Context: The number of authors per article has increased markedly in recent years. Little is known about the hierarchical order of authorship and its change over time.
Objective: To assess the change in number and profile of authors of original articles published over a 20-year period in BMJ. It was hypothesized that the number of authors increased over this 20-year period and that it was the senior scientists who benefited most.
Design: Comparative descriptive analysis of the number and academic rank of authors who published original articles in BMJ volumes 270 (1975), 280 (1980), 290 (1985), 300 (1990), and 310 (1995).
Main outcome measures: The specific academic rank, order, and number of authors for each original article. Eight categories of authorship were distinguished as follows: 1, professor; 2, department chairperson; 3, consultant; 4, senior registrar; 5, lecturer and/or registrar; 6, medical student; 7, house officer; and 8, miscellaneous.
Results: The number of original articles published per year decreased from 262 (1975) to 125 (1995). The mean number (SD) of authors per article increased steadily from 3.21 (SD, 1.89) (1975) to 4.46 (SD, 2.04) (1995). Most authors belonged to category 3, and its proportion varied from 24.7% (1975) to 22.6% (1995), while category 1 grew from 13.2% to 20.3%. Category 5 authorship dropped from 24.3% (1975) to 15.8% (1995). With regard to first authorship, category 1 more than doubled from 8.0% (1975) to 16.8% (1995) compared with category 5 whose proportion decreased from 34.0% to 24.8%. Most last authors were from category 1, 20.4% (1975), growing to 29.0% (1995).
Conclusion: Over the last 20 years the number of BMJ authors of original articles increased, mainly because of the rise of authorship among professors and department chairpersons.