Research and Statistics: Quantifying Associations: Understanding Relative Risks and Odds Ratios

Abstract

1. Katherine A. Connor, MD, MSPH 1. Johns Hopkins University, Baltimore, MD. * Abbreviations: aOR: : adjusted odds ratio OR: : odds ratio RR: : relative risk UTI: : urinary tract infection During a prenatal visit, the couple asks you about the risks and benefits of circumcision. They have heard that circumcised boys are less likely to get urinary tract infections (UTIs), but they want to understand how much the risk is decreased. In your literature search, you find this article: Craig JC, Knight JF, Sureshkumar D, et al. Effect of circumcision on incidence of urinary tract infection in preschool boys. J Peds . 1996;128(1):23–27. This is a case-control study (n = 886) designed to determine whether circumcision decreases the risk of symptomatic UTI in boys younger than 5 years of age. Participants were recruited from a large pediatric ambulatory center. The authors use odds ratios (ORs) to report their results. How can you use this information to help answer the family’s question? Relative risks (RRs) and ORs are measures used to quantify associations between an exposure and an outcome . In epidemiology texts, exposures generally are environmental or infectious, and outcomes may include death or development of disease. In clinical trials, the intervention being studied (eg, a medication) is the exposure, and the outcome is a specific clinical end point (eg, resolution of symptoms). When assessing associations between an exposure and an …