Treatment Control Total Died within 30-days a b a + b Alive at 30-days c d c + d Total a + c b + d N = a + b + c + d A 2x2 contingency table + marginal totals

Measure Formula Example Number needed to treat (NNT) = 1 ARR 1 0.1 = 10 Equivalent to the average number of patients who need to be treated to prevent one additional event

low baseline risk RR = OR 1 − AR=>?9:>@ + 1 − AR=>?9:>@ OR Source: Grant, R. L. (2014). Converting an odds ratio to a range of plausible relative risks for better communication of research findings. BMJ, 348(4), f7450.

Relative effect: HR = 0.55 Absolute effect: ARR(12-months) = 20.0% 30.7% in the TAVI group 50.7% in the standard therapy group NNT(12-months) = 5 • HR uses all data at each time point • Not robust to departures from proportionality

both * Naylor et al. Measured enthusiasm: does the method of reporting trial results alter perceptions of therapeutic effectiveness? Ann Intern Med. 1992; 117(11):916-21.