Format

Send to:

Choose Destination
See comment in PubMed Commons below
BMJ. 2008 Mar 15;336(7644):601-5. doi: 10.1136/bmj.39465.451748.AD. Epub 2008 Mar 3.

Empirical evidence of bias in treatment effect estimates in controlled trials with different interventions and outcomes: meta-epidemiological study.

Author information

  • 1Department of Social Medicine, University of Bristol, Bristol BS8 2PR.

Abstract

OBJECTIVE:

To examine whether the association of inadequate or unclear allocation concealment and lack of blinding with biased estimates of intervention effects varies with the nature of the intervention or outcome.

DESIGN:

Combined analysis of data from three meta-epidemiological studies based on collections of meta-analyses.

DATA SOURCES:

146 meta-analyses including 1346 trials examining a wide range of interventions and outcomes.

MAIN OUTCOME MEASURES:

Ratios of odds ratios quantifying the degree of bias associated with inadequate or unclear allocation concealment, and lack of blinding, for trials with different types of intervention and outcome. A ratio of odds ratios <1 implies that inadequately concealed or non-blinded trials exaggerate intervention effect estimates.

RESULTS:

In trials with subjective outcomes effect estimates were exaggerated when there was inadequate or unclear allocation concealment (ratio of odds ratios 0.69 (95% CI 0.59 to 0.82)) or lack of blinding (0.75 (0.61 to 0.93)). In contrast, there was little evidence of bias in trials with objective outcomes: ratios of odds ratios 0.91 (0.80 to 1.03) for inadequate or unclear allocation concealment and 1.01 (0.92 to 1.10) for lack of blinding. There was little evidence for a difference between trials of drug and non-drug interventions. Except for trials with all cause mortality as the outcome, the magnitude of bias varied between meta-analyses.

CONCLUSIONS:

The average bias associated with defects in the conduct of randomised trials varies with the type of outcome. Systematic reviewers should routinely assess the risk of bias in the results of trials, and should report meta-analyses restricted to trials at low risk of bias either as the primary analysis or in conjunction with less restrictive analyses.

PMID:
18316340
[PubMed - indexed for MEDLINE]
PMCID:
PMC2267990
Free PMC Article
PubMed Commons home

PubMed Commons

0 comments
How to join PubMed Commons

    Supplemental Content

    Full text links

    Icon for HighWire Icon for PubMed Central
    Loading ...
    Write to the Help Desk