[R] [NB] lm problems
Matej Cepl
matej at ceplovi.cz
Wed Nov 27 02:04:04 CET 2002
Well, I do think it IS silly idea (moreover, in one other case we
do regression analysis where dependent variable is sex -- which
seems to me really ugly), but it is my homework assignment from
statistics class. Not to make my instructor too silly, they have
the problem that an example dataset for the textbook has just one
interval variable. On the other hand instructor (James Fox, your
namesake BTW -- School of Criminal Justice at Northeastern
University, Boston, MA) is the author of the textbook so I think,
that there should be really TWO datasets (one for tests of
significance and variance and other one for regression
calculations) and that it is his fault after all.
Thanks for the help,
Matej
On Tue, 26 Nov 2002, John Fox wrote:
> Dear Matej,
>
> The response variable in a linear model fit by lm has to be a numeric
> variable. (The warnings are produced when lm tries to perform arithmetic
> operations on an ordered factor.) You could use as.numeric(G5) on the left
> hand side of the model, but you should probably think about whether you
> really want to fit a linear model to categorical data.
>
> I hope that this helps,
> John
>
> At 03:40 PM 11/26/2002 -0500, Matej Cepl wrote:
> >Hi,
> >
> >I have probably overlooked something obvious, but could anybody
> >help me with following, please?
> >
> >Trying to make regression analysis. I have a huge dataframe with
> >results from National Opinion Survey on Crime and Justice
> >(www.abacon.com/fox/) with two variables G5 and N3 which are
> >imported to R as ordered factors:
> >
> > > levels(noscj$G5)
> > [1] "Strongly agree" "Agree" "Neither"
> > [4] "Disagree" "Strongly disagree"
> > > levels(noscj$N3)
> > [1] "Serious problem" "Somewhat problem" "Minor problem" "Not
> > a problem"
> > >
> >
> >(missing values are duly recoded as NA). When I try linear
> >regression I get a lot of warnings which I have not managed to
> >parse succesfully:
> >
> > > lm(G5 ~ N3,data=noscj)
> >
> > Call:
> > lm(formula = G5 ~ N3, data = noscj)
> >
> > Coefficients:
> > (Intercept) N3.L N3.Q N3.C
> > 3.38087 -0.05821 -0.15364 0.04367
> >
> > Warning message:
> > "-" not meaningful for ordered factors in: Ops.ordered(y,
> > z$residuals)
> > > summary(lm(G5 ~ N3,data=noscj))
> >
> > Call:
> > lm(formula = G5 ~ N3, data = noscj)
> >
> > Residuals:
> > [1] <NA> <NA> <NA> <NA> <NA>
> > Levels: Strongly agree Agree Neither Disagree Strongly disagree
> >
> > Coefficients:
> > Estimate Std. Error t value Pr(>|t|)
> > (Intercept) 3.38087
> > N3.L -0.05821
> > N3.Q -0.15364
> > N3.C 0.04367
> >
> > Residual standard error: NA on 980 degrees of freedom
> > Multiple R-Squared: NA, Adjusted R-squared: NA
> > F-statistic: NA on 3 and 980 DF, p-value: NA
> >
> > Warning messages:
> > 1: "-" not meaningful for ordered factors in: Ops.ordered(y,
> > z$residuals)
> > 2: "^" not meaningful for ordered factors in: Ops.ordered(r, 2)
> > 3: ">" not meaningful for factors in: Ops.factor(qs[i], -Inf)
> > 4: "+" not meaningful for factors in: Ops.factor(qs[i],
> > .minus(x[hi[i]], x[lo[i]]) * (index[i] - lo[i]))
> > >
> >
> >Could anybody tell me, what's going on, please? I have no clue
> >what "^", ">", etc. means.
> >
> > Thanks a lot (and thanks for your patience)
> >
> > Matej
>
> -----------------------------------------------------
> John Fox
> Department of Sociology
> McMaster University
> Hamilton, Ontario, Canada L8S 4M4
> email: jfox at mcmaster.ca
> phone: 905-525-9140x23604
> web: www.socsci.mcmaster.ca/jfox
> -----------------------------------------------------
>
>
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