2CHAPTER OBJECTIVES Define validity and reliability Understand the purpose for needing valid and reliable measuresKnow the most utilized and important types of validity seen in special education assessmentKnow the most utilized and important types of reliability seen in special education assessment
3VALIDITYDenotes the extent to which an instrument is measuring what it is supposed to measure.
4Criterion-Related Validity A method for assessing the validity of an instrument by comparing its scores with another criterion known already to be a measure of the same trait or skill.
5validity coefficient Criterion-related validity is usually expressed as a correlation betweenthe test in question and thecriterion measure. The correlationcoefficient is referred to as avalidity coefficient
6The extent to which a procedure correlates with the current CONCURRENT VALIDITYThe extent to which aprocedure correlateswith the currentbehavior of subjects
7PREDICTIVE VALIDITYThe extent to which a procedure allows accurate predictions about a subject’s future behavior
8CONTENT VALIDITYWhether the individual items of a test represent what you actually want to assess
9CONSTRUCT VALIDITY CONSTRUCT The extent to which a test measures a theoretical construct or attribute.CONSTRUCTAbstract concepts such as intelligence, self-concept, motivation, aggression and creativity that can be observed by some type of instrument.
10A test’s construct validity is often assessed by its convergent and discriminant validity.
11FACTORS AFFECTING VALIDITY Test-related factorsThe criterion to which you compare your instrument may not be well enough establishedIntervening eventsReliability
12The consistency of measurements RELIABILITYThe consistency of measurementsA RELIABLE TESTProduces similar scores across various conditions and situations, including different evaluators and testing environments.
13How do we account for an individual who does not get exactly the same test score every time he or she takes the test?Test-taker’s temporary psychological or physical stateEnvironmental factorsTest formMultiple raters
14RELIABILITY COEFFICIENTS The statistic for expressing reliability.Expresses the degree of consistency in the measurement of test scores.Donoted by the letter r with two identical subscripts (rxx)
15TEST-RETEST RELIABILITY Suggests that subjects tend to obtain the same score when tested at different times.
16Split-Half Reliability Sometimes referred to as internal consistencyIndicates that subjects’ scores on some trials consistently match their scores on other trials
17INTERRATER RELIABILITY Involves having two raters independentlyobserve and record specified behaviors,such as hitting, crying, yelling, and gettingout of the seat, during the same time periodTARGET BEHAVIORA specific behavior the observer is looking to record
18ALTERNATE FORMS RELIABILITY Also known as equivalent forms reliability or parallel forms reliabilityObtained by administering two equivalent tests to the same group of examineesItems are matched for difficulty on each testIt is necessary that the time frame between giving the two forms be as short as possible
19STANDARD ERROR of MEASUREMENT (SEM) OBTAINED SCOREThe score you get when you administer a testConsists of two parts: the true score and the error scoreSTANDARD ERROR of MEASUREMENT (SEM)Gives the margin or error that you shouldexpect in an individual test score because ofimperfect reliability of the test
20Evaluating the Reliability Coefficients The test manual should indicate why a certain type of reliability coefficient was reported.The manual should indicate the conditions under which the data were obtainedThe manual should indicate the important characteristics of the group used in gathering reliability information
21FACTORS AFFECTING RELIABILITY Test lengthTest-retest intervalVariability of scoresGuessingVariation within the test situation
22CHAPTER OBJECTIVES Define validity and reliability Understand the purpose for needing valid and reliable measuresKnow the most utilized and important types of validity seen in special education assessmentKnow the most utilized and important types of reliability seen in special education assessment