7: Measurement issues in clinical and health psychological research

Question 1

Conceptualization

Answer 1

Process of specifying what we mean by a term

Question 2

Operationalization

Answer 2

Process of connecting concepts to observations

Question 3

Univariate operational definition

Answer 3

One single test

Question 4

Multivariate definition

Answer 4

Two or more indicators are used

Question 5

Operational definition

Answer 5

what it measures, how the indicators are measured and the rules used to assign value to what is observed.

Question 6

If you need to develop a new scale

Answer 6

Phase 1: initial pool of items; literature review, interviews, focus groups, content validity, cognitive tests

Phase 2: refine the item pool, using exploratory MIRT

Phase 3: psychometric properties, confirmatory MIRT, internal consistency, reliability and discriminant validity.

Question 7

Practical considerations in selecting psychological instruments

Answer 7

• The cost of a test
• Permission and responsibility for using instrument
• Time and length

Question 8

Reliability

Answer 8

• Prerequisite of validity. A valid test is a reliable test, but a reliable test is not always a valid test.
• Infers low error
• A reliable measure is optimally free from random error, while a valid measure is optimally free from random error.

Question 9

Cronbachs alpha

Answer 9

Its a measure for internal consistency.

Its an estimate of the correlation between observed scores and true scores.

Question 10

Assumptions of Cronbach´s alpha

Answer 10

1. the scale adheres to tau equivalent (a statistically way to state that each item on a scale contributes to the total scale score)
2. Scale items are on a continuous scale and normally distributed
3. The error of the items do not covary
4. The scale is unidimensional

Question 11

Item response theory

Answer 11

Refers to a set of mathematical models that describe the relationship between. persons response to a survey question/test item and his or her level of the latent variable being measured by the scale.

This latent variable is usually a hypothetical construct which is postulated to exist but cannot be measured by a single observable variable. instead it is indirectly measured by using multiple items or questions in a multi-item test/scale.

Question 12

What IRT does

Answer 12

IRT models provide a clear statement (picture) of the performance of each item in the scale/test

Question 13

Validity

Answer 13

A measure is valid if it does what it claims to do.

Question 14

Face validity

Answer 14

Refers to the extent to which a measures “appears” to measure what it is supposed to measure.

• not statistical; involves the judgment of the researcher.
• A measure has face validity “if people think it does”.

Question 15

Concurrent validity

Answer 15

Measure and criterion are assessed at the same time

Question 16

Predicitve validity

Answer 16

Elapsed time between the administration of the measure to be validated and the criterion is relatively long period (e.g. months or years). It refers to a measures ability to distinguish participants on a relevant behavioral criterion at some point in the future.

Question 17

Construct validity

Answer 17

Refers to the question of whether a test measures what (an unobservable construct) it purports to measure.

Question 18

Convergent validity

Answer 18

the alternative measure of the same construct should be highly intercorrelated

Question 19

Discriminant validity

Answer 19

The measures of different constructs should be, at most, moderately intercorrelated. it should not correlate with measures that it should not correlated with.

Question 20

Sensitivity

Answer 20

the sensitivity of a test in the ability of the test to identify correctly affected individuals.

Question 21

Specificity

Answer 21

The specificity of a test in the ability of the test to identify correctly non-affected individuals.

Question 22

ROC curve

Answer 22

Its a graphical representation of the trade off between the false negative and false positive rates for every possible cut off.