Abstract
It is essential to choose a realistic
anticipated intervention effect when calculating a
sample size for a randomised clinical trial. Unfortunately,
anticipated intervention effects are often inflated, when
compared with the ‘true’ intervention effects. This is
documented for mortality in critical care trials. A similar
pattern might exist across different medical specialties.
This study aims to estimate the range of observed
intervention effects for all-cause
mortality in trials included
in Cochrane Reviews, within each Cochrane Review Group.
Methods and analysis We will include randomised
clinical trials assessing all-cause
mortality as an outcome.
Trials will be identified from Cochrane Reviews published
in the Cochrane Database of Systematic Reviews.
Cochrane Reviews will be clustered according to the
registered Cochrane Review Group (eg, Anaesthesia,
Emergency and Critical Care) and the statistical analyses
will be conducted for each Cochrane Review Group and
overall. The median relative risk and IQR for all-cause
mortality and the proportion of trials with a relative all-cause
mortality risk within seven different ranges will be
reported (relative risk below 0.70, 0.70–0.79, 0.80–0.89,
0.90–1.09, 1.10–1.19, 1.20–1.30 and above 1.30).
Subgroup analyses will explore the effects of original
design, sample size, risk of bias, disease, intervention
type, follow-up
length, participating centres, funding type,
information size and outcome hierarchy.
Ethics and dissemination Since we will use summary
data from trials already approved by relevant ethical
committees, this study does not require ethical approval.
Regardless of our findings, the results will be published in
an international peer-reviewed
journal.