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The influence of study characteristics on reporting of subgroup analyses in randomised controlled trials: systematic review

BMJ 2011; 342 doi: https://doi.org/10.1136/bmj.d1569 (Published 28 March 2011) Cite this as: BMJ 2011;342:d1569

Rapid Response:

The importance of prespecification

The paper by Sun et al [1] is a useful reminder to the medical
profession about the need for caution when interpreting trials with
subgroup analyses, particularly in trials with non-significant primary
outcomes and when the subgroup analyses are not prespecified. However, in
view of the importance of prespecification, it is disappointing to find
that Sun et al's analysis appears to have deviated from their prespecified
analysis plan [2].

In the analysis plan, Sun et al state that they will analyse the
influence of study characteristics (industry funding, study size etc) on
whether reports of trials that included a subgroup analysis make a claim
of a subgroup effect on the basis of that analysis. That analysis does not
appear to be reported.

On the other hand, Sun et al do report an analysis of the factors
associated with prespecification of subgroup analysis, although that
analysis, ironically, does not appear to have been prespecified.

We would be grateful if Sun et al could explain these apparent
discrepancies between the results that they report and their prospectively
published analysis plan.

References:

1. Sun X et al. The influence of study characteristics on reporting
of subgroup analyses in randomised controlled trials: systematic review
BMJ 2011; 342:d1569

2. Sun X et al. Subgroup Analysis of Trials Is Rarely Easy (SATIRE):
a study protocol for a systematic review to characterize the analysis,
reporting, and claim of subgroup effects in randomized trials. Trials
2009;10:101

Competing interests: AJ & SH are the director and an employee of Dianthus Medical Limited, a company which provides professional medical writing services to both industry-funded and non-industry-funded researchers, but much more often to the former.

18 April 2011
Adam Jacobs
Director
Sam Hampson
Dianthus Medical Limited