Maybe a very, very basic question but how can I get a vector of values with the specific format: 001,002,010,100 instead of: 1,2,10,100 Paulo
________________________________ De: [EMAIL PROTECTED] em nome de Stephan Moratti Enviada: seg 05-05-2008 11:43 Para: r-help@r-project.org Assunto: Re: [R] Validating a mixed-effects model Hi Armin, Alternatively you could use premutation statistics. You could shuffle your subjects between groups randomly under the Null hypothesis of no differences between groups and each time claculating the lme model. I am not sure, but if you do it at each time point of your repetition at each draw, then you could remember the greates F value for your F-value distribution. This could control the multiple comparison problem. Then after let's say 1000 draws you have a F value distribution under the Null hypothesis and you could determine your critical F value from that distribution. Hope that helps, Stephan Armin wrote: Hi I constructed a mixed-effects model from longitudinal repeated measurements of lab values in 22 patients seperated into two groups with the groups as fixed effect using lme. I thought about using the jackknife procedure, i. e., removing any one subject and calculating the fixed effect, to assess the stability of the fixed effect and thereby validate the model. I suppose this has been done in the following study: http://content.nejm.org/cgi/content/full/357/19/1903 (this may be restricted access, sorry) Is such an approach feasible? Also in the article results are confirmed by comparing the mixed model with a fitted least-squares regression. I understand that this can be achieved with lmlist, but only for for models without an additional fixed effect!? Are there any other good approaches to validate a mixed-effects model that will be accepted in medical peer review? -- *Stephan Moratti, PhD/ /**/see also: http://web.mac.com/smoratti/ /*Centro de Tecnología Biomédica CBT, Universidad Politécnica de Madrid, en la actualidad (currently at) en el Centro de Magnetoencefalografía Dr. Perez Modrego, Universidad Complutense de Madrid, Faculdad de Medicina, Pabellón 8, Avda. Complutense, s/n, 28040 Madrid, Spain, email: [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> [EMAIL PROTECTED] Tel.: +34 91 394 2292 Fax.: +34 91 394 2294 */ /* ______________________________________________ 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. [[alternative HTML version deleted]]
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