Self-controlled case-series analysis

The self-controlled case-series analysis only uses the patients in the cohort who have the outcomes of interest.²⁰ Cases with each type of AE will be identified; these will be cases with a diagnosis of the AE since 1 January 1998, who had a new diagnosis of depression (see above for details). Information on prescriptions for antidepressants in these cases will be extracted and the analysis (such as conditional fixed-effects Poisson regression model) will compare rates of the outcomes of interest in periods following a first prescription for an antidepressant compared with a baseline period free of antidepressant treatment for the same patient.²¹ We will account for multiple periods of exposure in the analysis, defining a period of antidepressant treatment as one without gaps of more than 30 days between the end of a prescription and the start of the next prescription. A prescription after more than 30 days will count as a new treatment episode. The 28 days before the first prescription in each treatment period will be considered separately, as occurrence of the outcome of interest in this period could affect the probability of an antidepressant prescription. All other time periods outside these specified risk periods will contribute to the baseline person time, that is, the unexposed periods.