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Encyclopedia Entry

Split-Half Reliability

Stuart J. McKelvie

In classical test score theory, X = T + e (where X = observed score, T = true score, and e = error). Some error is constant, reducing test validity, and some is variable, leading to inconsistency of scores. Reliability is the degree to which the test is free from variable error. Formally, given that σ 2 x = σ 2 1 + σ 2 1 , reliability is the ratio of true score variance to error score variance: Because they are necessarily a sample from the domain being measured, test items constitute one source of variable error. It can be estimated by comparing scores from two equivalent (alternate) forms of the test given at different times, but performance on the second test may be affected by the first one. Split-half reliability requires only one test administration, so participants are unaware of any comparison. It is obtained by splitting the ...

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