Clinical research in general medical journals: a 30-year perspective.

Little is known about the frequency with which various research designs appear in the clinical literature and how this frequency has changed in recent years. This study describes the research designs used in 612 articles randomly selected from original research published in three general medical journals from 1946 to 1976. Cross-sectional studies increased from 25 to 44 per cent, cohort studies declined from 59 to 34 per cent, and clinical trials increased from 13 to 21 per cent of articles (P less than 0.001). Randomized controlled trials comprised 5 per cent of articles published in 1976 and were not represented 30 years before. In 1976, 37 per cent of articles reported on 10 subjects or less, and this number has not changed substantially since 1946. The frequency of studies with weak research designs has increased in these general medical journals over the past 30 years. The trend deserves critical attention.