Date Published: October 26, 2010
Publisher: Public Library of Science
Author(s): Andreas Lundh, Marija Barbateskovic, Asbjørn Hróbjartsson, Peter C. Gøtzsche
Abstract: Andreas Lundh and colleagues investigated the effect of publication of large industry-supported trials on citations and journal income, through reprint sales, in six general medical journals
Partial Text: Many medical journals require that authors and peer reviewers declare whether they have any conflicts of interest. Such knowledge can be important for readers when assessing the paper and for editors when assessing the peer review comments.
The impact factor for a given year is calculated as the number of citations in that year to papers published in the two previous years, divided by the number of citable papers published in the two previous years . We focused on two time periods, citations in 1998 for randomised clinical trials (RCTs) published in 1996–1997 and citations in 2007 for RCTs published in 2005–2006, and retrieved citation data using Web of Science on the ISI Web of Knowledge .
We identified 1,429 papers indexed as Randomized Controlled Trials in PubMed (see Text S1) and excluded 61 letters, three editorials, five commentaries, and seven papers that were e-published ahead of print, which yielded a total sample size of 1,353 included RCTs (651 from 1996–1997 and 702 from 2005–2006).
We found that the proportion of industry-supported trials varied widely across journals but changed very little for each journal within the studied time period. Industry-supported trials boosted the approximate impact factor we calculated for all six journals—the most for NEJM and the least for BMJ. Only the two European journals disclosed their main sources of income, and the income from selling reprints was hugely different, as it comprised 41% of the total income for Lancet and only 3% for BMJ.