The write position

Publications in peer-reviewed journals are a major criterion for assessing scientists for promotion, tenure or funding (Beasley & Wright, 2003; Thomas et al, 2004). Yet, there are different ways of becoming an author on a scientific publication, and not all authors are viewed as equal contributors. Qualitatively speaking, those listed first or last in the byline are generally apportioned more credit for the work than middle authors. However, exactly how much authors are perceived to contribute from their byline position is not known. Given the central role of publications in evaluating scientific productivity and the trend towards more authors per published paper (Fig 1), it is important that we gain a better quantitative understanding of these perceptions. It is often not possible to objectively determine exactly how much credit each author on a paper deserves for the sum total of the work performed (Laurance, 2006; Tscharntke et al, 2007). Presumably, a larger number of authors dilutes the relative credit awarded to each contributor; however, this effect has not been scientifically confirmed or quantified. Yet, the number of authors per paper in PubMed is growing—so-called ’author inflation’. This is an increasing trend in many research fields largely owing to the increasing pressure to publish, specialization of research expertise, collaborative efforts and honorary authorships, also known as ‘gift authorships’ (Drenth, 1998; Lazar, 2004; Mussurakis, 1993; Kwok, 2005; Mowatt et al, 2002; Smith, 1994; Tarnow, 2004a). Although the International Committee of Medical Journal Editors (ICMJE; Washington, DC, USA) has formally defined authorship criteria, many researchers define authorship differently (ICMJE, 2006; Eastwood et al, 1996; Tarnow, 1999). Without explicit statements about each author’s contributions to the work described, readers—including promotion committee members—implicitly apportion authorship credit and frequently do so in the absence of any well-defined standards (Tarnow, 2004b). Most biomedical authors are aware, in an informal sense, that the first and last author positions are generally perceived as the ‘key’ positions on a paper; but there is no consensus on the value of other positions. Surveys of first authors have shown that their perceptions of their co-author(s)’s contributions can vary greatly between the papers they publish (Shapiro et al, 1994). The differing values of byline positions become evident in the case of ‘joint first authors’ or declarations that authors ‘contributed equally’. Presumably, in the absence of such a statement, readers might assume that the contribution of the second author is less than it actually was. Quantitatively, the relative importance of different byline positions is not known, nor the effect of adding new authors. In the absence of explicit information, editors and committee members often make decisions based on assumptions. Editors, for example, seeking reviewers for a paper, will search the literature for authors publishing similar papers and invite them as a reviewer on the basis of their perceived expertise. Yet, the literature often does not contain any more 40%