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Questionnaire Development
Measuring Validity & Reliability James A. Pershing, Ph.D. Indiana University
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Definition of Validity
Instrument measures what it is intended to measure: Appropriate Meaningful Useful Enables a performance analyst or evaluator to draw correct conclusions
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Types of Validity Face Content Criterion Construct Concurrent
Predictive Construct
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Face Validity It looks OK
Looks to measure what it is supposed to measure Look at items for appropriateness Client Sample respondents Least scientific validity measure Looks Good To Me
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Content-Related Validity
Organized review of format and content of instrument Comprehensiveness Adequate number of questions per objective No voids in content By subject matter experts Balance Definition Sample Content Format
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Criterion-Related 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 Subject Instrument A Instrument B Task Observation Inventory Checklist John yes no Mary no no Lee yes no Pat no no Jim yes yes Scott yes yes Jill no yes Usually expressed as a correlation coefficient (0.70 or higher is generally accepted as representing good validity)
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Construct-Related Validity
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) Prediction 1 - Confirmed THEORY Prediction 2 - Confirmed Prediction 3 - Confirmed Prediction n - Confirmed
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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
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Types of Reliability Test-Retest Equivalent Forms Internal Consistency
Split-Half Approach Kuder-Richardson Approach Cronbach Alpha Approach
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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 of+.51 to +.75 moderate to good r over +.75 = very good to excellent T I M E
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Equivalent Forms Reliability
Also called alternate or parallel forms Instruments administered to same group at same time Vary: Calculate a reliability coefficient (r) to indicate the relationship between the two sets of scores. r of+.51 to +.75 moderate to good r over +.75 = very good to excellent Stem: -- Order -- Wording Response Set: -- Order -- Wording
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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
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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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