Related Experiment Video
Updated: May 10, 2026

Inverse Probability of Treatment Weighting (Propensity Score) using the Military Health System Data Repository and National Death Index
Published on: January 8, 2020
Absolute risks rather than incidence rates should be used to estimate the number needed to treat from time-to-event
Ralf Bender1, Mandy Kromp, Corinna Kiefer
1Department of Medical Biometry, Institute for Quality and Efficiency in Health Care, Im Mediapark 8, D-50670, Cologne, Germany. Ralf@rbsd.de
Background:
When estimating the number needed to treat (NNT) from randomized controlled trials (RCTs) with time-to-event outcomes, varying follow-up times have to be considered. Two methods have been proposed, namely (1) inverting risk differences estimated by survival time methods (RD approach) and (2) inverting incidence differences (ID approach).
Study Design And Setting:
A simulation study was conducted to compare the RD and the ID approaches regarding bias and coverage probability (CP) considering various distributions, baseline risks, effect sizes, and sample sizes. Additionally, the two approaches were compared by using two real data examples.
Results:
The RD approach showed good estimation and coverage properties with only a few exceptions in the case of small sample sizes and small effect sizes. The ID approach showed considerable bias and low CPs in most of the considered data situations.
Conclusions:
Absolute risks estimated by means of survival time methods rather than incidence rates should be used to estimate NNTs in RCTs with time-to-event outcomes.
Related Concept Videos
Relative Risk
Types of Biopharmaceutical Studies: Controlled and Non-Controlled Approaches
Non-controlled studies, commonly employed for initial exploration, lack a control group, rendering them susceptible to biases and external influences. In contrast, controlled...
Kaplan-Meier Approach
Actuarial Approach
Consider the example of a high-risk surgical procedure with significant early-stage mortality. A two-year clinical study is conducted,...
Assumptions of Survival Analysis
Hazard Rate

