I would STRONGLY recommend that you talk to your local statistician. Further:
1. R-help is not a statistical consulting forum 2. Remote statistical consulting is very risky due to the inherent difficulty in communicating all essential context of the problem and data. You have been warned! -- Bert On Tue, Jul 17, 2012 at 2:10 AM, natalie.vanzuydam <nvanzuy...@gmail.com>wrote: > Hi, > > I'm hoping that someone will be able to help. I would like to compare how > covariates associate with the risk of a binary outcome during two periods. > Period 1 will be non-exposure to a treatment and period 2 will be exposure > to a treatment. The same individuals will be examined in each group but I > want to be able to compare the association of certain covariates between > the > two groups to see if there is a treatment interaction. I've looked at > case-crossover designs and time series analysis and don't think that they > are suitable. The cohort has longitudinal data so individuals will go onto > treatment at different times and the effect of the treatment needs to be > administered for a while before it has an effect. The reason why I cannot > just go ahead with an exposed vs unexposed design is that most individuals > in the cohort end up on the treatment eventually and the unexposed group is > very small and lacks power for a meaningful comparison. > > Is there anyway to compare the same individuals during different exposure > times and to look at the effect of different covariates under the exposed > and unexposed conditions? > > Thanks for you help, > Natalie > > ----- > Natalie Van Zuydam > > PhD Student > University of Dundee > nvanzuy...@dundee.ac.uk > -- > View this message in context: > http://r.789695.n4.nabble.com/Stats-question-Comparison-of-the-same-individuals-during-two-exposure-times-tp4636732.html > Sent from the R help mailing list archive at Nabble.com. > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > -- Bert Gunter Genentech Nonclinical Biostatistics Internal Contact Info: Phone: 467-7374 Website: http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
