On 8/3/07, Raoul C Reulen <[email protected]> wrote:
> Dear statalisters,
>
> I've got multiple records per person and want to calculate some kind of cumulative exposure index per person. I've got a variable called "exposure" and want to create a new variable called "cum_exposure". Each observation in the cum_exposure variable should give the sum of all previous cells in the exposure column (but per person). So something like this:
>
> Id Exposure list Cum.Exposure
> 1 10 1 10
> 1 14 2 24
> 1 15 3 39
> 2 8 1 8
> 2 10 2 18
> 2 15 3 32
>
First, what I am really missing in your data example is a time
variable so that a defined sort order is possible. I work in the field
of epidemiology, where exposure typically happens to subject at a
certain point in time and cumulative exposure reflects the exposure
experienced by the subject in the past up to a specified point in
time.
Answering you question, I think one of the most efficient ways is to
use -bysort- (or just -by- if your data is already sorted)
bysort id (timevariable): gen cum_exposure = sum(exposure)
Regards
Sebastian
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