General IQ scores good reliability IQ scores for college students, less reliable

Restriction of range, fewer individual differences

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Internal ConsistencyWe can get a sort of average correlation

among items to assess the reliability of some measure1

As one would most likely intuitively assume, having more measures of something is better than few

It is the case that having more items which correlate with one another will increase the test’s reliabilityvideo.edhole.com

What’s good reliability?While we have conventions, it really kind of dependsAs mentioned reliability of a measure may be different

for different groups of peopleWhat we may need to do is compare reliability to those

measures which are in place and deemed ‘good’ as well as get interval estimates to provide an assessment of the uncertainty in our reliability estimate

Note also that reliability estimates are biased upwardly and so are a bit optimistic

Also, many of our techniques do not take into account the reliability of our measures, and poor reliability can result in lower statistical power i.e. an increase in type II errorThough technically increasing reliability can potentially also

lower power1

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Replication and Reliability While reliability implies replicability, assessing reliability does not

provide a probability of replication Note also that statistical significance is not a measure of reliability or

replicability1

Replication is not perhaps conducted as much as should be in psychology for a number of reasons Practical concerns, lack of publishing outlets etc.

Furthermore, knowing our estimates are biased and variable themselves, we might even think that in many cases we would not expect consistent research findings

In psychology, many people spend a lot of time debating back and forth about the merits of some theory, citing cases where it did or did not replicate

However the lack of replication could be due to low power, low reliability, problem data, incorrectly carrying out the experiment etc. In other words, we didn’t repeat because of methodology, not because

the theory was wrong

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Factors affecting the utility of replicationsYou can’t step in the same river twice!

Heraclitus1

WhenLater replications are not providing as much

information, however they can contribute greatly to the overall assessment of an effect Meta-analysis

HowThere is no perfect replication (different people

involved, time it takes to conduct etc.)Doing ‘exact’ replication gives us more confidence in the

original finding (should it hold), but may not offer much in the way of generalization Example: doing a gender difference study at UNT over and

over. Does it work for non-college folk? People outside of Texas?

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Factors affecting the utility of replicationsBy whom

It is well known that those with a vested interest in some idea tend to find confirming evidence more than those that don’t

Replications by others are still being done by those with an interest in that research topic and so may have a ‘precorrelation’ inherent in their attempt Direct: correlation of attributes of persons involved Indirect: correlation of data to be obtained

Gist, we can’t have truly independent replication attempts, but must strive to minimize bias

The more independent replication attempts are, the more informative they will bevideo.edhole.com

ValidityValidity refers to the question of whether our

measurements are actually hitting on the construct we think they are

While we can obtain specific statistics for reliability (even different types), validity is more of a global assessment based on the evidence available

We can have reliable measurements that are invalidClassic example: The scale which is consistent and able

to distinguish from one person to the next but actually off by 5 pounds

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Validity Criteria in Psychological Testing Content validity Criterion validity

Concurrent Predictive

Construct-related validity Convergent Discriminant

Content validity Items represent the kinds of material (or content areas) they are

supposed to represent Are the questions worth a flip in the sense they cover all domains of a

given construct? E.g. job satisfaction = salary, relationship w/ boss, relationship w/ coworkers

etc.video.edhole.com

Validity Criteria in Psychological TestingCriterion validity

the degree to which the measure correlates with various outcomes Does some new personality measure correlate with the Big 5

ConcurrentCriterion is in the present

Measure of ADHD and current scholastic behavioral problems

PredictiveCriterion in the future

SAT and college gpavideo.edhole.com

Validity Criteria in Psychological TestingConstruct-related validity

How much is it an actual measure of the construct of interest

ConvergentCorrelates well with other measures of the construct

Depression scale correlates well with other dep scales

DiscriminantIs distinguished from related but distinct constructs

Dep scale != Stress scale

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Validity Criteria in Experimentation Statistical conclusion validity

Is there a causal relationship between X and Y? Correlation is our starting point (i.e. correlation isn’t causation, but

does lead to it) Related to this is the question of whether the study was sufficiently

sensitive to pick up on the correlation Internal validity

Has the study been conducted so as to rule out other effects which were controllable? Poor instruments, experimenter bias

External validity Will the relationship be seen in other settings?

Construct validity Same concerns as before

Ex. Is reaction time an appropriate measure of learning?video.edhole.com

SummaryReliability and Validity are key concerns in

psychological researchPart of the problem in psychology is the lack of

reliable measures of the things we are interested in1

Assuming that they are valid to begin with, we must always press for more reliable measures if we are to progress scientificallyThis means letting go of supposed ‘standards’ when they

are no longer as useful and look for ways to improve current onesvideo.edhole.com