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Multivariable Models in Biobehavioral Research

From the Departments of Psychiatry (K.E.F., B.C.S.) and Psychology (R.L.R.), Washington University School of Medicine, St. Louis, Missouri.

Address correspondence and reprint requests to Kenneth E. Freedland, Department of Psychiatry, Washington University School of Medicine, 4320 Forest Park Ave., Suite 301, St. Louis, Missouri 63108. E-mail: freedlak{at}bmc.wustl.edu

Objective: To review contemporary multivariable modeling and statistical reporting practices in psychosomatic and behavioral medicine research.

Methods: A random sample of 40 original research articles involving multivariable models was obtained from the 2005 volumes of four of the leading psychosomatic and behavioral medicine research journals. A random comparison sample was obtained from the 2005 volumes of four of the leading general medical and psychiatric journals. Multivariable modeling and reporting practices were systematically coded. The evaluation focused primarily on issues raised in 2004 Statistical Corner article by Babyak.

Results: Deficiencies were found in a large proportion of the articles published in psychosomatic and behavioral medicine journals. The single most common problem was a lack of clear information, or any information at all, about important aspects of the statistical methods. Other frequent problems included post hoc selection of variables, lack of clear rationales and well-specified roles for selected variables, inadequate information about models as a whole (e.g., goodness of fit), failure to test model assumptions, and lack of model validation. Overfitting of multivariable models was the exception rather than the rule, but still a significant problem.

Conclusions: There is room for improvement in the use and reporting of multivariable models in psychosomatic and behavioral medicine research journals. These problems can be overcome by adopting best statistical practices, such as those recommended by Psychosomatic Medicine’s statistical guidelines and by authoritative guidebooks on statistical reporting practices.

Key Words: statistical methods • statistical models • analysis of covariance • multiple regression • logistic regression • survival analysis

Abbreviations: AIPE = accuracy in parameter estimation; BDI = Beck Depression Inventory; BMI = body mass index; IV = independent variable; RCT = randomized controlled trial.