Measurement of psoriasis disease severity and effectiveness of treatment involves both objective and subjective assessments.1 Comparing the efficacy of different treatments is complicated by the use of different metrics for measuring outcomes.2 Because these measures are not used routinely in clinical practice, interpreting these data, in particular assessing the degree of clinically meaningful improvement, is difficult. The drug approval process and product labeling reflect historical changes in standards of efficacy measurement.3 This paper reviews the metrics used to evaluate psoriasis treatment and compares available information on approved treatments for severe psoriasis. It further attempts to elucidate the value of these metrics and provide some guidance in properly evaluating the relative efficacy of current proven therapy with new treatments. While clinical trials are somewhat artificial, they provide proof that a drug is more effective than placebo. Efficacy in clinical practice, however, may be very different from the clinical trial setting. Comparison of efficacy under the current circumstances of varying evaluative metrics scales is possible with proper knowledge of the functionality of these methods.