[R] Why can't Anove (car package) see the data?

[John Fox]

Dear Patrick,

It's difficult for me to tell from your description what the specific 
nature of the problem is, though it seems to be some kind of scoping issue.

I've experimented a bit and found that the call to update (indirectly) from 
Anova.glm (with LR type-II tests) seems to cause problems:

     > fun.1 <- function(df){
     +     mod <- glm(partic != 'not.work' ~ hincome + children + region,
     +         data=df, family=binomial)
     +     Anova(mod)
     +     }
     > fun.1(Womenlf)
     Error in eval(expr, envir, enclos) : numeric envir arg not of length one
     > traceback()
     16: eval(predvars, data, env)
     15: model.frame.default(formula = partic != "not.work" ~ children +
             region, data = df, drop.unused.levels = TRUE)
     14: model.frame(formula = partic != "not.work" ~ children + region,
             data = df, drop.unused.levels = TRUE)
     13: eval(expr, envir, enclos)
     12: eval(mf, parent.frame())
     11: glm(formula = partic != "not.work" ~ children + region, family = 
binomial,
             data = df)
     10: eval(expr, envir, enclos)
     9: eval(call, parent.frame())
     8: update.default(mod, eval(parse(text = paste(".~.-", 
paste(c(names[term],
         rels), collapse = "-")))))
     7: update(mod, eval(parse(text = paste(".~.-", paste(c(names[term],
         rels), collapse = "-")))))
     6: Anova.II.LR.glm(mod)
     5: switch(test.statistic, LR = Anova.II.LR.glm(mod), Wald = 
Anova.II.Wald.glm(mod),
         F = Anova.II.F.glm(mod, error, error.estimate))
     4: switch(type, II = switch(test.statistic, LR = Anova.II.LR.glm(mod),
         Wald = Anova.II.Wald.glm(mod), F = Anova.II.F.glm(mod, error,
             error.estimate)), III = switch(test.statistic, LR = 
Anova.III.LR.glm(mod),
         Wald = Anova.III.Wald.glm(mod), F = Anova.III.F.glm(mod,
             error, error.estimate)))
     3: Anova.glm(mod)
     2: Anova(mod)
     1: fun.1(Womenlf)

(This uses the Womenlf data frame in the car package.)

In contrast, Anova.lm, which doesn't call update, works OK:

    > fun.2 <- function(df){
     +     mod <- lm(prestige ~ income + education, data=df)
     +     Anova(mod)
     +     }
     > fun.2(Prestige)
     Anova Table (Type II tests)

     Response: prestige
             Sum Sq Df F value    Pr(>F)
     income    2248.1  1  36.856 2.355e-08
     education 8577.3  1 140.615 < 2.2e-16
     Residuals 6038.9 99
     >

(using the Prestige data frame, again in car.)

I don't see an immediate way around the problem, but I'll think about it. 
In addition, if you send me some more information -- the data that you were 
using, the model that you fit, the function from which you called Anova -- 
I'll take a look a it. I'm leaving town for several days tomorrow. If you 
send me the information before then, I'll take it with me.

I'm sorry that you're experiencing this problem,
  John

At 03:14 PM 8/14/2002 +1200, Patrick Connolly wrote:
>At the end of the 'Details:' section of the help on Anova (car
>package), it states:
>
>      The standard R `anova' function calculates sequential (type-I)
>      tests. These rarely test meaningful hypotheses.
>
>So I thought I'd try it.  However, I was perplexed to get this
>message:
>
>Browse[1]> Anova.glm(leaf.glm1, type ="II")
>Error in terms.formula(formula, data = data) :
>         Object "use.df" not found
>
>The regular anova function can find use.df.  What could make it
>invisible to Anova?  I thought it might be because terms.formula took
>an argument x and I already had an object x, but changing its name
>didn't help.  I spent some time searching the archives but found no
>mention of this problem.  I read some of the car package help files,
>but didn't notice a reference to what is different in the way data is
>seen.
>
>The example given in the help file does work, but it uses a data
>object which is in the working directory.  That's not practicable
>within a function.  So I'd appreciate other ideas.
>
>platform i686-pc-linux-gnu
>arch     i686
>os       linux-gnu
>system   i686, linux-gnu
>status
>major    1
>minor    5.1
>year     2002
>month    06
>day      17
>language R
>
>Thanks
>
>--
>Patrick Connolly
>HortResearch
>Mt Albert
>Auckland
>New Zealand
>Ph: +64-9 815 4200 x 7188
>~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~
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>
>
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-----------------------------------------------------
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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