spearbrown {CMO}R Documentation

Spearman Brown prediction formula

Description

Predicts the reliability of a psychometric test when the test length changes.

Usage

spearbrown(RelNow, LengthNow, LengthLater)

Arguments

RelNow reliability of the current test
LengthNow number of test items before the change
LengthLater number of test items after the change

Details

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.

Value

Predicted reliability of a psychometric test after the test length changed.

Author(s)

Christian Montel

References

Lienert and Raatz (1994) Testaufbau und Testanalyse. Weinheim: Beltz-PVU. p. 209f.

Examples

##---- Should be DIRECTLY executable !! ----

[Package CMO version 1.02 Index]