Objective
To investigate the association between conflicts of interest and
favourable recommendations in clinical guidelines, advisory committee
reports, opinion pieces, and narrative reviews.
Design
Systematic review.
Eligibility criteria
Studies that compared the association between conflicts of interest
and favourable recommendations of drugs or devices (eg, recommending a
drug) in clinical guidelines, advisory committee reports, opinion pieces
(eg, editorials), or narrative reviews.
Data sources
PubMed, Embase, Cochrane Methodology Register (from inception to
February 2020), reference lists, Web of Science, and grey
literature.
Data extraction and analysis
Two authors independently extracted data and assessed the
methodological quality of the studies. Pooled relative risks and 95%
confidence intervals were estimated using random effects models
(relative risk >1 indicates that documents with conflicts of interest
more often had favourable recommendations than documents with no
conflicts of interest). Financial and non-financial conflicts of
interest were analysed separately, and the four types of documents were
analysed separately (preplanned) and combined (post hoc).
Results
21 studies that analysed 106 clinical guidelines, 1809 advisory
committee reports, 340 opinion pieces, and 497 narrative reviews were
included. Unpublished data were received for 11 studies (eight full
datasets and three summary datasets). 15 studies showed risk of
confounding because the compared documents could differ in factors other
than conflicts of interest (eg, different drugs used for different
populations). The relative risk for associations between financial
conflicts of interest and favourable recommendations for clinical
guidelines was 1.26 (95% confidence interval 0.93 to 1.69; four studies
of 86 clinical guidelines), for advisory committee reports was 1.20
(0.99 to 1.45; four studies of 629 advisory committee reports), for
opinion pieces was 2.62 (0.91 to 7.55; four studies of 284 opinion
pieces), and for narrative reviews was 1.20 (0.97 to 1.49; four studies
of 457 narrative reviews). An analysis of all four types of documents
combined supported these findings (1.26, 1.09 to 1.44). In one study
that investigated specialty interests, the association between including
radiologists as authors of guidelines and recommending routine breast
cancer was: relative risk 2.10, 95% confidence interval 0.92 to 4.77; 12
clinical guidelines).
Conclusions
We interpret our findings to indicate that financial conflicts of
interest are associated with favourable recommendations of drugs and
devices in clinical guidelines, advisory committee reports, opinion
pieces, and narrative reviews. Limitations of this review were risk of
confounding in the included studies and the statistical imprecision of
individual analyses of each document type. It is not certain whether
non-financial conflicts of interest influence recommendations.
Systematic review registration
Cochrane Methodology Review Protocol MR000040.
