CD79A and acquired polycythemia vera: Although the study recruited a relatively large sample size of 42 patients with BP, 65 patients with PV, 50 patients with PF, 97 disease and 100 healthy control patients, the research was limited by a low case-to-control ratio (< 1:2) as well as hospital-based recruitment of control patients with other dermatological conditions such as linear IgA bullous dermatosis, vascular leg ulcers, basal cell carcinoma, and squamous cell carcinoma, which leads to a potential source of selection bias.