Hi Silvano,
this is FAQ 7.17
http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-does-the-output-from-anova_0028_0029-depend-on-the-order-of-factors-in-the-model_003f
hth.
Silvano schrieb:
Hi,
I have a dichotomous variable (Q1) whose answers are Yes or No.
Also I have 2 categorical explanatory variables (V1 and V2) with two
levels each.
I used logistic regression to determine whether there is an effect of
V1, V2 or an interaction between them.
I used the R and SAS, just for the conference. It happens that there
is disagreement about the effect of the explanatory variables between
the two softwares.
R:
q1 = glm(Q1~grau*genero, family=binomial, data=dados)
anova(q1, test="Chisq")
Df Deviance Resid. Df Resid. Dev P(>|Chi|)
NULL 202 277.82
grau 1 4.3537 201 273.46 0.03693 *
genero 1 1.4775 200 271.99 0.22417
grau:genero 1 0.0001 199 271.99 0.99031
SAS:
proc logistic data=psico;
class genero (param=ref ref='0') grau (param=ref ref='0');
model Q1 = grau genero grau*genero / expb;
run;
Type 3 Analysis of Effects
Wald
Effect DF Chi-Square Pr > ChiSq
grau 1 1.6835 0.1945
genero 1 0.7789 0.3775
genero*grau 1 0.0002 0.9902
The parameters estimates are the same for both.
Coefficients:
Estimate Std. Error z value Pr(>|z|)
(Intercept) 0.191055 0.310016 0.616 0.538
grau 0.562717 0.433615 1.298 0.194
genero -0.355358 0.402650 -0.883 0.377
grau:genero 0.007052 0.580837 0.012 0.990
What am I doing wrong?
Thanks,
--------------------------------------
Silvano Cesar da Costa
Departamento de Estatística
Universidade Estadual de Londrina
Fone: 3371-4346
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--
Eik Vettorazzi
Institut für Medizinische Biometrie und Epidemiologie
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______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
