Reliability of measurement in psychology: From Spearman-Brown to maximal reliability.

The authors extend the usual approach to the assessment of test or rater reliability to situations that have previously not been appropriate for the application of this standard (Spearman-Brown) approach. Specifically, the authors (a) provide an accurate overall estimate of the reliability of a test (or a panel of raters) comprising 2 or more different kinds of items (or raters), a quite common situation, and (b) provide a simple procedure for constructing the overall instrument when it comprises 2 or more kinds of items, judges, or raters, each with its own costs and its own reliabilities.