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st: time varying exposures


From   Alison Reid <alisonr@dph.uwa.edu.au>
To   statalist@hsphsun2.harvard.edu
Subject   st: time varying exposures
Date   Fri, 12 Jul 2002 16:41:45 +0800

Hi

I'm hoping that someone reading this list might have a solution to something that I'm having trouble finding an answer to.

What I have is a dataset of asbestos mine workers. I'm keen to explore the impact of time since first exposure (date they started at the mine) on various cancer incidences. This is my time varying exposure as it increases every year that passes. I also have date of birth and date of entry to study. What I have been attempting to do is stsplit to create bands of current age (5 year agebands), then stsplit on the date they started at the mine to get lots of records for time since first exposed (ie a new record for every year that has passed). Then I thought I could create a nested case control study (matching on ageband) and time in study(automatically) and then include the time since first exposed in a conditional logistic regression model. However, the stsplits seem to be working ok, but when it comes to the nested case control - I don't seem to be picking up many/any controls. One suggestion was that all my cases could be falling towards the end of the follow up period, but I've explored this and this isn't the case. My thought is that my time periods are too narrow or too specific (ie 16.23954 years etc ), but I'm not sure how to get around this.

Below are the commands I've been using. I'd be really grateful for any suggestions/assistance or alternatives for how I might deal with this problem.

keep recordno censorcallaero allaeroca smokeq79 birthdate startdat smokex_n evsmoke_n lastalive lastdate datedeat
stset censorcallaero, id(recordno) failure(allaeroca) enter(smokeq79) origin(time smokeq79) scale(365.25)
stsplit ageband, at(20(5)max) after(time=birthdate)
stsplit fstexpband, at(0(1)max) after(time=startdat)
sttocc, match(ageband) n(5)

Thanks

Alison


Alison Reid
Occupational & Environmental Epidemiology Group
School of Population Health
University of Western Australia
35 Stirling Highway, Crawley WA 6009



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