Over the last decade a large body of epidemiological, translational, and animal model research has suggested that psoriasis may be a risk factor for cardiovascular and metabolic disease. Outcome based studies often suggest that patients with more severe psoriasis have an increased risk of major cardiovascular events independent of traditional risk factors that are captured in electronic health data. The study by Parisi and colleagues finds that incident severe psoriasis is associated with a non-statistically significant increased risk of major cardiovascular events, HR 1.28 (95% CI 0.96-1.69) in their primary model and a statistically significant increased risk, HR 1.46 (95% CI 1.11, 1.92), in a sensitivity analysis that excludes patients with inflammatory arthritis. These results are usefully consistent with prior studies published using the same or similar databases. Here we review three key biostatistical and epidemiological principles that are commonly misunderstood (over reliance on P-values, confounding versus effect modification, and inception versus prevalent cohort design) and often lead to controversy in analyzing and interpreting results.