Refers to the consistency of a set of measurements when a testing procedure is repeated on a population of individuals or groupsoRandom or unsystematic errors: occurrence or degree of the error does not appear to be predictableoSystematic errors: the errors may be made in a consistent, or predictable fashion
oSystematic errors do not affect the accuracy of the measurements but rather the meaning or interpretation of those measurementsInterpreting reliability coefficientsoAnother way to think of reliability is in terms of the variability of a set of scoresoReliability can be thought of as the ratio of true score variance, Var(T), to observed score variance, Var(X)oo is the reliability coefficient, the degree that observed sores, which are made on the same stable characteristic, correlate with one anotherMeasurement erroroMeasurement error can be thought of as the hypothetical difference between an individual’s observed score on any particular measurement and the individual’s true scoreoMeasurement error, whether systematic or random, reduces the usefulness of any set of measures or the results from any testoIt reduces the confidence that we can place in the score the measure assigns to anyparticular individualoThe standard error of measurements is a statistical index that summarizes information related to measurement erroroThis index is estimated from observed scores obtained over a group of individualsoIt reflects how an individual’s score would vary, on average, over repeated observations that were made under identical conditionsFactors affecting reliabilityThe factors that introduce error into any set of measurements can be organized into three broad categories.oTemporary individual characteristicsoFactors such as health, motivation, fatigue, and emotional state introduce temporary, unsystematic errors into the measurement processoLack of standardizationoChanging the conditions under which measurements are made introduces error into the measurement processoCan be random or systematicoChanceoFactors unique to a specific procedure introduce error into the set of measurementsoChange factors produce unsystematic or random measurement errors
Methods of estimating reliabilityoTo measure reliability, we have to estimate the degree of variability in a set of scores that is caused by measurement erroroWe can obtain this estimate by using two different, but parallel, measures of the characteristic or attributeoOver the same set of people, both measures should report the same score for each individualoThis score will represent the true score plus measurement erroroBoth measures reflect the same true score; discrepancies between the two sets of scores suggest the presence of measurement erroroThe correlation coefficient based on the scores from both measures gives an estimate of rxx, the reliability coefficiento
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Psychology, researcher, investigator, measurement error, o Science