title: Brief Report: Estimating Differences and Ratios in Median Times to Event.
abstract: Time differences and time ratios are often more interpretable estimates of effect than hazard ratios for time-to-event data, especially for common outcomes. We developed a SAS macro for estimating time differences and time ratios between baseline-fixed binary exposure groups based on inverse probability-weighted Kaplan-Meier curves. The macro uses pooled logistic regression to calculate inverse probability of censoring and exposure weights, draws Kaplan-Meier curves based on the weighted data, and estimates the time difference and time ratio at a user-defined survival proportion. The macro also calculates the risk difference and risk ratio at a user-specified time. Confidence intervals are constructed by bootstrap. We provide an example assessing the effect of exclusive breastfeeding during diarrhea on the incidence of subsequent diarrhea in children followed from birth to 3 years in Vellore, India. The SAS macro provided here should facilitate the wider reporting of time differences and time ratios.
authors.affiliation: From the aDepartment of Epidemiology, University of North Carolina at Chapel Hill, Chapel Hill, NC; bDivision of Gastrointestinal Sciences, Christian Medical College, Vellore, India; and cDivision of Geographic Medicine and Infectious Diseases, Tufts Medical Center, Boston, MA.
authors.forename: Elizabeth T
authors.initials: ET
authors.lastname: Rogawski
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Westreich
authors.forename: Gagandeep
authors.initials: G
authors.lastname: Kang
authors.forename: Honorine D
authors.initials: HD
authors.lastname: Ward
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Cole
mesh_terms: D001942:Breast Feeding; D002675:Child, Preschool; D016001:Confidence Intervals; D003627:Data Interpretation, Statistical; D003967:Diarrhea / Q000453:epidemiology / Q000517:prevention & control; D015340:Epidemiologic Research Design; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D007194:India / Q000453:epidemiology; D007223:Infant; D007231:Infant, Newborn; D053208:Kaplan-Meier Estimate; D008297:Male; D016017:Odds Ratio; D065840:Protective Factors; D012008:Recurrence; D055502:Secondary Prevention / Q000379:methods; D013995:Time