Reporting on Statistical Methods To Adjust for Confounding: A Cross-Sectional Survey

Reporting on Statistical Methods To Adjust for Confounding: A Cross-Sectional Survey

Marcus Müllner, MD;
Hugh Matthews, BSc, MBBS; and
Douglas G. Altman, DSc

From BMJ London, and ICRF Medical Statistics Group, Oxford, United Kingdom.

Abstract

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.

Article and Author Information

Acknowledgments: The authors thank the BMJ staff, particularly Richard Smith, for providing the environment that enabled this research project.
Requests for Single Reprints: Marcus Müllner, MD, Universitätsklinik für Notfallmedizin, Allgemeines Krankenhaus Wien, Währinger Gürtel 18-20/6D, A-1090 Vienna, Austria; e-mail, marcus.muellner{at}univie.ac.at.
Current Author Addresses: Dr. Müllner: Universitätsklinik für Notfallmedizin, Allgemeines Krankenhaus Wien, Währinger Gürtel 18-20/6D, A-1090 Vienna, Austria.
Mr. Matthews: Sandbanks, Graveney, Faversham, Kent ME13 9DJ, United Kingdom.
Dr. Altman: ICRF Medical Statistics Group, Centre for Statistics in Medicine, Institute of Health Sciences, Old Road, Headington, Oxford OX3 7LF, United Kingdom.
Author Contributions: Conception and design: M. Müllner, H. Matthews, D.G. Altman.
Analysis and interpretation of the data: M. Müllner, D.G. Altman.
Drafting of the article: M. Müllner, H. Matthews, D.G. Altman.
Critical revision of the article for important intellectual content: M. Müllner, H. Matthews, D.G. Altman.
Final approval of the article: M. Müllner, H. Matthews, D.G. Altman.
Statistical expertise: M. Müllner, D.G. Altman.
Administrative, technical, or logistic support: M. Müllner.
Collection and assembly of data: M. Müllner, H. Matthews.