Validity and Reliability in Instrumentation

47.469: Research I: Basics

Dr. Leonard

February 24, 2010

Recap Research design can be…

experimental or non-experimental (maybe quasi-experimental) basic or applied research laboratory or field setting quantitative or qualitative data collection

Research must be based in solid theory and testable hypotheses

Research must include clear conceptual and operational definitions

Quasi-experimental Occurring more commonly in psychology

Apply experimental principles like cause and effect or group comparison to field, or less controlled settings More like correlational research

Less control over extraneous variables but can take place outside of lab, which may decrease the artificial feeling

Interpretation of results not as clean as in experimental research but closer to “real world” application

Scientific method

1. Formulate theories √√

2. Develop testable hypotheses (operational definitions) √√

3. Conduct research, gather data √√

4. Evaluate hypotheses based on data

5. Cautiously draw conclusions

Next steps…gather data Once you have explicitly clear conceptual and

operational definitions to guide the research, you must develop your measures for collecting data Operational definition proposes type of measures

Instrumentation is the process of selecting or creating measures for a study (the measure is your instrument)

Two overarching goals for instrumentation Validity: the extent to which a measure (operationally

defined) taps the concept it’s designed to measure and not some other concept

Reliability: the consistency or stability of a measure, i.e., same results obtained if measure used again

Caveats

Can never be certain of the validity (or reliability) of our instruments so we try to speculate the degree of validity We might claim “modest” or “partial” validity Hard to capture true essence of a concept/construct and

some concepts/constructs are more elusive than others! An estimate of the validity of our measures depends on the

purpose of the study Keep focused on the hypotheses and operational definitions!

Two types of validity we estimate Judgmental validity Empirical validity

Types of validity: Judgmental Content validity: whether the concept being

measured is a real concept AND whether the measurement being used is the most appropriate one to be using

Is our operationally defined variable (concrete) really capturing the hypothetical concept (abstract) we are interested in studying?

Are we capturing the central meaning?

Concept

Variable/Measure

Types of validity: Judgmental Content validity, or any other type of validity alone, is

never enough to determine if our measure is valid so we consider other types…

Face validity: measure is valid because it makes sense; on the surface, it seems to tap into construct of interest

Face Validity is neither sufficient nor absolutely necessary for overall validity, but is a helpful clue

Could have high face validity but low content validity!

Good face validity?Rosenberg Self-Esteem Scale

1= Strongly Disagree, 7 = Strongly Agree

_____1. I feel that I am a person of worth, at least on an equal basis with others.

_____2. I feel that I have a number of good qualities. _____3. All in all, I am inclined to think that I am a failure.*_____4. I am able to do things as well as most people. _____5. I feel that I do not have much to be proud of.* _____6. I take a positive attitude towards myself. _____7. On the whole, I am satisfied with myself. _____8. I wish I could have more respect for myself.* _____9. I certainly feel useless at times.*_____10. At times I think I am no good at all.*

*Reverse scored

Types of validity: Empirical• Criterion-related Validity: extent to which your

measure of a concept relates to a theoretically meaningful criterion for that concept, a “gold standard” for that concept

• Predictive validity: The measure should be able to predict future behavior that is related to the concept

• E.g., Job skills test and future ratings of performance• Concurrent (convergent) validity: The measure

should be meaningfully related or correlated to some other measure of the behavior

• E.g., Scores on two different job skills tests• Predicitve or concurent validity coefficient: a

number (0-1) based on correlation that quantifies whether the measure is in fact related to other measures it should be related to

Predictive Validity

Job skills test

QualificationFor job

Job skills test

Future performance

ratings

Correlation coefficient = .60

Concurrent (convergent) Validity

Job skills test A

Qualification for job

Job skillsTest A

Job skillsTest B

Job skills test B

Types of validity: Judgmental-Empirical Construct validity represents a combined

approach for estimating validity using 1) a subjective prediction about what other concepts

(indicators) the concept being measured should relate to and.. May relate positively OR negatively

2) an empirical test of whether the concept is in fact related to those other indicators E.g., Depression should be linked to disengagement

from schoolwork among college students so test relationship between depression scores and GPA among a sample of students

Construct Validity exercise Take heart rate for 30 seconds and multiply by 2,

record on separate paper Repeat Average two heart rate measurements Turn in paper Complete Manifest Anxiety Scale Score Turn in sheet Why is this as a test of construct validity?

