instrument validity & reliability. why do we use instruments? reliance upon our senses for...

Instrument Validity

&Reliability

Why do we use instruments?

• Reliance upon our senses for empirical evidence

• Senses are unreliable

• Senses are imprecise – not valid enough – Operational definitions are important

Validity –

How much confidence do you have in the measurement of your instrument?

Reliability –

How consistent is your measurement?

How much confidence do you have?

Judgmental Validity

– Face V

– Content V

Empirical validity– Criterion-related V

• Predictive • Concurrent

Judgmental-Empirical

- 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 Validity

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

coefficient

• Two types– Predictive validity– Concurrent validity

Criterion-Related Validity

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

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.

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

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”