I have expenditures post-stroke at one month intervals and want to predict
these expenditures by number of months post stroke controlling for other
covariates. For this purpose, I am using dummy variables for the number of
months post stroke. For example, if I have 12 months of follow-up I'm using
11 dummies for each month up to 11 months and keeping 12th month as my ref
category. Now, after fitting this OLS I want to take the mean of predicted
values for each month and compare the predicted values across months. When I
do that what I find is that the mean predicted values are the same as the
mean observed values for each month. I just can't conceptualize why they are
the same. When I stratify the predicted values by gender, I again get the
same values as I would if I stratified the observed values by gender.
Can someone help?
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Puneet K Singhal, M.S.
Doctoral Candidate
Pharmaceutical Health Services Research Program
University of Maryland
Baltimore, MD-21201
Phone: 410-706-1805
Fax: 410-706-1488
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