Superiority of Form% Over Lambda for Research on the Rorschach Comprehensive System Gregory J. Meyer Department of Psychology University of Alaska Anchorage Donald J. Viglione California School of Professional Psychology San Diego, California John E. Exner, Jr. Rorschach Workshops Asheville, North Carolina Lambda is an important variable in the Rorschach Comprehensive System. However, because of the way it is calculated it has properties that can produce problems for parametric statistical analyses. We illustrate these difficulties and encourage the use of Form% (i.e., pure form responses/total responses) instead of Lambda in research. Form% is easy to calculate, and it is conceptually and mathematically comparable to Lambda. Because it is much more normally distributed, Form% is suitable to use in parametric analyses (e.g., t tests, analyses of variance, correlations, factor analyses, multiple regressions). Lambda is a key variable in the Rorschach Comprehensive System (CS). It is calcu- lated as the ratio of pure form responses to nonpure form responses. Specifically, Lambda = F/(R – F), where F indicates the number of pure form responses, and R indicates the total number of responses. Lambda has a long history in Rorschach scoring (see Exner, 1993), and it is frequently interpreted as a dichotomous variable that indicates the tendency to simplify complex stimulus fields (i.e., Lambda > 0.99) or not (i.e., Lambda < 1.0). As a dichotomous variable, Lambda can be used in many nonparametric statistical analyses (e.g., chi-square tests, median tests, sign JOURNAL OF PERSONALITY ASSESSMENT, 76(1), 68–75 Copyright © 2001, Lawrence Erlbaum Associates, Inc.