The study was for retrospective data analysis only. Standard case-control methods were used. In most instances, multivariate analysis was used to control confounding, especially by simultaneous use of other causal drugs. Adverse effects and the relative safety of drugs in relation to the two dyscrasias were documented. Because the IAAAS was population-based, incidence rates were provided directly, and excess risks were estimated for associated drugs. Such quantitative measures of association were generally unavailable. Among the drugs that were analyzed were various categories such as psychotropics, antihistamines, and cardiovascular drugs, and individual drugs such as allopurinol. Factors other than drugs were also evaluated, including exposure to radiation and chemicals such as benzene and insecticides, history of viral infection, and history of allergy and other conditions.