Reply: Topical Silicone Gel versus Placebo in Promoting the Maturation of Burn Scars: A Randomized Controlled Trial—The Pivotal Role of Statistics

Abstract

Sir: We agree with Dr. Mangano that an accurate experimental design is essential for drawing valid conclusions from any clinical trial and that the required sample size should be calculated and fixed before starting a trial. We did perform an a priori sample size calculation but unfortunately this was not mentioned in the article. Based on data from previous studies, a difference in redness scores at follow-up of approximately the size of the score's standard deviation was anticipated. Comparing the follow-up measurements under the two conditions using a standard t test would then require 36 scars to be treated and evaluated (18 per treatment) to achieve 80 percent power when tested two-sided at a significance level 5 percent. To further increase power, an intraindividual comparison design was used in which subjects with two comparable scars were included. One of these scars was treated with silicone gel and the other was treated with the placebo cream. Based on the power analyses, the aim was to include 25 patients (50 scars) to correct for possible dropout. At the end of the inclusion period, 23 patients were included, which was considered to be sufficient. Martijn B. A. van der Wal, M.D. Burn Center Red Cross Hospital Beverwijk, The Netherlands Association of Dutch Burn Centers Beverwijk, The Netherlands Department of Plastic, Reconstructive, and Hand Surgery, VU University Medical Center Amsterdam, The Netherlands Paul P. van Zuijlen, M.D., Ph.D. Burn Center and Department of Plastic, Reconstructive, and Hand Surgery Red Cross Hospital Beverwijk, The Netherlands Association of Dutch Burn Centers Beverwijk, The Netherlands Department of Plastic, Reconstructive, and Hand Surgery, VU University Medical Center Amsterdam, The Netherlands Peter van de Ven, Ph.D. Department of Epidemiology and Biostatistics VU University Medical Center Amsterdam, The Netherlands Esther Middelkoop, Ph.D. Association of Dutch Burn Centers Beverwijk, The Netherlands Department of Plastic, Reconstructive, and Hand Surgery VU University Medical Center Amsterdam, The Netherlands