Re: [R] interpreting interactions in a model
The Predict.Plot function in the TeachingDemos package can help you visualize interactions. It will work best if Month is treated as a continuous variable. -- Gregory (Greg) L. Snow Ph.D. Statistical Data Center Intermountain Healthcare greg.s...@imail.org 801.408.8111 -Original Message- From: r-help-boun...@r-project.org [mailto:r-help-bounces@r- project.org] On Behalf Of gaiarrido Sent: Wednesday, August 17, 2011 2:57 AM To: r-help@r-project.org Subject: [R] interpreting interactions in a model Hi, I´ve got this model model-glm(prevalence~agesex+agesex:month,binomial) and the output of anova is like that anova(model,test=Chisq) Df Deviance Resid. Df Resid. Dev P(|Chi|) NULL524 206.97 agesex 2 9.9165 522 197.05 0.007025 ** agesex:month9 18.0899 513 178.96 0.034145 * I don´t know how to interpret the interaction agesex:month, my mind doubt between 2 options: a) For a giving group of agesex there are differences between months b)There are differences between groups of agesex in some months but not in others. Which option is correct? Thanks very much - Mario Garrido Escudero PhD student Dpto. de Biología Animal, Ecología, Parasitología, Edafología y Qca. Agrícola Universidad de Salamanca -- View this message in context: http://r.789695.n4.nabble.com/interpreting-interactions-in-a-model- tp3749430p3749430.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.
Re: [R] interpreting interactions in a model
Thanks, I´ve found the differencies with a posteriori tests. I don't put the term month because it is not significant. - Mario Garrido Escudero PhD student Dpto. de Biología Animal, Ecología, Parasitología, Edafología y Qca. Agrícola Universidad de Salamanca -- View this message in context: http://r.789695.n4.nabble.com/interpreting-interactions-in-a-model-tp3749430p3752979.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.
Re: [R] interpreting interactions in a model
Hi: On Wed, Aug 17, 2011 at 1:56 AM, gaiarrido gaiarr...@usal.es wrote: Hi, I´ve got this model model-glm(prevalence~agesex+agesex:month,binomial) and the output of anova is like that anova(model,test=Chisq) Df Deviance Resid. Df Resid. Dev P(|Chi|) NULL 524 206.97 agesex 2 9.9165 522 197.05 0.007025 ** agesex:month 9 18.0899 513 178.96 0.034145 * Where is the month main effect? Even if it's 'not significant', it belongs in the model (principle of marginality). I don´t know how to interpret the interaction agesex:month, my mind doubt between 2 options: a) For a giving group of agesex there are differences between months b)There are differences between groups of agesex in some months but not in others. Which option is correct? In the absence of a reproducible example, no one can say, but it's within the realm of possibility that either or both could be correct. The significance test for interaction indicates *whether* an interaction effect exists - it doesn't tell you *what type* of interaction exists. Conditional on the inference that an interaction effect is present, the next step of the analysis is to investigate the nature of the interaction. This could involve planned contrasts, multiple comparisons, graphics, etc. The car, effects, multcomp and HH packages can be useful for these types of investigations. HTH, Dennis Thanks very much - Mario Garrido Escudero PhD student Dpto. de Biología Animal, Ecología, Parasitología, Edafología y Qca. Agrícola Universidad de Salamanca -- View this message in context: http://r.789695.n4.nabble.com/interpreting-interactions-in-a-model-tp3749430p3749430.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.
