Subject bias and the retrospective pretest in retrospect

Abstract

Studies employing designs including a thentest were reviewed to examine to what extent they demonstrated a response shift, while controlling for subject bias by including a placebo control condition. A computer search was executed to detect articles that included the Howard, Ralph, et al. (1979) article in their reference list. Of 24 studies, 16 did not warrant any statement about the occurrence of a response-shift bias, relative to a subject bias, because they lacked a placebo control condition. Support for the subject bias hypothesis, relative to the response-shift hypothesis, was found in one of eight studies that did include a placebo control condition. With respect to these results, three supplementary considerations were taken into account. It was concluded that subject bias has not proved to be an unqualified alternative explanation of the response-shift interpretation in the reported studies. © 1989, The Psychonomic Society, Inc.. All rights reserved.