The key guide to estimating hazard ratios from published data gets a major update

23 Apr 2025

Meta-analysis researchers at the MRC Clinical Trials Unit at UCL have released a new guide to methods for estimating hazard ratios from published time-to-event analyses. The previous version of the guidance, published in 2007, was crowned Trials Journal’s most cited paper of all time at the journal’s 10th anniversary, and has amassed more than 5,000 citations as of March 2025. 

In clinical trials, hazard ratios are a way of describing the effect of a treatment on time-to-event outcomes, such as the time taken for the disease to worsen or for symptoms to resolve. They are calculated by comparing the rate at which the event occurs over time between two groups of participants. 

Ideally, researchers conducting a meta-analysis of time-to-event outcomes would be able to extract a hazard ratio and a measure of the associated variance directly from a published trial report to use in meta-analysis. However, if trial reports do not provide such statistics, researchers must estimate them from other published statistics or from data extracted from Kaplan-Meier curves.  

Recognising that this was challenging for researchers with limited statistical training, the team at the MRC CTU at UCL created the previous guide to explain the methods in simpler terms and provided a spreadsheet to facilitate the calculations.  

Since its publication, the guide has become widely used worldwide. But gaps and common misconceptions about the methodology remain. 

Therefore, the team have created a comprehensively updated version of the guide, now published in Systematic Reviews. This clarifies ambiguities and explores additional scenarios to help meta-analysts better understand how and when to apply the methods. It also incorporates alternative methodologies that have emerged since the original paper’s publication. 

An accompanying spreadsheet, with an enhanced user interface, will perform all the necessary calculations based on the data entered.  

This update offers considerable assistance to researchers producing meta-analyses of published, time-to-event outcomes.

Further information: 

• Practical methods for incorporating summary time-to-event data into meta-analysis: updated guidance 
• Practical methods for incorporating summary time-to-event data into meta-analysis (original guidance)
• The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate healthcare interventions: explanation and elaboration