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PSYCHOMETRIC PROPERTIES OF QUANTITATIVE MEASURES Reliability and Validity of Test Measures Deciding what test to use Psychometric Properties Ease of Administration Training Needed Cost Appropriateness for your Population Definitions Reliabilityconsistent, reproducible, dependable Validitymeasures what it says it measures Reliability Measurement Error Reliability Coefficients Types of Reliability Test-retest Rater: Intra & Inter Internal Consistency Measurement Error Observed score = true score + error Measurement Error = true score – observed score Reliability estimates measurement error Sources of Measurement Error Systematic- consistently wrong in the same amount Random- chance rater measuring instrument variability in what you are measuring Reliability Coefficients True score variance True score variance + error variance as error decreases, coefficient increases coefficient ranges from .00 to 1.00 < .50 poor .50 to .75 moderate > .75 good Types of Reliability: Test-Retest Get the same results every time you use the test Intervals between testing- long enough to avoid fatigue or remembering the answers but not so long that natural maturation occurs Intraclass correlation coefficient (ICC) or Pearson r Another way to Test- Retest Alternate forms: different versions covering the same content (SAT, GRE) r correlation coefficient is used (.8 or higher) Types of Reliability: Internal Consistency Are all questions measuring the same thing? Split-half: correlation of two halves of same test (odds and evens) Spearman-Brown prophecy Cronbach’s alpha: essentially an average of the all the possible split-half reliabilities, can be used on multiple choice. When used on dichotomous scores, called KuderRichardson 20 Types of Reliability: Raters Intra – rater: stability of one rater across trials Inter-rater: consistency between two raters Use ICC for both types Validity Validity vs. Reliability Types of Validity Validity vs. Reliability not valid not reliable valid? not reliable not valid reliable valid reliable Generalizability External validity- the test is valid if used with the intended population The test is valid if used in appropriate context and as directed for its given purpose Face Validity appears to test what it is supposed to measure weakest form ok for ROM, length, observation of ADLs Content Validity covers the entire range of the variable and reflects the relative importance of each part based on expert opinion, needs to be free of cultural bias Test of function- 20 questions on brushing your teeth, 1 question each on mobility, bathing, dressing VAS vs. McGill Pain Questionnaire Criterion-related Validity target test compared to gold standard concurrent target test is taken at the same time as another test with established validity predictive examines whether the target test can predict a criterion variable Construct Validity ability of a test to measure a construct based on a theoretical framework what would you include for a test on “wellness”? Ways to establish construct validity Known groups Convergent comparison Divergent comparison Factor analysis Remember The reliability and validity of a test measurement is not the same thing as reliability and validity of a research design. Where do I find this information? lsustudent.pbworks.com/Psy Assessments Journals Books Test Manuals