In this issue of JAMA Facial Plastic Surgery, Sapthavee et al1 present a retrospective cohort study designed to compare the effectiveness of skin graft reconstruction and local flap reconstruction for nasal defects. This article is an excellent example of how level of evidence (LOE) can be increased from level 4 (case series) to level 3 (retrospective cohort study) by adding a comparison cohort group to the analysis (Table 1).2 It is also a good example of using a nonparametric statistical test, the Wilcoxon rank sum test, to evaluate nonparametric data.
Ishii LE. Thoughtful Methods to Increase Evidence Levels and Analyze Nonparametric Data. JAMA Facial Plast Surg. 2015;17(4):307-308. doi:10.1001/jamafacial.2015.0465