WhaT is cOmparaTiVe eFFecTiVeness research.... and WhY dO iT? Comparative effectiveness research (CER) aids clinicians faced with medical decision making by identifying the best strategies among a variety of available preventive, diagnostic, and treatment options. Differing from early-phase clinical trials—in which an intervention is compared with a placebo and assessed for efficacy—the goal of CER is to discriminate among clinical interventions on the basis of clinical effectiveness, cost-effectiveness, adverse effects, or other distinguishing factors. As part of the American Recovery and Reinvestment Act of 2009, the US government allocated $1.1 billion for the funding of CER with two primary aims: “(1) to conduct, support, or synthesize research that compares the clinical outcomes, effectiveness, and appropriateness of items, services, and procedures that are used to prevent, diagnose, or treat diseases, disorders, and other health conditions; and (2) encourage the development and use of clinical registries, clinical data networks, and other forms of electronic health data that can be used to generate or obtain outcomes data” (Department of Health and Human Services, http:// www.hhs.gov/recovery/programs/cer/index.html, accessed 15 September 2012). One motivation behind the funding of CER is stimulating the delivery of higher-quality health care in a more cost-effective manner. Through well-designed and executed studies, CER has the potential to greatly enhance the practice of evidence-based dermatology (Williams, 2011). Common methodological approaches to conducting CER include randomized controlled trials and systematic reviews. This article will review recent examples of CER study designs in the dermatology literature as well as statistical analyses used to interpret such designs.