I got the code for how to do regression without an intercept out of the back
of my book and the next part of the homework asks me to do it with an
intercept. The problem is, Q1 disappears whenever I try. Here is my code:
Without the intercept:
load("tsa3.rda")>
> Q=factor(rep(1:4,21))
> reg=lm(log(jj)~0+trend+Q,na.action=NULL)
> model.matrix(reg)
trend Q1 Q2 Q3 Q4
1 -10.00 1 0 0 0
2 -9.75 0 1 0 0
3 -9.50 0 0 1 0
4 -9.25 0 0 0 1
5 -9.00 1 0 0 0
...
now, I'm supposed to add an intercept to the regression model. I've hit
a
bit of a problem.
>reg=lm(log(jj)~trend+Q,na.action=NULL)
> model.matrix(reg)
(Intercept) trend Q2 Q3 Q4
1 1 -10.00 0 0 0
2 1 -9.75 1 0 0
3 1 -9.50 0 1 0
4 1 -9.25 0 0 1
5 1 -9.00 0 0 0
Can you help me get Q1 back? thanks.
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On Jan 25, 2012, at 5:24 PM, Rampagegrl wrote:> I got the code for how to do regression without an intercept out of > the back > of my book and the next part of the homework asks me to do it with an > intercept. The problem is, Q1 disappears whenever I try. Here is > my code: > > Without the intercept: > > load("tsa3.rda") >> >> Q=factor(rep(1:4,21)) >> reg=lm(log(jj)~0+trend+Q,na.action=NULL) >> model.matrix(reg) > trend Q1 Q2 Q3 Q4 > 1 -10.00 1 0 0 0 > 2 -9.75 0 1 0 0 > 3 -9.50 0 0 1 0 > 4 -9.25 0 0 0 1 > 5 -9.00 1 0 0 0 > ... > > now, I'm supposed to add an intercept to the regression model. I've > hit a > bit of a problem. > >> reg=lm(log(jj)~trend+Q,na.action=NULL) >> model.matrix(reg) > (Intercept) trend Q2 Q3 Q4 > 1 1 -10.00 0 0 0 > 2 1 -9.75 1 0 0 > 3 1 -9.50 0 1 0 > 4 1 -9.25 0 0 1 > 5 1 -9.00 0 0 0 > > Can you help me get Q1 back? thanks.No. You need to figure out why your instructor assigned you this Zen- like task and why the answer is as I stated. And this is not a homework help line. -- David Winsemius, MD West Hartford, CT
Since this is a homework exercise, I'm guessing that the intent of the problem is for you to figure out why that is happening. albyn On 1/25/12 2:24 PM, Rampagegrl wrote:> I got the code for how to do regression without an intercept out of > the back > of my book and the next part of the homework asks me to do it with an > intercept. The problem is, Q1 disappears whenever I try. Here is my > code: > > Without the intercept: > > load("tsa3.rda") >> >> Q=factor(rep(1:4,21)) >> reg=lm(log(jj)~0+trend+Q,na.action=NULL) >> model.matrix(reg) > trend Q1 Q2 Q3 Q4 > 1 -10.00 1 0 0 0 > 2 -9.75 0 1 0 0 > 3 -9.50 0 0 1 0 > 4 -9.25 0 0 0 1 > 5 -9.00 1 0 0 0 > ... > > now, I'm supposed to add an intercept to the regression model. I've > hit a > bit of a problem. > >>reg=lm(log(jj)~trend+Q,na.action=NULL) >> model.matrix(reg) > (Intercept) trend Q2 Q3 Q4 > 1 1 -10.00 0 0 0 > 2 1 -9.75 1 0 0 > 3 1 -9.50 0 1 0 > 4 1 -9.25 0 0 1 > 5 1 -9.00 0 0 0 > > Can you help me get Q1 back? thanks. > > -- > View this message in context: > > http://r.789695.n4.nabble.com/having-a-bit-of-regression-trouble-tp4328837p4328837.html > Sent from the R help mailing list archive at Nabble.com. > > ______________________________________________ > R-help at 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.