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To the Editor:—
Dr. Jarvik does no more than make general statements about the necessity of a control group in an experiment like ours. He cites no objective data to support the assertion that "effects of practice are manifested almost universally...." David Wechsler, author of the Wechsler Adult Intelligence Scale (WAIS), stated to me personally in 1960 that one reason he did not make two forms of the WAIS was that the items had been shown by experiment not to be affected by practice in a hospital population. In the new revision of the Stanford-Binet, it is pointed out that insignificant practice effects were found when the same form was used for retesting; therefore, the new revision came out in only one form.Further, the word "practice" implies that some learning is taking place. Impairment of learning is only one of the signs of malfunction which one looks for in
Herbert CT. CNS Effects or Mitral Commissurotomy. JAMA. 1964;189(7):587. doi:10.1001/jama.1964.03070070059023
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