Thanks David for your reply. You said "a single slope and intercept are estimated for each variable".Actually I can only get one intercept no matter how many
variables exist,but a slope for each variable. Since the regression is done via:lm(CD4 ~ time + gender + income) It seems that the explanatory variable(time) and the two covariants(gender,income) are treated in the same way,but I think explanatory variable and covariant should be treated differently although I don't know how to do it. Also,they are not both numeric,if gender are F(Female) and M(Male),and income are L(Low),M(median),H(High). 2011/6/28 David Winsemius <dwinsem...@comcast.net> > > On Jun 27, 2011, at 10:02 PM, Lao Meng wrote: > > Hi all,I have some questions about the covariants of regression. >> >> My target: To explore the trend of CD4 level through a period of time. >> >> Response variable: CD4 count >> Explanatory variable:time >> >> Also, the demology information is available,such as >> gender,occupation,income >> level... >> >> Q1,Are these variables of demology information called covariant? >> Q2,How can I correct the impact of "covariant" so that I can get the >> "corrected result" of CD4's change through the time period? >> Q3,How to treat the covariants in regression?I've looked up to many papers >> of R on regression,which treat the covariant in the same >> >> way as the Explanatory variable,like following: >> lm(CD4 ~ time + gender + income) >> > > Yes that seems pretty standard practice. It does, of course, force the > relationships to a) be linear and b) means that a single slope and intercept > are estimated for each variable, neither of a} or b} assumptions may be > true. > > >> From above expression of regression,it's obvious that the response >>> variables >>> >> and covariants are treated the same way, >> > > In what sense are you making that claim? True they are both numeric, but > what else are you saying? > > -- > David > > but acturally >> >> they are totally different. >> >> >> >> Thanks for your help. >> >> My best. >> >> [[alternative HTML version deleted]] >> >> ______________________________**________________ >> R-help@r-project.org mailing list >> https://stat.ethz.ch/mailman/**listinfo/r-help<https://stat.ethz.ch/mailman/listinfo/r-help> >> PLEASE do read the posting guide http://www.R-project.org/** >> posting-guide.html <http://www.R-project.org/posting-guide.html> >> and provide commented, minimal, self-contained, reproducible code. >> > > David Winsemius, MD > West Hartford, CT > > [[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.
