effect function (effects package)
Dear Eileen, You apparently misunderstand what the effect() function does; it computes fitted values and their standard errors under the model (by default in a GLM on the scale of the response) at specific combinations of values of the predictors (e.g., letting two interacting predictors range over their combinations of values while others are held to their means). Details are provided in the references given in ?effect; see in particular the 2003 Journal of Statistical Software article at <http://www.jstatsoft.org/v08/i15>. I hope this helps, John -------------------------------- John Fox Senator William McMaster Professor of Social Statistics Department of Sociology McMaster University Hamilton, Ontario, Canada http://socserv.mcmaster.ca/jfox
-----Original Message----- From: r-help-bounces at r-project.org [mailto:r-help-bounces at r- project.org] On Behalf Of Hlavka, Eileen Sent: February-04-12 1:56 AM To: r-help at r-project.org Subject: [R] effect function (effects package) Dear all, How does the effect() function in the effects package calculate effects and standard errors for glm quasipoisson models? I was using effect() to calculate the impact of increasing x to e + epsilon, and then finding the expected percent change. I thought that this effect (as a percentage) should be exp(beta*epsilon), where beta is the appropriate coefficient from the model, but that's not what I'm getting using the effect() output. Sorry for the lack of example-it would require toy data etc. and seems unnecessary since my question is more conceptual. Thanks, Eileen
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