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...e a positive effect on probability of selection, but then a negative effect on the outcome variable. i.e. Model<-selection(participation~age, frequency~age, ...) Documentation elsewhere describes one method for doing this in Stata based on Sigelman and Zeng: http://polisci.osu.edu/prl/Selection%20Models.pdf - see page 16. I'd like to replicate this in r, but wanted to check I'm not reinventing the wheel, before doing so. Any help is much appreciated. Best regards Mark [[alternative HTML version deleted]]

...and 'y' lengths differ" Can anyone shed some light please? I am basically copying the methods of the pdf entitled "Linear mixed models in R" by S?ren Feodor Nielsen 20003. http://cran.r-project.org/doc/contrib/Fox-Companion/appendix-mixed-models.pdf#search=%22Linear%20mixed%20models%20in%20R%22 Simon Pickett PhD student Centre For Ecology and Conservation Tremough Campus University of Exeter in Cornwall TR109EZ Tel 01326371852

Hello, Having measured two populations' characteristics at one particular time[with great precision] with R, I would like to extend this to measuring the same populations starting at t1, and then again at t2, and try to develop a growth model (something like dpop1/dt=r*pop^(...),dpop2/dt=r*pop^(...)). I think the idea is to create a model that will predict the growth of a population(N(mu,

...I hope that some significant predictors like height and root length would help define a plant's likely number of flowers. There's a good basic outline of the model I'm trying to make( it is about bears populations changing over time): www.fish.washington.edu/.../Stochastic%20Population%20Models.ppt It's just that it seems someone else may have started a path in this direction in connection with R or another software, ... -s [[alternative HTML version deleted]]