Our study revealed that reporting of conflicts of interest in guidelines of healthcare interventions is probably largely neglected despite some recent improvement. Even in 1999, only 1 out of 6 clinical guidelines disclosed conflicts of interest. Reporting varied by journal. A recent study has shown that 50% of US medical journals with a circulation more than 1000 copies per issue (including, of course, all journals we searched in our study) have written policies regarding conflicts of interest [3
]. Conflicts of interest may not be reported either because authors do not disclose them or because they are not published by the journals. Furthermore, cases of inconsistency between stated journal policy and practice have appeared in the recent literature [5
It is estimated that the pharmaceutical industry in the United States spends $8000 to $13000 per year on each physician simply for marketing purposes [6
] and this phenomenon is probably international [8
]. It is unknown how these figures should be extrapolated to field experts who are authors of clinical guidelines. More studies are needed to examine the extent of financial and other connections of experts to the industry in their field of expertise. One study [9
] found that 15% of lead authors from Massachusetts publishing in 14 major biomedical journals in 1992 had at least one major potential conflict of interest, such as serving on scientific advisory boards of biotechnology firms in their state; being officers, directors or major shareholders in biotechnology firms; or being listed as inventors in a relevant patent or patent application. In all, 34% of the sampled articles had at least one author with a financial conflict of interest directly relevant to the publication [9
]. The proportion might have been larger if financial interest data could have been retrieved from additional out-of-state and international connections and if more non-financial conflicts of interest could have been captured as well. In another study of authors of 70 studies of calcium channel blockers for treating cardiovascular disorders [10
], 96% of the authors of supportive studies had financial relationships with the manufacturers, as compared with 60% of neutral authors and 37% of critical authors. Only 2 of the 70 articles disclosed the authors' potential conflicts of interest. Finally, one study of faculty members at the University of California [11
] found that 7.6% of investigators reported personal financial ties with sponsors of their research. Given the large heterogeneity in the policies of reporting faculty conflicts of interest [12
], it is difficult to arrive at exact estimates of the frequency of serious competing interests in field experts.
In this study, it was not possible to determine exactly what might have been undisclosed, since the authors were sampled from all over the world and guidelines covered very diverse topics. Sorting out financial connections in a consistent fashion would have been practically impossible. Non-financial conflicts of interest would be even more intangible to the outsider. Nevertheless, one may speculate that competing interests may have been at least as common as what has been described in the other studies mentioned above. For example, the 1999 BMJ guideline about the management of hypertension [14
] did not declare any competing interests. In a MEDLINE search, we were able to identify at least 66 randomized controlled trials of anti-hypertensive interventions authored by the guideline authors up to 1999 (range 1 to 34 per author). These trials evaluated a total of 27 different anti-hypertensive drugs (range 0 to 14 per author) in various doses and formulations and 9 other non-pharmaceutical interventions. In any case, funding of trials by the pharmaceutical industry does not mean that the investigators would be biased and it is expected that a panel of leading scientists would be able to balance on objective conclusions during the development of consensus. Still, it would have been useful to know what might have been the potential competing interests, including non-financial ones [15
], of the panel members.
We found that conflicts of interest were rarely, if ever, published in clinical guideline reports funded by the government, universities or professional physician organizations. Although it may be anticipated that such sponsors may make more stringent efforts to assure objectivity in guideline development, it is still important that potential conflicts of interest of the individuals participating in the process should be acknowledged. This holds true even if group authorship is assumed. Conflicts of interest may be more worrisome when there is individual authorship. One would expect the objectivity of the guideline to be more vulnerable when only one or two individuals are authoring it. Nevertheless, the likelihood of disclosing conflicts of interest was smaller when few authors took responsibility for a guideline than when several authors were involved.
Recent studies have focused on deficiencies in the development and reporting of guidelines and have stressed the need to standardize the process [16
]. Conflicts of interest can harm the credibility of guidelines. Competing interests may negatively influence the quality of clinical practice [19
], as well as prescribing and professional behavior [6
]. Even original studies [10
] and cost-effectiveness analyses [20
] may reach differing results depending on competing interests. Clinical guidelines are likely to be even more vulnerable to these influences.