Additional file 1: of Evaluation of the impact of disease prevention measures: a methodological note on defining incidence rates Yin-Bun Cheung Ying Xu Matthew Cairns Paul Milligan 10.6084/m9.figshare.c.3749459_D1.v1 https://springernature.figshare.com/articles/journal_contribution/Additional_file_1_of_Evaluation_of_the_impact_of_disease_prevention_measures_a_methodological_note_on_defining_incidence_rates/4902479 “Time not at risk” and its approximation. Derivation of the equations for approximating time not at risk. (DOCX 33 kb) 2017-04-21 05:00:00 Incidence rate Prevention trials Protective efficacy Recurrent events