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Reliability and Validity of Measures.docx

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Wilfrid Laurier University
Roger Buehler

ReliabilityandValidityofMeasuresTwo characteristics a measure has to have is reliability and validityReliability of a MeasureReliability refers to the consistency or dependability of a measurehow consistently a measure assigns the same score to the same observationExample Measuring HeightReliability As a Low measurement ErrorEvery score on a measure consists of two componentsObserved ScoreTrue ScoreMeasurement Error the two componentsTrue score the score if the measure were perfectError the result of factors that distort the observed score so that it differs from the true score Sources of Measurement ErrorAny factor that will influence where a person scored on the measure that isnt reflecting their true scoretrue ability Transient states of participantTired bad mood anxiousStable attributes of participantMotivation level intelligence Situational factors in research settingResearchers behavior room temperatureCharacteristics of measure itselfAmbiguous questions length of testMistakes in recordingData entry errors misperceptionReliability as a systematic varianceTotal variance in a set of scoresvariance due to true scoresvariance due to measurement errorReliabilitytrue score variancetotal varianceReliability is the proportion of the total variance in a set of scores that is associated with participants true scoresTo assess reliability we estimate the proportion of the total variance in the data that is truescore variance Assessing the reliability of measures Testretest reliabilityRefers to consistency over timeGive the same measure to participants on two or more occasionsAre scores at different times highly correlatedie is rank order of participants similar at each time pointUseful for stable attributes Abilities personality traits attitudesThe correlation coefficientonly one correlation run only one correlation coefficient comparing the correlation between the first scores and the second scores A statistic that indicates the degree of relation between two variablesMost common is the Pearson correlation coefficient rVaries from 10 to 10Indicates two things
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