Reliability

The consistency or stability of a measure; easier to establish when measure is unidimensional

Related to validity? Yes!

Generally, more valid measures tend to be more reliable BUT you could have a highly reliable measure that is low in validity Think of gun shooting a target example

Like validity, reliability can be estimated by a correlation coefficient (0-1) Generally, to be respectable in the scientific community, reliability

should be .80 (80%) or higher

Relationship between reliability and validity

Is our measure RELIABLE? Does it have consistency and stability in measurement?

Is our measure VALID? Does it measure what it’s supposed to measure?

Validity is more important to a research study; reliability can’t tell us if we are measuring the correct concept, only if we are measuring something consistently.

Classical Test Theory

An observed measurement (or score, X) is comprised of a true score (T, the score that would be obtained if there was no measurement error) and some random measurement error (E).

X = T + E

X is the observed scoreT is the true scoreE is the measurement error

Types of Reliability Test-retest reliability - consistent results from same

measure under same conditions two times Across time

Inter-rater reliability - consistent results when same measure is given twice, but with different test givers, or have two independent observers code some behavior Across raters or observers

Alpha reliability - individual items/questions from a scale measuring same concept are correlated Across items

Split-half reliability - items from one part of a scale are correlated and measure same concept as another part Across items

Test-retest reliability (across time)

ID

Time 1

X

Time 2

X

1

2

3

4

18

12

29

25

19

13

28

25

Inter-rater reliability (across raters)

ID

Rater 1

X

Rater 2

X

Rater 3

X

1

2

3

4

18

12

29

25

19

13

28

25

20

14

27

24

Alpha reliability (across items)

ID

Item 1

X1

Item 2

X2

(Reversed)

Item 3

X3

Item 4

X4

(Reversed)

Item 5

X5

(Reversed)

Item 6

X6

1

2

3

4

4

3

2

1

4

2

1

1

5

4

3

2

4

3

1

1

4

3

2

1

5

4

4

2

Sometimes called internal consistency

Split-half reliability (across items)

ID

First 1/2 items

Second 1/2 items

1

2

3

4

5

6

7

8

9

10

1

2

3

3

2

3

1

2

2

1

1

2

2

3

1

2

1

2

2

2

Sometimes called internal consistency

The more, the better

As with validity, it is always better if you can estimate or test for multiple forms of reliability! Sometimes called parallel-forms reliability if

measure is available in more than one version and can be given in both ways and then compared

Valid? Reliable? Concept: Parental engagement in child’s academic

development

How often do you help your child with his/her homework (please check one)?

_Never_Rarely_Sometimes_Often_Everyday

Concept? Valid? Reliable?

Is there a chance that you could get HIV/AIDS?

1--------------------2--------------------3 Not at Small chance Yes

All Definitely

Do you worry about getting HIV/AIDS? (circle one number)

1--------------------2--------------------3--------------------4--------------------5 Never Almost Sometimes Often

Very Never Often

Concept? Valid? Reliable?

How important is financial success to you? _Very important _Somewhat important _Not at all important

How important is it for you to have nice things?_Very important _Somewhat important _Not at all important

Our total MAS scores and average heart rate were only correlated at -.04; correlational relationships can have a magnitude from 0-1 but also a direction (+ or -)

Correlation between Heart Rate and MAS Score

Linear Regression

10 20 30

MAS_total

30.00

35.00

40.00

45.00

Heart_rate

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

A

Heart_rate = 40.04 + -0.02 * MAS_total

R-Square = 0.00

Good construct validity? Why?

Good predictive validity? Why?

Beginning APA style for your proposal

Author last name, author first and middle initials. (Year published). Title of article. Title of Journal, Volume number (Issue number), pg.-pg.

Morelli, G. A., Rogoff, B., Oppenheim, D., & Goldsmith, D. (1996). Cultural variations in infants’ sleeping arrangements: Questions of independence. Developmental Psychology, 28(4), 604-613.

Put the following three articles into an APA style reference

Three APA references

Samuolis, J., Layburn, K., & Schiaffino, K. M. (2001). Identity development and attachment to parents in college students. Journal of Youth and Adolescence, 30 (3), 373-383.

Tripodi, S. J., Bender, K., Litschge, C., & Vaughn, M. G. (2010). Interventions for reducing adolescent alcohol abuse: A meta-analytic review. Archives of Pediatric and Adolescent Medicine, 164 (1), 85-91.