In a review of 332 RCTs in both surgery and medicine, the authors' declaration of industry funding was significantly associated with statistically significant pro-industry results. Adjusting for variations in study quality and sample size across studies further strengthened the results. Our results fail to support the belief that variations in study quality or sample size (study power) can explain differences in trial results across industry-funded and non-industry-funded trials.
However, our findings are limited by the quality of reporting of industry funding in the journals publishing these RCTs. We reviewed each journal's “Information to Authors” section to identify policies on conflict of interest and disclosure of funding. Of 8 surgical journals, 6 required disclosure of industry funding and 2 suggested that such disclosure was appropriate. These 2 journals (Journal of Bone and Joint Surgery [British volume] and Acta Orthopaedica Scandinavica) also allowed a no-response category regarding financial disclosure. Of the 5 medical journals, 3 required disclosure of industry funding and the other 2 (JAMA and New England Journal of Medicine) suggested disclosure.
Our study has some limitations, such as our decision to use a composite scale to assess trial quality versus a component-oriented approach. Numerous checklists and scales have been reported for the evaluation of the quality of RCTs,10
and a major disadvantage of the Detsky scale, as with any such scale, is that assessments of quality depend on the information available in the published reports. As well, important aspects of study quality may not be captured by this index, such as the inappropriate use of placebos or inactive controls, or controls that are compromised by insufficient dosage or mode of administration. Composite quality scales, such as the Detsky index, may provide a useful overall assessment when comparing groups of trials, but they have been criticized, and it has been proposed that more rigorous evaluation may result if the relevant methodological aspects were identified, ideally a priori
, and assessed individually.11
Inferences about differences in the results of surgical and medical trials may be limited by sample size. Only 16 (18%) of all 87 identified surgical trials reported industry funding. Although the point estimate of the odds ratios suggests that surgical trials are more likely than medical trials to have pro-industry results, this difference was not statistically significant and larger studies are required to explore this finding.
Our study may be influenced by selection bias, as we elected to search only high-impact journals for trials. As well, our method of determining our primary outcome measure, although strengthened by substantial inter-observer reliability, may be questionable. Some authors2
have made use of a validated scale to grade studies' conclusions regarding the extent to which an experimental intervention was favoured,1
have used an approach similar to ours.
Our findings are contradictory to those of some reports.4,5,6,7
Clifford and colleagues4
did not find that trial outcome was associated with industry funding (p
= 0.46). However, their study may have been limited by type II error and limited disclosure of funding sources. Some previous studies support our results.1,2,3,8
In a recent meta-analysis, Bekelman and colleagues8
pooled 1140 original studies and found a statistically significant association between industry sponsorship and pro-industry conclusions (pooled OR 3.60, 95% CI 2.63–4.91). We pooled these results with those of Clifford and colleagues4
(100 trials) and our own using a random effects model. Pooling was deemed appropriate due to a nonsignificant test of heterogeneity (p
> 0.1), widely overlapping confidence intervals and similarity of point estimates. Our pooled sample of 1572 trials provides a current estimate of the impact of industry funding on authors' conclusions (pooled OR 2.3, 95% CI 1.3–4.1, heterogeneity p
= 0.02) ().
Fig. 1: Comparison of current results with a meta-analysis of 1140 medical trials and a recent study of 100 trials. Point estimates from our current sample of 158 drug trials and 87 nonsurgical, nondrug trials support previous estimates from the meta-analysis. (more ...)
Our findings suggest that industry funding has a significant influence on the results of both surgical trials and drug trials. Perhaps by careful selection, industry funds trials that are most likely to reveal a benefit of the experimental intervention. Results of industry-funded trials may be influenced by inappropriate choice of comparator intervention2
or by publication bias. Future exploration of the complex relation between industry-funded trials and authors' conclusions will shed further light on this issue.
β See related article page 481