In the studies we included, poor methodological quality was associated with a discrepancy between results and conclusions, and this in turn was associated with optimistic conclusions in non-government sponsored studies. We found no direct association between these findings and industry funding, but this might have been affected by the sizeable number of studies with undeclared sponsors (23%).
Studies partly or completely sponsored by industry, however, were published in more prestigious journals and are probably cited more, although their methodological quality and size were similar. Some of these findings might help to explain the continuation of a near global policy, despite growing doubts as to its scientific basis.
We reasoned that the combined impact factor and citation index would give us a good idea of the circulation and dissemination of the study (that is, the interest its publication generated). Most of our studies (70%) were of poor quality with overoptimistic conclusions—that is, not supported by the data presented. Those sponsored by industry had greater visibility as they were more likely to be published by high impact factor journals and were likely to be given higher prominence by the international scientific and lay media, despite their apparent equivalent methodological quality and size compared with studies with other funders. Although differences in citation index by study funding are sensitive to the inclusion of the large number of studies with undeclared sources of funding, the higher impact factor and citation index are probably a reflection of a higher profile of industry sponsored studies and a more thorough dissemination of their content.
There are two possible mechanisms involved. Firstly, the same studies are cited more than the others, possibly because of the systematic nature of the dissemination of their results by industry. We have personally observed this on three recent occasions in which industry representatives presented abstracts or reprints of industry sponsored influenza vaccine studies to decision makers, their advisors, and local researchers in an effort to influence their decisions. Symposiums, conferences, and other types of publication further enhance the dissemination process. Often the abstracts were expensively bound and translated into the local language, a tangible sign of their importance to industry.
We cannot say for certain why industry sponsored studies are more attractive to more prestigious journals, but such journals are preferentially targeted by all studies because of their prominence and prestige, so industry sponsored studies might have a higher probability of acceptance. The two mechanisms might be linked, but further research, especially in other specialties, is required. As a measure of transparency for readers and authors, however, we recommend that once a year editors and publishers should post all sources of income related to the running of the journal.
Our finding of lack of concordance between results and conclusions is similar to those of Yank and colleagues in an industry sponsored meta-analysis of antihypertensive drugs.11
In our studies, however, we found a lack of concordance between results and conclusions associated with poor quality rather than any specific sponsorship. Given our findings of lack of concordance in primary studies, the content of current policy might reflect the gap between results and conclusions—that is, synthesis of evidence for policy making might be carried out at two independent levels: that of results and that of conclusions. In most cases, what you see is not necessarily what you get.
What is already known on this topic
- Study sponsorship is associated with optimistic results
- Influenza vaccination continues to be recommended globally, despite growing doubts about the validity of the scientific evidence underpinning policy recommendations
What this study adds
- Evidence is of poor quality, and studies with conclusions in favour of vaccines are of significantly lower methodological quality
- Influenza vaccines studies sponsored by industry are published in journals with higher impact factors and are cited more but are of similar size and quality to the others