Huerta C, Rivero E, Rodriguez LA. Incidence and risk factors for psoriasis in the general population. Arch Dermatol. 2007 Dec;143(12):1559-65.
Reed (Earnshaw) SJ, Reed JH. The use of statistical quality control charts in monitoring interviewers. Proceedings of the Survey Research Methods Section, American Statistical Association. 1997 Jan;893-8.