HOW IMPORTANT IS PUBLICATION BIAS - A SYNTHESIS OF AVAILABLE DATA

It has long been recognized that investigators frequently fail to repo rt their research findings (Dickersin, 1990). Chalmers (1990) has sugg ested that this failure represents scientific misconduct since volunte ers who consent to participate in research, and agencies that provide funding support for investigations, do so with the understanding that the work will make a contribution to knowledge. Clearly, knowledge tha t is not disseminated is not making a ''contribution.'' This failure t o publish is not only inappropriate scientific conduct, it also influe nces the information available for interpretation by the scientific co mmunity. Of course, if research is left randomly unpublished, there is less information available, but that information is unbiased. We now have solid evidence that failure to publish is nota random event; rath er, publication is dramatically influenced by the direction and streng th of research findings (Dickersin et al., 1987, 1992; Dickersin & Min , 1993; Easterbrook et al., 1991; Simes, 1986). This tendency of edito rs and reviewers to accept manuscripts submitted by investigators base d on the strength and direction of the research findings is termed ''p ublication bias.'' The problem has been under discussion for many year s and has recently been studied directly in medicine and public health . This article will review the major evidence available regarding publ ication bias and will suggest measures for overcoming the problem.