where A denotes lack of presence of pattern A. Risk ratio shows the relative risk of
belonging to class C. Each rule was defined based on a list of parameters used for the
classification. These parameters were extracted based on the linked data (the same
data used by He et al. [2004]) and included patient-specific features such as age and
gender and drug-specific features. Patients were considered if they had taken a specific
drug of interest in a time window of 180 days.