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.