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Fujian Song a Department of Public Health and Epidemiology,
University of Birmingham, Birmingham B15 2TT, b Centre for Statistics in
Medicine, Institute of Health Sciences, Oxford OX3 7LF, c Cochrane Oral Health Group, University Dental Hospital of
Manchester, Manchester M15 6FH
Correspondence to: F Song f.song{at}bham.ac.uk
Objective:
To determine the validity of adjusted
indirect comparisons by using data from published meta-analyses of
randomised trials.
What is already known on this topic
Indirect comparison of competing interventions has been carried out in
systematic reviews, often implicitly Indirect comparison adjusted by a common control can partially take
account of prognostic characteristics of patients in different trials What this study adds
The validity of adjusted indirect comparisons depends on the internal
validity and similarity of the trials involved
Design:
Direct comparison of different interventions in randomised trials and adjusted indirect comparison in which two
interventions were compared through their relative effect versus a
common comparator. The discrepancy between the direct and adjusted
indirect comparison was measured by the difference between the two estimates.
Data sources:
Database of abstracts of reviews of
effectiveness (1994-8), the Cochrane database of systematic reviews,
Medline, and references of retrieved articles.
Results:
44 published meta-analyses (from 28 systematic reviews) provided sufficient data. In most cases, results of
adjusted indirect comparisons were not significantly different from
those of direct comparisons. A significant discrepancy (P<0.05) was observed in three of the 44 comparisons between the direct and the
adjusted indirect estimates. There was a moderate agreement between the
statistical conclusions from the direct and adjusted indirect
comparisons (
0.51). The direction of discrepancy between the two
estimates was inconsistent.
Conclusions:
Adjusted indirect comparisons usually
but not always agree with the results of head to head randomised
trials. When there is no or insufficient direct evidence from
randomised trials, the adjusted indirect comparison may provide useful
or supplementary information on the relative efficacy of competing interventions. The validity of the adjusted indirect comparisons depends on the internal validity and similarity of the included trials.
Many competing interventions have not been compared in randomised
trials
Results of adjusted indirect comparison usually, but not always, agree
with those of head to head randomised trials
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