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Fig. 1 | BMC Medical Research Methodology

Fig. 1

From: A comparison of estimators from self-controlled case series, case-crossover design, and sequence symmetry analysis for pharmacoepidemiological studies

Fig. 1

Typical settings of analytical periods for the three self-controlled methods used in this study. a Self-controlled case series. The observation period of each subject is divided into risk periods (defined number of days after an exposure) and control periods (all other periods). b Case-crossover design. For each case, a case period (defined number of days before the first event) and a corresponding control period (defined number of days before the first event) are designated. (c) Sequence symmetry analysis. A crude sequence ratio is calculated by dividing the number of subjects who had experienced the first event a defined number of days after the first exposure (indicated by the black arrow, i.e., exposure ➔ event) by the number of subjects who had experienced the first event a defined number of days before the first exposure (indicated by the white arrow, i.e., event ➔ exposure)

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