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st: Estimating Independent Contribution of Each Alzheimer's Risk Factor


From   William Rodman Shankle <rshankle@mccare.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: Estimating Independent Contribution of Each Alzheimer's Risk Factor
Date   Thu, 06 Jul 2006 10:02:47 -0700

Dear Statalisters,
I would appreciate any knowledge whether the following method estimates
the independent effect of each AD risk factor
1.  Data:
   a. 81 studies measured the relative risk ratio of AD (Y, the
dependent variable).
   b. Among these 81 studies, 41 risk factors (X, the independent
variables) were found make significant contribution to AD relative risk.
   c. Each study measured only a subset of the 41 risk factors.
   d. One therefore does not know, from any single study, what are the
independent contributions of each AD risk factor.

2. Method:
   a. Treat the 81 studies as 81 rows of a matrix.  Each row is
characterized by the AD relative risk ratio, Y.
   b. Treat the 41 AD risk factors, X, as the columns of this matrix.
   c. For each study (row),  put a "1" in all columns where the risk
factors were measured, and put a "0" in all columns where the risk
factors were not measured.
   d. This gives an 81 by 41 binary matrix.
   d. Apply matrix algebra, Y = B*X to estimate the independent
coefficients, B, of each AD risk factor
   e. I think this method is equivalent to a multivariate linear
regression model.

Are the estimated coefficients, B, truly independent of each other?
If not, are there any suggestions about making them more independent?

Thank you for your knowledge,
Sincerely,
Rod Shankle

--
William Rodman Shankle, MS MD
Neurologist Specialized in Alzheimer's Disease and Related Disorders
Research Fellow, Cognitive Sciences, UC Irvine
Chief Medical Officer, Medical Care Corporation
Office: 949 833 2383
Facsimile: 949 838 0153
Address: 19782 Macarthur Blvd, Suite 310, Irvine, CA 92612


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