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st: Recency Weighted cumulative exposures
From
"Carmine Rossi, Mr" <[email protected]>
To
"[email protected]" <[email protected]>
Subject
st: Recency Weighted cumulative exposures
Date
Wed, 13 Nov 2013 22:08:58 +0000
Dear STATA listers,
I have the following repeated measures data on two subjects with a dose exposure variable. I am interested in creating a variable called “result” that is a recency-weighted cumulative sum.
id time dose result
1 1 0 0
1 2 0 0
1 3 2.6 2.6
1 4 2.6 5.174
1 5 3.2 8.218
2 1 0 0
2 2 0 0
2 3 0.7 0.7
2 4 0.7 1.393
The “result” variable is obtained as a cumulative sum using a weight function:
Summation of (Dose(i) x weight(t)), where the weight function is:
W(t) = exp((-(delta time)2)/70.70)
So to get the weighted cumulative sum value of 8.218 (for subject 1 at time 5), rather than 8.4, which would have been the un-weighted cumulative sum, I did the following in a spreadsheet.
Id time dose delta_t w(t) dose(t)*weight(t) cumulative_sum
1 1 0 4 0.80 0 0
1 2 0 3 0.88 0 0
1 3 2.6 2 0.94 2.444 2.444
1 4 2.6 1 0.99 2.574 5.018
1 5 3.2 0 1 3.2 8.218
Is there a way to do this in STATA with loops? Can anyone provide any suggestions?
Carmine Rossi
PhD Candidate, Epidemiology
McGill University
[email protected]
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