Chapter 9

Correlation, Validity and Reliability

Nature of Correlation

• Association – an attempt to describe or understand

• Not causal– However, many people will use terms such as

“predictor”

Correlation

• Association between 2 variables in its simplest form.

• Variable X and Variable Y

• Often times X = predictor variableY = criterion variable

Predictor/Criterion

• Height and shoe size

.73

Height = predictor

Shoe size = criterion

Could very well be reversed - explanatory

Predictor/Criterion

• Predictor = High school GPA

• Criterion = College GPA

• Predictor = belief about fixed intelligence

• Criterion = amount of study time per week

• Predictor = amount of time reading at home

• Criterion = grades in Literacy in 8th grade

Coefficient of Determination

• Indicated by r2 (r-squared)

• Indicates the amount of variance explained or accounted by the relationship between the variables

• Quick and dirty method of understanding the strength of the relationship

Common uses in Education

• Validity (e.g. Criterion related: predictive & concurrent)

• Reliability of instruments

• Inter-rater reliability

Validity

How well can you defend the measure?

– Face V

– Content V

– Criterion-related V

– Construct V

Face Validity

• Does instrument look like valid?– On a survey or questionnaire, the questions

seem to be relevant– On a checklist, the behaviors seem relevant– For a performance test, the task seems to be

appropriate

Content Validity

• The content of the test, the measure, is relevant to the behavior or construct being measured

• An expert judges or a panel of experts judge the content

Criterion Related

• Using a another independent measure to validate a test– Typically computing a correlation

• Two types– Predictive validity– Concurrent validity

Criterion-Related

Predictive• ACT achievement test

Correlated with College GPA

Concurrent• Coopersmith Self-esteem Scale

Correlated with teacher’s ratings of self-esteem

Construct Validity

• Construct – attempt to describe, name an intangible variable

• Use many different measures to validate a measure

• Self-esteem – construct– Instrument measure

Construct Validity

• Self-esteem – construct– Instrument measure e.g. coopersmith

– Correlated it with:• Behavioral checklist• Teacher’s comments• Another accepted instrument for Self-esteem• A measure of confidence• Locus of control measure

Reliability

• For an instrument –– Consistency of scores from use to use

• Types of reliability coefficients– Test – retest– Equivalent forms– Internal consistency

• Split-half• Alpha coefficient (Cronbach alpha)

Reliability Coefficient

• Value ranges from 0 to +1.00

• .70 considered the minimal acceptable

• .90 is very good

• .60 is sometimes acceptable but is really not very good

• Lower than .60 definitely unacceptable

Reliable but is it Valid?Valid but is it Reliable?

Invalid and UnreliableNo confidence you’ll get near the target; have no idea where it’s going to shoot.

Reliable but is it Valid?Valid but is it Reliable?

Invalid but ReliableNo confidence you’ll get near the target; but you know where it’s going to shoot (just not at the target!)

Reliable but is it Valid?Valid but is it Reliable?

Valid but UnreliableConfidence that when you hit something, it’s what you want, but you can’t depend upon consistency.

Reliable but is it Valid?Valid but is it Reliable?

Valid and ReliableConfident that when you hit a target, it’s what you want and you can depend upon consistent shots.

Inter-rater reliability

Example –

Two teachers reading same essay, scoring them in a similar manner – consistently

Using same checklist to make observations

Can be expressed as a coefficient

Often as percentage of agreement

A function of training, objectivity, and rubric or checklist, i.e., the operational definition!

• Norm-referenced tests– Comparison of individual score to others– Intelligence test– ISAT, Iowa Basic Skills Test– SAT aptitude test– Personality test

– Percentile’s - derived scores– Grading on a curve

• Criterion referenced test– Individual score is compare to a benchmark (a

criterion)

– If Raw Score used (no conversion): C-R test– Mastery of material– Earning a grade in my class

– Disadvantage is potential lack of variability

Measures of Optimum Performance

• Aptitude Tests– Predict future performance

• Achievement tests– Measure current knowledge

• Performance tests– Measure current ability to complete tasks

Measures of typical performance

Often impacted by “social desirability”– Wanting to hide

undesirable traits or characteristics

One way to work around sd is touse projective tests

Rorschach ink Blot

Thematic Apperception Test

• Paper/pencil measures of attitudes using Likert-type scales

• Strongly Agree – Strongly Disagree- Reverse scoring to prevent or identify

“response bias”