In their recent article, Elewski et al1 conclude that the "use of 15% azelaic acid gel twice daily for 15 weeks demonstrated significant superiority over using 0.75% metronidazole gel in improving principal signs of rosacea (inflammatory lesions and erythema)." This conclusion was based on differences in mean inflammatory lesion count reductions at the last observation carried forward: 12.9 mean inflammatory lesion count reduction for azelaic acid vs a 10.7 reduction for metronidazole (Δ = 2.2). At week 15, the difference was 13.6 for azelaic acid vs 11.8 for metronidazole (Δ = 1.8). However, in the "Methods" section it is stated, "A difference of 5 lesions in mean lesion count for the 2 treatments was considered to be medically relevant" and the sample size was calculated to detect this difference of Δ = 5 with a power of 80%. Thus, the observed difference (Δ = 2.2) was statistically significant but power of the test was below 80%.
Czernielewski J, Liu Y. Comparison of 15% Azelaic Acid Gel and 0.75% Metronidazole Gel for the Topical Treatment of Papulopustular Rosacea. Arch Dermatol. 2004;140(10):1282-1283. doi:10.1001/archderm.140.10.1282-b