Statistical Power and the Rorschach: 1975-1991

Abstract
The Rorschach Inkblot Test has been the source of long-standing controversies as to its nature and its psychometric properties. Consistent with behavioral science research in general, the concept of statistical power has been entirely ignored by Rorschach researchers. The concept of power is introduced and discussed, and a power survey of the Rorschach literature published between 1975 and 1991 in the Journal of Personality Assessment, Journal of Consulting and Clinical Psychology, Journal of Abnormal Psychology, Journal of Clinical Psychology, Journal of Personality, Psychological Bulletin, American Journal of Psychiatry, and Journal of Personality and Social Psychology was undertaken. Power was calculated for 2,300 statistical tests in 158 journal articles. Power to detect small, medium, and large effect sizes was .13, .56, and .85, respectively. Similar to the findings in other power surveys conducted on behavioral science research, we concluded that Rorschach research is underpowered to detect the dif...

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