Questionnaire Development Measuring Validity & Reliability

James A. Pershing, Ph.D.

Indiana University

Definition of Validity

  Instrument measures what it is intended to measure:    Appropriate Meaningful Useful Enables a performance analyst or evaluator to draw correct conclusions

Types of Validity

    Face Content Criterion   Concurrent Predictive Construct

Face Validity

Looks Good To Me     It looks OK Looks to measure what it is supposed to measure Look at items for appropriateness  Client  Sample respondents Least scientific validity measure

Content-Related Validity

Balance Definition Sample Content Format   Organized review of format and content of instrument   Comprehensiveness Adequate number of questions per objective  No voids in content By subject matter experts

Criterion-Related Validity

Subject Instrument A Instrument B

Task Observation Inventory Checklist John Mary Lee yes no yes no no no Pat Jim Scott Jill no yes yes no no yes yes yes Usually expressed as a correlation coefficient (0.70 or higher is generally accepted as representing good validity)    How one measure stacks-up against another  Concurrent = at same time  Predictive = now and future Independent sources that measure same phenomena Seeking a high correlation

T H E O R Y

Construct-Related Validity

Prediction 1 - Confirmed Prediction 2 - Confirmed Prediction 3 - Confirmed Prediction n - Confirmed

   A theory exists explaining how the concept being measured relates to other concepts Look for positive or negative correlation Often over time and in multiple settings Usually expressed as a correlation coefficient (  0.70 or higher is generally accepted as representing good validity)

Definition of Reliability

  The degree to which measures obtained with an instrument are consistent measures of what the instrument is intended to measure Sources of error   Random error = unpredictable error which is primarily affected by sampling techniques  Select more representative samples  Select larger samples Measurement error = performance of instrument

Types of Reliability

   Test-Retest Equivalent Forms Internal Consistency   Split-Half Approach Kuder-Richardson Approach  Cronbach Alpha Approach

Test-Retest Reliability

  Administer the same instrument twice to the same exact group after a time interval has elapsed.

Calculate a reliability coefficient ( r ) to indicate the relationship between the two sets of scores.

  r r of+.51 to +.75 moderate to good over +.75 = very good to excellent

T I M E

Equivalent Forms Reliability

   Also called alternate or parallel forms Instruments administered to same group at same time Vary: Response Set: -- Order -- Wording Stem: -- Order -- Wording  Calculate a reliability coefficient ( r ) to indicate the relationship between the two sets of scores.

  r r of+.51 to +.75 moderate to good over +.75 = very good to excellent

Internal Consistency Reliability

  Split-Half Break instrument or sub parts in ½ -- like two instruments Correlate scores on the two halves Best to consult statistics book and consultant and use computer software to do the calculations for these tests  Kuder-Richardson (KR) Treats instrument as whole  Compares variance of total scores and sum of item variances   Cronbach Alpha Like KR approach Data scaled or ranked

Reliability and Validity

So unreliable as to be invalid Fair reliability and fair validity Fair reliability but invalid Good reliability but invalid Good reliability and good validity The bulls-eye in each target represents the information that is desired. Each dot represents a separate score obtained with the instrument. A dot in the bulls-eye indicates that the information obtained (the score) is the information the analyst or evaluator desires.

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