Sample size and study interpretation
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* Frank C. Leung

*   © 2004 Canadian Medical Association or its licensors

Max Pittler and associates1 report the results of a randomized double-blind crossover trial of the effectiveness of artichoke extract in preventing alcohol-induced hangovers. However, their sample size of 15 is too small. Even though the study had a crossover design, the standard deviations (SDs) are too large for the results to have statistical significance (e.g., mean systolic blood pressure of 124.3 with SD of 17.7 mm Hg and mean diastolic blood pressure of 75.4 with SD of 10.9 mm Hg at baseline). Furthermore, the range of blood pressure measurements (as derived from the means and standard deviations presented in the article) indicate that the volunteers were not all that healthy.

Another problem relates to the study's power. Pittler and associates1 state in the Methods section that there would be a power of 80% with 16 participants, but it is not clear if they recalculated the power on the basis of the 15 participants who actually completed the study. Also, the Methods section does not state the critical estimated scores of the 2 groups. The authors do admit a limitation relating to a possible type II error because of the small sample size. If this type II error was large, the authors are not justified in saying that “artichoke extract does not prevent the signs and symptoms of alcohol-induced hangover over and above placebo.”

**Frank C. Leung** Retired Division of Infection and Immunology Health Canada Toronto, Ont.

## Footnotes

*   Competing interests: None declared.

## Reference

1.  1. Pittler MH, White AR, Stevinson C, Ernst E. Effectiveness of artichoke extract in preventing alcohol-induced hangovers: a randomized controlled trial. CMAJ 2003;169(12):1269-73.
    
    [Abstract/FREE Full Text](http://www.cmaj.ca/lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6NDoiY21haiI7czo1OiJyZXNpZCI7czoxMToiMTY5LzEyLzEyNjkiO3M6NDoiYXRvbSI7czoyMzoiL2NtYWovMTcwLzgvMTIwNy4zLmF0b20iO31zOjg6ImZyYWdtZW50IjtzOjA6IiI7fQ==)