On 20.11.2011 12:46, tujchl wrote:
HI I use glm in R to do logistic regression. and treat both response and predictor as factor In my first try: ******************************************************************************* Call: glm(formula = as.factor(diagnostic) ~ as.factor(7161521) + as.factor(2281517), family = binomial()) Deviance Residuals: Min 1Q Median 3Q Max -1.5370 -1.0431 -0.9416 1.3065 1.4331 Coefficients: Estimate Std. Error z value Pr(>|z|) (Intercept) -0.58363 0.27948 -2.088 0.0368 * as.factor(7161521)2 1.39811 0.66618 2.099 0.0358 * as.factor(7161521)3 0.28192 0.83255 0.339 0.7349 as.factor(2281517)2 -1.11284 0.63692 -1.747 0.0806 . as.factor(2281517)3 -0.02286 0.80708 -0.028 0.9774 --- Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 (Dispersion parameter for binomial family taken to be 1) Null deviance: 678.55 on 498 degrees of freedom Residual deviance: 671.20 on 494 degrees of freedom AIC: 681.2 Number of Fisher Scoring iterations: 4 ******************************************************************************* And I remodel it and *want no intercept*: ******************************************************************************* Call: glm(formula = as.factor(diagnostic) ~ as.factor(2281517) + as.factor(7161521) - 1, family = binomial()) Deviance Residuals: Min 1Q Median 3Q Max -1.5370 -1.0431 -0.9416 1.3065 1.4331 Coefficients: Estimate Std. Error z value Pr(>|z|) as.factor(2281517)1 -0.5836 0.2795 -2.088 0.0368 * as.factor(2281517)2 -1.6965 0.6751 -2.513 0.0120 * as.factor(2281517)3 -0.6065 0.8325 -0.728 0.4663 as.factor(7161521)2 1.3981 0.6662 2.099 0.0358 * as.factor(7161521)3 0.2819 0.8325 0.339 0.7349 --- Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 (Dispersion parameter for binomial family taken to be 1) Null deviance: 691.76 on 499 degrees of freedom Residual deviance: 671.20 on 494 degrees of freedom AIC: 681.2 Number of Fisher Scoring iterations: 4 ******************************************************************************* *As show above in my second model it return no intercept but look this: Model1: (Intercept) -0.58363 0.27948 -2.088 0.0368 * Model2: as.factor(2281517)1 -0.5836 0.2795 -2.088 0.0368 ** They are exactly the same. Could you please tell me what happen?
Actually it does not make sense to estimate the model without an intercept unless you assume that it is exactly zero for the first levels of your factors. Think about the contrasts you are interested in. Looks like not the default?
Uwe Ligges
Thank you in advance -- View this message in context: http://r.789695.n4.nabble.com/logistic-regression-by-glm-tp4088471p4088471.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@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.
______________________________________________ R-help@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.
