The description and analysis of conditioned suppression: A critique of the conventional suppression ratio

Abstract

It is argued that the conventional A/(A+B) ratio is an inappropriate tool for both the description and analysis of conditioned suppression. Conditioned suppression is a procedure that generates two separate dependent variables that cannot be meaningfully collapsed into a single index. Using a relatively simple experiment, we demonstrate that the procedure typically (1) suppresses responding during the CS and (2) generates a U-shaped function in the recovery of baseline responding. These reliable shifts in baseline rate confound the interpretation of the suppression ratio. It is further argued that comparison between individuals or groups of cases using an analysis of variance performed on suppression ratios is inappropriate because of numerous violations of the assumptions of the test. We offer a number of alternative strategies for the description and analysis of conditioned suppression. These include the use of raw data analyzed with nonparametric tests or an analysis of covariance, a procedure that accommodates the need for ipsative measurement without producing the flaws inherent in ANOVAs performed on suppression ratios. © 1983 Psychonomic Society, Inc.