When I run a linear regression and include a variable in the regression with as.factor i.e. lm(y ~x +as.factor(x1) and i read the output as as.factor(x1)1.... as.factor(x1)2... etc. how do i interpret the estimate for each level? Is this simply to be regarded as a shift in the equation predicted by the intercept and independent variable x? jdr -- Justin Rapp 409 S. 22nd St. Apt. 1 Philadelphia, PA 19146 Cell:(267)252.0297
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probably you want to look at the help page of ?contr.treatment I hope it helps. Best, Dimitris ---- Dimitris Rizopoulos Ph.D. Student Biostatistical Centre School of Public Health Catholic University of Leuven Address: Kapucijnenvoer 35, Leuven, Belgium Tel: +32/(0)16/336899 Fax: +32/(0)16/337015 Web: http://med.kuleuven.be/biostat/ http://www.student.kuleuven.be/~m0390867/dimitris.htm Quoting Justin Rapp <justin.rapp at gmail.com>:> When I run a linear regression and include a variable in the > regression with as.factor i.e. > > lm(y ~x +as.factor(x1) > > and i read the output as > as.factor(x1)1.... > as.factor(x1)2... > etc. > > how do i interpret the estimate for each level? Is this simply to > be > regarded as a shift in the equation predicted by the intercept and > independent variable x? > > jdr > > > -- > Justin Rapp > 409 S. 22nd St. > Apt. 1 > Philadelphia, PA 19146 > Cell:(267)252.0297 > > ______________________________________________ > R-help at stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! > http://www.R-project.org/posting-guide.html > >Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm
Try this: model.matrix(y ~ x + as.factor(x1)) to see the model matrix that is being used. Matrix multiplication of that matrix by the coefficients is the prediction equation. On 6/23/06, Justin Rapp <justin.rapp at gmail.com> wrote:> When I run a linear regression and include a variable in the > regression with as.factor i.e. > > lm(y ~x +as.factor(x1) > > and i read the output as > as.factor(x1)1.... > as.factor(x1)2... > etc. > > how do i interpret the estimate for each level? Is this simply to be > regarded as a shift in the equation predicted by the intercept and > independent variable x? > > jdr > > > -- > Justin Rapp > 409 S. 22nd St. > Apt. 1 > Philadelphia, PA 19146 > Cell:(267)252.0297 > > ______________________________________________ > R-help at stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html >