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To the Editor:—
Herbert and Movius (JAMA187:767 [March 7] 1964) claim that mitral commissurotomy is not necessarily followed by psychological deficit. In their study, patients took psychological tests before, and five weeks after, commissurotomy, with no significant differences in the results. It was therefore concluded that central nervous system damage did not occur to a detectable degree in these patients. However, omission of a control group renders the significance of this finding moot, since a control group may very well have demonstrated the frequently described practice effect increment (improvement brought about by familiarity with the tests).In our studies of psychiatric patients, the mean Wechsler-Bellevue intelligence quotient did not change after five weeks of chlorpromazine administration, but the placebo group showed a markedly significant sevenpoint practice effect increment after five weeks, thus indicating that chlorpromazine was actually causing a defect. Similarly, the absence of a practice effect in
Klein DF, Pollack M. CNS Effects of Mitral Commissurotomy. JAMA. 1964;188(11):1017. doi:10.1001/jama.1964.03060370073031
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