I'm new R-programming user, I need to use gam function. y<-gam(a~s(b),family=gaussian(link=log),data) y<-gam(loga~s(b), family =gaussian (link=identity),data) why these two command results are different? I guess these two command results are same, but actally these two command results are different, Why? -- View this message in context: http://r.789695.n4.nabble.com/please-help-what-are-the-different-using-log-link-function-and-log-transformation-tp3608931p3608931.html Sent from the R help mailing list archive at Nabble.com.
please help! what are the different using log-link function and log transformation?
4 messages · pigpigmeow, Rubén Roa, Bill Venables
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The two commands you give below are certain to lead to very different results, because they are fitting very different models. The first is a gaussian model for the response with a log link, and constant variance. The second is a gaussian model for a log-transformed response and identity link. On the original scale this model would imply a constant coefficient of variation and hence a variance proportional to the square of the mean, and not constant. Your problem is not particularly an R issue, but a difficulty with understanding generalized linear models (and hence generalized additive models, which are based on them). Bill Venables.
From: r-help-bounces at r-project.org [r-help-bounces at r-project.org] On Behalf Of pigpigmeow [glorykwok at hotmail.com]
Sent: 19 June 2011 17:39
To: r-help at r-project.org
Subject: [R] please help! what are the different using log-link function and log transformation?
Sent: 19 June 2011 17:39
To: r-help at r-project.org
Subject: [R] please help! what are the different using log-link function and log transformation?
I'm new R-programming user, I need to use gam function. y <- gam(a ~ s(b), family = gaussian(link=log), data) y <- gam(log(a) ~ s(b), family = gaussian (link=identity), data) why [do] these two command [give different] results? I guess these two command results are same, but actally these two command results are different, Why? -- View this message in context: http://r.789695.n4.nabble.com/please-help-what-are-the-different-using-log-link-function-and-log-transformation-tp3608931p3608931.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help at 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.
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