Dear Martin, How many levels has PLANT? Does it is an ID for the individual plants? In that case it is pointless to add it to a random effect. Because then each group at the higest level would contain only one observation.
There is a mailing list dedicated to mixed effects models: R-Sig-mixed-models. HTH, Thierry ---------------------------------------------------------------------------- ir. Thierry Onkelinx Instituut voor natuur- en bosonderzoek / Research Institute for Nature and Forest Cel biometrie, methodologie en kwaliteitszorg / Section biometrics, methodology and quality assurance Gaverstraat 4 9500 Geraardsbergen Belgium tel. + 32 54/436 185 [EMAIL PROTECTED] www.inbo.be To call in the statistician after the experiment is done may be no more than asking him to perform a post-mortem examination: he may be able to say what the experiment died of. ~ Sir Ronald Aylmer Fisher The plural of anecdote is not data. ~ Roger Brinner The combination of some data and an aching desire for an answer does not ensure that a reasonable answer can be extracted from a given body of data. ~ John Tukey -----Oorspronkelijk bericht----- Van: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Namens HENERY Martin Verzonden: donderdag 27 november 2008 13:29 Aan: r-help@r-project.org Onderwerp: [R] lmer refuses nested random factors I am trying to run the following model in R > lmer(leaves.eaten~Geocytotype+(1|TEST/ PLANT),data=cyphoplantfeeding,family=poisson) My experimental setup is 41 replicates (TEST) of an experiment in which there are three Geocytotypes of a plant species in each TEST, and two plant pseudoreplicates per Geocytotype in each test (i.e. 3*2=6 plants per test). So my random factors are trying to examine/ account for variation between replicates and between pairs of plants in each test. The response variable is counts of damaged leaves on each plant hence the poisson distribution. When I try and run the model I get this error message (sorry but it is in French): >Erreur : length(f1) == length(f2) is not TRUE >De plus : Warning messages: >1: In PLANT:TEST : > l'expression numérique a 246 éléments : seul le premier est utilisé >2: In PLANT:TEST : > l'expression numérique a 246 éléments : seul le premier est utilisé This however is not connected as far as I can tell to the structure of the data because I checked the lengths of all the variables and if I run the same model design using lme function (without the family=poisson of course) and the model computes perfectly fine with the correct group sizes: >Number of Observations: 246 >Number of Groups: > TEST PLANT %in% TEST > 41 123 I couldn't find this error mentioned in any other posts on the list. Can someone enlighten me as to how to get around this intractable problem? My crude solution is to go around the obstacle by computing the mean of each plant pair and using a GLM with poisson distribution and ignore random effects. Martin ************************************************************************ Martin Henery Post doctoral researcher Département de Biologie/Ecologie & Evolution Université de Fribourg ************************************************************************ [[alternative HTML version deleted]] Dit bericht en eventuele bijlagen geven enkel de visie van de schrijver weer en binden het INBO onder geen enkel beding, zolang dit bericht niet bevestigd is door een geldig ondertekend document. The views expressed in this message and any annex are purely those of the writer and may not be regarded as stating an official position of INBO, as long as the message is not confirmed by a duly signed document. ______________________________________________ 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.
