[R] [NB] lm problems

[John Fox]

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
-----------------------------------------------------

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._