Background:
Time-to-event outcomes are commonly used in studies to describe the duration of time until a given event (e.g. death, relapse) occurs. The impact of one intervention versus another on time-to-event outcomes is usually described as a hazard ratio (HR). The GRADEpro GDT tool is a software package widely used to develop evidence profiles and 'Summary of findings' (SoF) tables for systematic reviews. It is reliable and accurate for assessing the certainty in the body of evidence. Moreover, it provides an estimation of the absolute effect sizes based on the entered data on event rates in the control arm.

A recent methodological systematic review (Skoetz et al, submitted) showed that absolute effects based on time-to-event outcomes were calculated correctly and presented in an easy to interpret way in only 18% of Cochrane cancer reviews. This work demonstrated the need for training of review authors working with time-to-event data.

Objectives:
As there is currently no written guidance on how to calculate absolute effects based on HR, and how to best present these in the SoF tables, it might be difficult for review authors to do this correctly. Workshop participants will learn how to calculate and present absolute effects based on time-to-event data within the GRADE framework.

Description:
The GRADE approach to calculating absolute effects is to establish a baseline risk (event rate at a particular point in time) in the control arm and then apply the hazard ratio to calculate the event rate in the treatment arm. The challenge arises around the uncertainty of what the event is that the time-to-event outcomes describe, and how the absolute effect size presentations are interpreted. It is important to distinguish between improving event-free survival (people alive/overall survival) and a decreasing number of events (deaths/mortality).
The workshop will shed light on the problems review authors face when they try to calculate absolute effects based on time-to-event data. In the workshop, brief presentations will alternate with small group exercises and discussions. It is aimed in particular at persons who produce systematic reviews or evidence profiles for guidelines using time-to-event outcomes and for editors.

We would like to invite participants to try-out the software GRADEpro GDT (freely available from: https://gradepro.org/) before the workshop. Please remember that the software may not run properly with the internet browser Internet Explorer.