Superiority of form% over Lambda for research on the Rorschach Comprehensive System

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).