The Case Series Method: Performance and Design of Vaccine Safety

The self-controlled case series method (SCCSM) is a §novel study design to investigate associations §between acute responses with transient point §exposures (for example vaccination). The method §provides an attractive alternative to cohort and §case-control designs. The method is unusual in that §it requires data only on individuals who experience §a response (the cases ). The data are then analysed §using a Poisson model, conditional on the total §number of events occurring for each individual. This §conditioning ensures that including only cases does §not bias the relative risk estimator. The self-§controlled case series method has been used §to good effect in many settings, such as MMR vaccine §and autism, oral polio vaccine and intussusception, §MMR vaccine and idiopathic thrombocytopenic purpura, §influenza vaccine and asthma exacerbations. §However, hitherto, limited research had been §undertaken on the statistical properties of the §method in general, and virtually no work had been §undertaken on design issues. All these issues were §explored and consolidated by analysing data on §intussusception and oral polio vaccine from §GlaxoSmithKline (GSK).