Financial disclosures of authors involved in spine research: an underestimated source of bias

BACKGROUND: Reporting financial disclosures has become standard practice in both journal publications and during oral forum at scientific meetings. Despite this, the effect of reporting a financial disclosure of any member of an authorgroup, on the tone of the conclusion of an article has gained little attention. This study was performed to determine what effect reporting a financial disclosure has on the conclusion of an article. METHODS: A literature search for all articles on interspinous devices and cervical disc prostheses, published from January 1st, 2008 until December 1st, 2010 was performed. Financial disclosures were reported, as were funding by commercially active parties. The tone of the conclusions was graded as positive, neutral or negative. RESULTS: The odds ratio (OR) for a positive conclusion in cases where a financial disclosure was reported was 16.5 (95% CI: 4.7–58.1). Effect modification occurs with the presence of funding by a commercially active party. In cases where a financial disclosure was reported and funding was available for the study, the OR was 1.0 (95% CI: 0.08–12.6), whilst the OR was 33.3 (95%CI: 4.2–262.3) if funding was not provided. This discrepancy is mainly due to the large number of articles with a neutral/negative conclusion if the authors failed to report any financial disclosure and were not funded by a commercially active party. CONCLUSIONS: Reporting a financial disclosure is a potential source of bias. Authors with disclosed financial relationships less often publish articles with a neutral/negative conclusion. This source of bias should certainly be taken into account during the critical appraisal of articles, particularly when the quality of the literature is being assessed. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00586-011-2086-x) contains supplementary material, which is available to authorized users.