I think it is zero, because you have lots of zeros there. It is not like continous variables.
Thomas Lumley wrote: > > On Wed, 2 Jul 2008, rlearner309 wrote: > >> >> I think the covariance between dummy variables or between dummy variables >> and >> intercept should always be zero. meaning: no sigularity problem?? >> > > No. You can easily check that this is not true using the cov() function. > Indicator variables for mutually exclusive groups are negatively > correlated. > > -thomas > > > >> >> rlearner309 wrote: >>> >>> This is actually more like a Statistics problem: >>> I have a dataset with two dummy variables controlling three levels. The >>> problem is, one level does not have many observations compared with >>> other >>> two levels (a couple of data points compared with 1000+ points on other >>> levels). When I run the regression, the result is bad. I have >>> unbalanced >>> SE and VIF. Does this kind of problem also belong to "near sigularity" >>> problem? Does it make any difference if I code the level that lacks >>> data >>> (0,0) in stead of (0,1)? >>> >>> thanks a lot! >>> >> >> -- >> View this message in context: >> http://www.nabble.com/A-regression-problem-using-dummy-variables-tp18214377p18237666.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. >> > > Thomas Lumley Assoc. Professor, Biostatistics > [EMAIL PROTECTED] University of Washington, Seattle > > ______________________________________________ > 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. > > -- View this message in context: http://www.nabble.com/A-regression-problem-using-dummy-variables-tp18214377p18248187.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.
