Quantitative Methods for Tracking Cognitive Change 3 Years After Coronary Artery Bypass Surgery

Sarah Barry, Scott Zeger, Ola Selnes, Maura Grega, Louis Borowicz, Jr. and Guy McKhann
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Sarah Barry: Department of Biostatistics, Johns Hopkins Bloomberg School of Public Health
Scott Zeger: Department of Biostatistics, Johns Hopkins Bloomberg School of Public Health
Ola Selnes: Department of Neurology, The Johns Hopkins School of Medicine
Maura Grega: Division of Cardiac Surgery, The Johns Hopkins School of Medicine
Louis Borowicz, Jr.: The Zanvyl Krieger Mind Brain Institute, The Johns Hopkins University
Guy McKhann: Departments of Neurology & Neuroscience, The Johns Hopkins University School of Medicine and the Zanvyl Krieger Mind Brain Institute, The Johns Hopkins University

No 1045, Johns Hopkins University Dept. of Biostatistics Working Paper Series from Berkeley Electronic Press

Abstract: Background: The analysis and interpretation of change in cognitive function test scores after Coronary Artery Bypass Grafting (CABG). Longitudinal studies with multiple outcomes present considerable statistical challenges. Application of hierarchical linear statistical models can estimate the effects of a surgical intervention on the time course of multiple biomarkers. Methods: We use an "analyze then summarize" approach whereby we estimate the intervention effects separately for each cognitive test and then pool them, taking appropriate account of their statistical correlations. The model accounts for dropouts at follow-up, the chance of which may be related to past cognitive score, by implicitly imputing the missing data from individuals' past scores and group patterns.We apply this approach to a study of the effects of CABG on the time course of cognitive function as measured by 16 separate neuropsychological test scores, clustered into 8 cognitive domains. The study includes measurements on 140 CABG patients and 92 nonsurgical controls at baseline, and 3, 12, and 36 months. Including a nonsurgical control group allows comparison of changes in cognition over time between the surgery group and patients with similar risk factors, controlling for potential effects of aging and vascular disease.Results: We find that CABG patients have very longitudinal changes from baseline in cognitive function similar to those observed for nonsurgical controls. Any small differences tend to favor greater improvement in CABG patients than in the nonsurgical controls. Conclusions: The methods used have application to a wide range of intervention studies in which multiple biomarkers are followed over time to quantify health effects. Software to implement the methods in commonly used statistical packages is available from the authors at http://www.biostat.jhsph.edu/research/software.shtml.

Date: 2004-07-11
Note: oai:bepress.com:jhubiostat-1045
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