### 9.4.9 Meta-analysis of time-to-event outcomes

Two approaches to meta-analysis of time-to-event outcomes are available in RevMan. Which is used will depend on what data have been extracted from the primary studies, or obtained from re-analysis of individual patient data.

If ‘O – E’ and ‘V’ statistics have been obtained, either through re-analysis of individual patient data or from aggregate statistics presented in the study reports, then these statistics may be entered directly into RevMan using the ‘O – E and Variance’ outcome type. There are several ways to calculate ‘O – E’ and ‘V’ statistics. Peto’s method applied to dichotomous data (Section 9.4.4.2) gives rise to an odds ratio; a log-rank approach gives rise to a hazard ratio, and a variation of the Peto method for analysing time-to-event data gives rise to something in between. The appropriate effect measure should be specified in RevMan. Only fixed-effect meta-analysis methods are available in RevMan for ‘O – E and Variance’ outcomes.

Alternatively if estimates of log hazard ratios and standard errors have been obtained from results of Cox proportional hazards regression models, study results can be combined using the generic inverse-variance method (see Section 9.4.3.2). Both fixed-effect and random-effects analyses are available.

If a mixture of log-rank and Cox model estimates are obtained from the studies, all results can be combined using the generic inverse-variance method, as the log-rank estimates can be converted into log hazard ratios and standard errors using the formulae given in Chapter 7 (Section 7.7.6).