On Apr 15, 2013, at 8:55 AM, Laura MacCalman wrote: > > HI > > I am trying to analyse data which is left-censored (i.e. has values below the > detection limit). I have been using the NADA package of R to derive summary > statistics and do some regression. I am now trying to carry out regression on > paired data where both my X and Y have left-censored data within them. > > I have tried various commands in R: > > rega = cenreg(Cen(conc, cens_ind) ~ Gp_ident)) > with all X and Y data stacked and using a group identifier to look at the > differences > > this doesn't take account of the paired data though. > > I have also tried splitting the data and regessing one on the other > > rega = cenreg(Cen(conc1, censind1) ~ Cen(conc2,censind2)) > > which doesn't work. > > Does anyone know of a command that will work - or perhaps suggest another > package that I could use? > > I have also looked at multiple imputation packages but they all seem to > impute data depending on other columns - whereas I would want to impute data > between zero and the censored value. > > Any guidance/advice would be very much appreciated.
The `survival::Surv` function allows left censoring and the `coxph` function allows strata or clusters to be specified. My understanding is that for many years analysts used the Cox regression machinery to crank out conditional logistic regression by creating two-member (or 1+n) member strata/cluster. I'm wondering if that could be made to work here, since this seems even closer to a "real" survival analysis problem. This response from Terry Therneau (looked up with Markmail) to a question about a right-censored situation suggests that the use of cluster() rather than strata() might be be more powerful: http://markmail.org/message/c2oqqd34nujxvuvi?q=list:org%2Er-project%2Er-help+paired+survival+coxph+strata -- David. > > Laura > > > > Dr Laura MacCalman Msci MSc PhD Gradstat > Senior Statistician > > Institute of Occupational Medicine > Research Avenue North > Riccarton > Edinburgh > EH14 4AP > > Tel: 0131 449 8078 > Fax: 0131 449 8084 > Mob: 07595 054 881 > Email: laura.maccal...@iom-world.org > > Web: http://www.iom-world.org > > > -------------------------------------------------------------------------- > > The Institute of Occupational Medicine (IOM) is a company limited by > guarantee, registered in Scotland (No.SC123972) and a Registered Scottish > Charity (No.SC000365). IOM Consulting Ltd is a wholly owned subsidiary of IOM > and a private limited company registered in Scotland (No. SC205670). > Registered Office: Research Avenue North, Riccarton, Edinburgh, EH14 4AP, Tel > +44 (0)131 449 8000. > > This email and any files transmitted with it are confide...{{dropped:18}} > > ______________________________________________ > 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. David Winsemius Alameda, CA, USA ______________________________________________ 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.
