V0b Relative Risk Cutoffs for Statistical Significance  2014

Abstract: Relative risks are often presented in the everyday media but are seldom mentioned in introductory statistics courses or textbooks. This paper reviews the confidence interval associated with a relative risk ratio. Statistical significance is taken to be any relative risk where the associated 90% confidence interval does not include unity. The exact solution for the minimum statistically-significant relative risk is complex. A simple iterative solution is presented. Several simplifications are examined. A Poisson solution is presented for those times when the Normal is not justified. 1. Relative risk in the everyday media In the everyday media, relative risks are presented in two ways: explicitly using the phrase “relative risk” or implicitly involving an explicit comparison of two rates or percentages, or by simply presenting two rates or percentages from which a comparison or relative risk can be easily generated. Here are some examples (Burnham, 2009): the risk of developing acute non-lymphoblastic leukaemia was seven times greater compared with children who lived in the same area, but not next to a petrol station Bosch and colleagues ( p 699) report that the relative risk of any stroke was reduced by 32 % in patients receiving ramipril compared with placeb