Objectives: To provide review authors with the knowledge and skills needed to calculate number needed to treat for an additional beneficial/harmful outcome (NNTB/NNTH) from trial reports and 'Summary of findings' (SoF) tables of Cochrane Reviews; to verify whether reported NNTB/Hs are adequate, and to interpret the results.

Description: The NNTB/H is widely used to present the results of clinical trials. However, incorrect calculations, misuse in specific study situations and misleading interpretation of NNTB/Hs are not uncommon in practice, for example in the case of non-significant results or in the situation of survival time data.

This workshop will provide an introduction to the use and interpretation of NNTB/Hs as effect measures in clinical trials and systematic reviews. We will show how to calculate NNTB/Hs with corresponding confidence intervals from SoF tables. We will discuss in particular the limitations of NNTB/Hs including problems associated with the inconvenient scale, the sensitivity to changes of the baseline risk and the dependence on the follow-up time.

Small group practical work will be an integral part of the workshop focusing on adequate calculation and interpretation of point and interval estimates of NNTB/Hs in practical examples. Participants should bring pocket calculators, pens and paper.