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ISSN: 2155-6180

Journal of Biometrics & Biostatistics
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Research Article

Effect of Demographic Risk Factors on the Change in Cognitive Function in the Presence of Non-Participation and Truncation due to Death

Kumar B. Rajan1*, Sue E. Leurgans2, Jennifer Weuve1, Todd L. Beck1 and Denis A. Evans1
1Rush Institute for Healthy Aging, Department of Internal Medicine, Chicago
2Rush Alzheimer’s Disease Center, Department of Neurology & Preventive Med
Corresponding Author : Kumar B. Rajan
Rush Institute for Healthy Aging
Department of Internal Medicine
Chicago, 1645 W Jackson Blvd.
Suite 675, Chicago IL 60612, USA
Tel: (312) 942-3279
Fax: (312) 942-2861
E-mail: kumar_ [email protected]
Received September 08, 2011; Accepted November 16, 2011; Published November 18, 2011
Citation: Rajan KB, Leurgans SE, Weuve J, Beck TL, Evans DA (2011) Effect of Demographic Risk Factors on the Change in Cognitive Function in the Presence of Non-Participation and Truncation due to Death. J Biomet Biostat S3:001. doi:10.4172/2155-6180.S3-001
Copyright: © 2011 Rajan KB, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Abstract

Missing data due to non-participation and death are two common problems in longitudinal studies of the elderly. The effect of socio-demographic variables on the decline in cognitive function after adjusting for non-participation and truncation due to death has not been well studied. This study is based on 6,105 subjects enrolled in the Chicago Health and Aging Project (CHAP), followed over four cycles of data collection approximately three years apart. Cognitive function was based on a standardized measure of mini-mental state examination. We will study the impact of nonparticipation and death on the decline in cognitive function with socio-demographic variables as risk factors, using four different modeling approaches: 1) a linear mixed effects model ignoring the missing data, 2) a pattern-mixture model
using multiple imputation (MI) stratified by patterns of non-participation and death, 3) MI for non-participation stratified by patterns of non-participation and a pattern-mixture model stratified by the time of death, and 4) MI for non-participation stratified by patterns of non-participation and a pattern-mixture model with a categorical variable for time of death. The baseline association of socio-demographic variables with cognitive function was mostly unchanged among Blacks and Whites. However, the decline in cognitive function over a 10-year period had decreased by approximately 50% (Blacks coefficient changed from -0.544 to -0.285; Whites coefficient changed from -0.682 to -0.339) after accounting for nonparticipation and death. The effect of age on the change in cognitive function over a 10-year period had reduced by about 30% (Blacks coefficient changed from -0.033 to -0.010; Whites coefficient changed from -0.049 to -0.016). The trajectory of cognitive function for White males had reduced by approximately 45% (changed from 0.12 to 0.055) over a 10-year period. Education was significantly associated with the change in cognitive function among Blacks but not among Whites. Moreover, females showed a significant change in cognitive function among Whites, but not among
Blacks. We found significant differences on the change in cognitive function between models that did not adjust for nonparticipation and death, and models that adjusted for them.

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