spearbrown {CMO} | R Documentation |
Predicts the reliability of a psychometric test when the test length changes.
spearbrown(RelNow, LengthNow, LengthLater)
RelNow |
reliability of the current test |
LengthNow |
number of test items before the change |
LengthLater |
number of test items after the change |
This formula is commonly used by psychometricians to predict the reliability of a test after changing the test length. This relationship is particularly vital to the split-half and related methods of estimating reliability. The formula is also helpful in understanding the nonlinear relationship between test reliabilit and test length. If the longer/shorter test is not parallel to the current test, then the prediction will not be strictly accurate. For example, if a highly reliable test was lengthened by adding many poor items then the achieve reliability will probably be much lower than that predicted by this formula.
Predicted reliability of a psychometric test after the test length changed.
Christian Montel
Lienert and Raatz (1994) Testaufbau und Testanalyse. Weinheim: Beltz-PVU. p. 209f.
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