Delta-p (Δp)

Δp is a statistic that is used to measure a relationship between two variables, and has been recommended as the measure to use in studies of contingency theory (Allan, 1980). It is defined for a two-way contingency table that provides the frequencies of a stimulus occurring (or not) when paired with a result (or not). In the table shown below, a, b, c and d are frequencies of occurrence for the four possible combinations of stimulus and result. The equation for Δp is given below the table.

Δp = (ad - bc)/[(a + b)(c + d)]

References:

1. Allan, L. G. (1980). A note on measurement of contingency between two binary variables in judgment tasks. Bulletin of the Psychonomic Society, 15(3), 147-149.