Dr Black raised the issue of the direction of the differences in the grand averages between piracetam and the placebo, which ignores both the psychological importance and statistical significance of the differences. His misunderstanding may have arisen because we converted the results to z-score values so all could be displayed in a single figure. This facilitated comparisons across measures but obscured the precise magnitude of the differences. While the mean differences may have favored piracetam over the placebo in some cases, the confidence intervals clearly indicate that an outcome in favor of the placebo was also possible. As we pointed out in the article, the largest difference between the 2 conditions was 0.55 SD, and this was found on the first trial of verbal learning. For this measure, the difference of 0.55 SD reflects a mean (± SD) of 2.89 (± 0.39) words recalled while taking piracetam compared with 2.06 (± 0.31) words recalled while taking the placebo. Finding 46 grand averages of this magnitude or smaller is not sufficiently compelling to conclude that piracetam use yielded more positive effects.
Lobaugh NJ, Koren G, Rovet J, Haslam R. Piracetam Study: Poorly Designed and Misinterpreted—Reply. Arch Pediatr Adolesc Med. 2001;155(10):1175–1176. doi:10.1001/archpedi.155.10.1175
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