IDEAS home Printed from
   My bibliography  Save this paper

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


  • 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)


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

Suggested Citation

  • Sarah Barry & Scott Zeger & Ola Selnes & Maura Grega & Louis Borowicz, Jr. & Guy McKhann, 2004. "Quantitative Methods for Tracking Cognitive Change 3 Years After Coronary Artery Bypass Surgery," Johns Hopkins University Dept. of Biostatistics Working Paper Series 1045, Berkeley Electronic Press.
  • Handle: RePEc:bep:jhubio:1045

    Download full text from publisher

    File URL:
    Download Restriction: no

    More about this item


    Access and download statistics


    All material on this site has been provided by the respective publishers and authors. You can help correct errors and omissions. When requesting a correction, please mention this item's handle: RePEc:bep:jhubio:1045. See general information about how to correct material in RePEc.

    For technical questions regarding this item, or to correct its authors, title, abstract, bibliographic or download information, contact: (Christopher F. Baum). General contact details of provider: .

    If you have authored this item and are not yet registered with RePEc, we encourage you to do it here. This allows to link your profile to this item. It also allows you to accept potential citations to this item that we are uncertain about.

    We have no references for this item. You can help adding them by using this form .

    If you know of missing items citing this one, you can help us creating those links by adding the relevant references in the same way as above, for each refering item. If you are a registered author of this item, you may also want to check the "citations" tab in your RePEc Author Service profile, as there may be some citations waiting for confirmation.

    Please note that corrections may take a couple of weeks to filter through the various RePEc services.

    IDEAS is a RePEc service hosted by the Research Division of the Federal Reserve Bank of St. Louis . RePEc uses bibliographic data supplied by the respective publishers.