Reporting on statistical methods to adjust for confounding:: A cross-sectional survey

Background: The use of complex statistical models to adjust for confounding is common in medical research. Objective: To determine the frequency and adequacy of adjustment for confounding in medical articles. Design: Cross-sectional survey. Setting: 34 scientific medical journals with a high impact factor. Measurements: Frequency of reporting on methods used to adjust for confounding in 537 original research articles published in January 1998. Results: Of the 537 articles, 169 specified that adjustment for confounding was used. In 1 paper in 10, it was unclear which statistical method was used or for which variables adjustment was made. In 45% of papers, it was not clear how multicategory or continuous variables were treated in the analysis. inadequate reporting was less frequent if an author was affiliated with a department of statistics, epidemiology, or public health and if articles were published in journals with a high impact factor. Conclusions: Details of methods used to adjust for confounding are frequently not reported in original research articles.