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August 16, 2016

Expanded Explanation of the Sample Size Calculation

JAMA. 2016;316(7):775. doi:10.1001/jama.2016.9458

In the Preliminary Communication entitled “Effect of Dexmedetomidine Added to Standard Care on Ventilator-Free Time in Patients With Agitated Delirium: A Randomized Clinical Trial” published in the April 12, 2016, issue of JAMA,1 the authors would like to expand on the explanation of the sample size calculation. In the 15th paragraph in the Methods section, the first sentence should be “Based on a pilot study with a mean control estimate of 108 ventilator-free hours (SD, 46 ventilator-free hours) and a mean dexmedetomidine group estimate of 148 ventilator-free hours (SD, 15 ventilator-free hours),12 a sample size of 96 patients was estimated to provide 80% power to detect a 20-hour difference (ie, half the effect size observed in the pilot study) using a 2-tailed hypothesis at an α level of .05.” This article was corrected online.

Reade  MC, Eastwood  GM, Bellomo  R,  et al; DahLIA Investigators; Australian and New Zealand Intensive Care Society Clinical Trials Group.  Effect of dexmedetomidine added to standard care on ventilator-free time in patients with agitated delirium: a randomized clinical trial.  JAMA. 2016;315(14):1460-1468.PubMedArticle