While most validity indices are based on total test scores, this paper describes a method for quantifying the construct validity. The approach is based on the item selection technique originally described by Piazza (1980). However, Piazza's P2 index suffers from some substantial limitations. The Dh coefficient provides an alternative that can be used for item selection and also to provide a validity index for a set of items. An example of how to use the technique is provided. This method may be especially useful when the sample of items and/or persons is small, rendering more traditional approaches such as factor analysis or item response theory inappropriate.
