Ellen Drost
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Reliability
Reliability is a major concern when a psychological test is used to measure some attribute or behaviour (Rosenthal and Rosnow, 1991). For instance, to understand the functioning of a test, it is important that the test which is used consistently discriminates individuals at one time or over a course of time. In other words, reliability is the extent to which measurements are repeatable –when different persons perform the measurements, on different occasions, under different conditions, with supposedly alternative instruments which measure the same thing. In sum, reliability is consistency of measurement (Bollen, 1989), or stability of measurement over a variety of conditions in which basically the same results should be obtained (Nunnally, 1978).