He. Barbaree et Djk. Mewhort, THE EFFECTS OF THE Z-SCORE TRANSFORMATION ON MEASURES OF RELATIVE ERECTILE RESPONSE STRENGTH - A REAPPRAISAL, Behaviour research and therapy, 32(5), 1994, pp. 547-558
In studies of stimulus control of sexual arousal, some researchers tra
nsform raw data to z-scores. Earls, Quinsey and Castonguay [Archives o
f Sexual Behavior, 16, 493 500 (1987)] have argued that the proportion
of variance due to stimulus presentations was greater in z-scores tha
n in the raw data or in a percent score. We present analyses of sexual
arousal data that show that z-score transformations may distort the i
nformation inherent in the raw data and may increase random error. In
addition, we present Monte Carlo analyses indicating that the z-score
transformation compromises the estimates of Type I error, and, dependi
ng on specific circumstances, sometimes increases and sometimes decrea
ses the power of the statistical test. Transformation of raw data to p
ercent of full erection does not distort the information in the raw da
ta, does not compromise the data analyses and, therefore, is the prefe
rred transformation.