How to communicate effect sizes for continuous outcomes: a review of existing options and introducing a new metric

Abstract

Background and objective: Communicating the results of studies is an important problem. For binary outcomes, communication is relatively straightforward and supported by several statistical tools (e.g., the risk ratio and the number needed to treat [NNT]). For continuous outcomes, the situation is much worse. We discuss several alternatives and propose a new metric, NNTthreshold, that is analogous to the NNT statistic for binary outcomes and that is useful when a clinically meaningful threshold can be identified.

Method: We use both statistical theory and a statistical simulation to demonstrate how to compute NNTthreshold and to investigate how it behaves.

Results: NNTthreshold appears to function well, though is slightly conservative in our simulation.

Conclusion: Study authors need to think carefully about how to discuss study results when outcomes are continuously scaled. NNTthreshold should be helpful in situations in which a clinically meaningful threshold can be identified.

Keywords: Clinically meaningful; Communication; Effect size; Meta-analysis; NNT; Threshold.