Personality Test Development

Introduction to Clinical Psychology

Discussion Section #8 and #9

Personality Test Construction

Goal: Gain an increased understanding of the

concepts reliability and validity as they pertain to tests

Gain an increased understanding of test development methods

Test Construction Procedure

1. Identify a need for a new test

2. Assemble an item pool (decide on scale and item formats)

3. Pilot item pool

4. Select “good” items

5. Examine test’s psychometric properties (reliability and validity)

1. Identify Need for a New Test

What is the objective of the new test/is there really a need for it

How will the test be administered? What is the ideal item format for this test? Should more than one form be developed? What special training will be required of test

users in terms of administering or interpreting the test?

2. Assemble Item Pool

Two decisions: Content Format

Content

Develop a pool of items that fully measure the construct

Example: Depression What items should be included in the

pool?

Format

Dichotomous (true false) Polychotomous (multiple choice) Likert scales (degree of agreement) …many others

3. Pilot Item Pool

Try the pool of items out on people for whom the test is being developed

Test should be administered under conditions similar to those that the developed test will be administered (e.g. same instructions, time frame, time limits)

4. Select “Good” Items

Selecting “good” items involves complex statistical analysis of the test results which varies according to the purpose of the test.(called item analysis)

However, in tests of attitudes or personality characteristics one consideration is whether individuals endorse the full range of the scale provided.

5. Examine Test’s Psychometric Properties

Does the test yield consistent results (reliability)?

Do the test items measure the intended construct (validity)?

Test Construction Exercise: Part 1

Develop a test that distinguishes first and later born children

Test Construction Exercise: Procedure

Divide into groups of 4 to 5 studentsIn Class As a group, develop an item to distinguish first

born from later born children Note: use a personality construct and not a

physical characteristic (e.g. I have no older siblings)

Develop two responses for the item Once your item is ready, tell Sara or Eunyoe

so they can write it on the board (so others won’t give the same item)

Administer Test

Item % First Born Agree

% Later Born Agree

Administer Final Test and Score!

Psychometric Properties of Tests

Reliability and Validity

Reliability

Consistency of the observations or measurements

Reliability is inversely related to the degree of error in the instrument.

High measurement error translates to low reliability

Low measurement error translates to high reliability

What !?

What does this mean!?

High measurement error translates to low reliability

Low measurement error

translates to high reliability

Easy Example: A broken scale

There will be high measurement error on a broken scale, correct?

How consistent are the weights likely to be on a broken scale?

Is a broken or working scale going to have more error?

Is the broken or working scale going to be more reliable?

Types of Measurement Error

Random

Factors unpredictably influence measurements.

Examples:

Mood, environmental distractions, hunger or motivation interfere with the responses.

Systematic

A persistent bias in the test or in the interpretations made by examiner.

Systematic errors, because they are consistently made will not affect reliability but they will affect validity

Types of Reliability

Inter-rater reliability (relevant to observational systems and psychological assessments requiring ratings or judgment)

Test-retest reliability Split-half

Note: Each form of reliability is not equally important for every assessment method

Inter-rater Reliability

Degree of correspondence between two raters

Inter-rater reliability of diagnoses based on DSM criteria improved with DSM-III and the development of operational criteria for most of the mental disorders

Note: We will learn how to calculate next week!.

Test-Retest Reliability

The consistency of results over periods of time.

The consistency of the results for a test given at two different time periods

The correlation of test result scores

Quantifying Test-Retest Reliability

Reliability is expressed as a correlation coefficient

Values range from 0 (not at all consistent or reliable) to 1 ( perfectly consistent and reliable.

The value for adequate reliability is about .80 or greater

Factors Affecting Test-Retest Reliability Estimates

Length of the intervening interval Stability of the measured trait

For example: In characteristics that are stable, like intelligence, the

interval of time between the two tests should not affect the stability of the results.

In contrast, in characteristics that are not stable, like depressed mood, the longer the interval between tests, the less reliable or consistent the scores. (not necessarily bad)

Split Half Reliability

The consistency of scores on two halves of the test

Validity

A test can be reliable (consistently give the same results) but not valuable.

Why?

If the test does not measure the correct construct, then it is not useful even if the results are consistent.

Validity

The degree to which a test measures what it is designed or intended to measure.

Types of Validity

Face validity Content validity Criterion validity (predictive and

concurrent) Discriminant Construct validity

Face Validity

A judgment about the relevance of test items A type of validity that is more from the

perspective of the test taker as opposed to the test user

Example: Personality testsIntroversion-Extroversion test will be perceived

as a highly (face) valid measure of personality functioning

The inkblot test may not be perceived as a (face) valid method of personality functioning

Content Validity

Degree to which the measure covers the full range of the (personality) construct.

and Degree to which the measure excludes

factors that are not representative of the construct

Criterion Validity

The degree to which the test results (from your measure) are correlated with another related construct.

WHAT!?

For example: the degree to which scores on an intelligence test are correlated with school performance or achievement.

Types of Criterion Validity Concurrent: the two constructs are assessed at the same

time Predictive: one construct may be measured at a later

date

For example:Concurrent: the correlation of SAT score with G.P.A. at the

time of taking the SAT in high school.Predictive: the correlation of SAT score taken in high school

with final G.P.A. upon graduating from college

Discriminant Validity The degree to which the score on a measure

of a personality trait does not correlate with scores on measures of traits that are unrelated with the trait under investigation.

For example: (from text)Trait being measured: phobiaUnrelated trait: intelligenceYou would not expect the score on your phobia

scale to be correlated with the score on an intelligence test

Construct Validity

The degree to which the measure reflects the structure and features of the hypothetical construct that is being measured

Measured by combining all these aspects of validity.

Exercise: Reliability and Validity applied to the Edinburgh Postnatal Depression Scale (EPDS)

Let’s consider reliability and validity in the context of a real measure: the EPDS

What is the Edinburgh Postnatal Depression Scale (EPDS)?

John Cox, Jenifer Holden & Ruth Sagovsky

10 item depression screening tool (reliable and valid)

Simple to complete Acceptable to

mothers and health workers

What is the Edinburgh Postnatal Depression Scale (EPDS)?

Psychometric Characteristics 10 item scale Assesses mood aspects of depression

not confounding somatic symptoms Acceptable to women Validated Translated into many languages

Stems of all 10 EPDS Items I have been able to laugh and see the funny side

of things. I have looked forward with enjoyment to things. I have blamed myself unnecessarily when things

went wrong. I have been anxious or worried for no good reason. Things have been getting on top of me.

Stems of all 10 EPDS Items (cont)

I have felt scared or panicky for no very good reason.

I have been so unhappy that I have had difficulty sleeping.

I have felt sad or miserable. I have been so unhappy that I have been

crying. The thought of harming myself has occurred to

me.

Psychometric Evaluation of the EPDS: An Exercise

Is the EPDS a good measure of depression?

Psychometrically, what does it mean to ask if the EPDS is a “good” measure of depression?

Note: Follow the questions on the handout

Handout Questions

Test Construction Exercise:Part 2: Evaluating Developed Tests

1. Regroup into your “test groups”

2. Evaluate items in terms of content validity and adequacy of scales

3. Select final items for test

4. Propose methods for evaluating reliability and validity of new measure