What is Reliability? * Consistency * It is not a characteristic of the test but a property of the scores obtained when the test is administered to a particular group of people on a particular occasion under specific conditions * Not the same thing as stability
Classical Reliability Theory * By Charles Spearman (1904) * Also called the Theory of true and error scores * It assumed that a person’s observed score on a test is composed of a “true” score plus some unsystematic error of measurement * TRUE SCORE – the average of the scores a person would obtain if he/she took the test an infinite number of times
2 Factors that influence test scores: * 1. Factors that contribute to consistency - consist of those stable attributes of the individual which the examiner is trying to measure (TRUE VARIANCE) * 2. Factors that contribute to inconsistency – these include the characteristics of the individual, test, or situation which have nothing to do with the attribute being measured but affects the scores (ERROR VARIANCE)
EQUATION:
* X = T + e * Where: * X is the obtained score * T is the true score * e is the errors of measurement * Errors in measurement –represent discrepancies b/n obtained scores and the corresponding true scores (E=X – T)
SOURCES OF MEASUREMENT ERROR (ERROR VARIANCES) * Item Selection(Intrinsic Error Variance) * Found in the instrument itself * Test items may not be equally fair to all persons * There maybe intrinsic elements of chance within the score of the testee * By accident, he/she knew items by chance or he/she does not know the items * 2. Extrinsic Error Variances (Internal or External)
A. Test Administration * Physical structure of the room * Motivation of the examinees * Style of the examiner
B. Test Scoring
MEASUREMENT ERROR & RELIABILITY * Measurement error reduces reliability or repeatability of psychological test results * Errors of measurement contribute to inconsistency of obtained scores; results will not remain stable if the test is administered again.
METHODS OF ESTIMATING RELIABILITY
1. RELIABILITY COEFFICIENT – indicates the extent to which individuals in a group maintain relatively consistent scores when two sets of measures are obtained and correlated using the same test or its equivalent forms.
2. STANDARD ERROR OF MEASUREMENT – an absolute reliability stated in terms of an estimate of the deviation of a set of obtained scores from their true scores
TYPES OF RELIABILITY
A. RELIABILITY AS MEASURES OF TEMPORAL STABILITY * Temporal Stability means consistency of responses to a measuring instrument over time * If the test is reliable, the second score is predictable based on his/her first score * If 2nd score is correlated with the 1st score, the test is reliable
1. TEST-RETEST RELIABILITY (test-retest coefficient) * Retest reliability shows the extent to which scores on a test can be generalized over different occasions * the higher reliability, the less susceptible the scores are to the random daily changes in the condition of examinees or testing environment * -coefficient of stability- tells how stable a particular performance is (Chronbach, as cited in )
2. PARALLEL-FORMS RELIABILITY (also called Alternative-Form Reliability) * Results to parallel forms coefficient * It is testing a person with one form on the first occasion, and with another equivalent form of the test on the next occasion