P Sellaz

less info
reputation
1418
bio website location age member for 2 years, 1 month seen Oct 25 at 18:44 profile views 76

142 Actions

 Mar30 comment Sampling with inclusion/exclusion criteria from known distribution Great. Thank you. Mar30 accepted Sampling with inclusion/exclusion criteria from known distribution Mar30 comment Sampling with inclusion/exclusion criteria from known distribution Thanks cardinal - the second one is correct (we are seeking a fixed sample size of observations meeting the criteria). So far I have just used the U(25,30) distribution as a guestimate, which I expect will not be far from correct, and simulations show that to be the case, but I'd like to know a more rigorous theory-based answer, if possible. Mar30 asked Sampling with inclusion/exclusion criteria from known distribution Mar26 accepted Weibull moment generating function and Gamma function Mar26 comment Weibull moment generating function and Gamma function Thank you. So, it's just: $E(X^r)=\int_{0}^{\infty }(u^{1\beta})^r e^{-u} du$ And then the required result follows immediately. It seems too easy ! ! It's great, but have I missed anything ? Mar26 asked Weibull moment generating function and Gamma function Feb18 comment Sampling distribution of random effects estimator Am I right in thinking that's what is going on here: example(mcmcsamp);densityplot(samp0);qqmath(samp0) ? Feb18 comment Sampling distribution of random effects estimator Not exactly what you want, but see bottom of p18 here for some more details: lme4.r-forge.r-project.org/book/Ch1.pdf Jan18 accepted Finding a trend in variance Jan18 comment Finding a trend in variance OK. Thanks again for your help. Much appreciated. Jan18 comment Finding a trend in variance Hi again. Sorry that I'm not explaining it very well. It's not that the variance of any particular variable has a trend. It's the variance of the hospital-level effects (random effects) that has a trend. It is hypothesized that the variation in hospital-level effects has decreased linearly over the period of the data, due to more /consistency/ in clinical diagnosis and treatment (not necessarily /better/ treatment/outcomes, though that is also likely, but not the point). Jan18 comment Finding a trend in variance ...Cont... At this point I am searching for published papers, in any field/discipline, where a trend in variance has been modeled at level 1 in a multilevel model. So far I have not found any, but I am pretty sure that there should be some. If anyone can point me in the right direction, or provide links to published research I would be very grateful. Jan18 comment Finding a trend in variance Thank you. I'll mark this as the accepted answer soon. First, if you don't mind I'd like to ask a related question which refers to the points @whuber and yourself made. I asked about this because it arose as a consequence of other modelling I am doing. The /real/ problem is described in this open question: stats.stackexchange.com/questions/19911/… It is thought that there has been a near-linear change in randoms effects variance, and that is actually what I'm eventually hoping to model. Cont...... Jan17 comment Finding a trend in variance Hi Erik and thanks. You know, I almost posted the question on mapleprimes, not SE ! I ran your code and also got good results, albeit with a "Warning, undefined value encountered" Jan17 comment Finding a trend in variance Thank you very much for those suggestions - I will look into them :) Jan17 comment Finding a trend in variance Thanks for your comment. It seems to be trivial to you, but it's unwieldy to me and I don't know how to solve such equations in R. Jan17 comment Finding a trend in variance Thanks, but I don't know how to do that in R. Wouldn't the likelihood function would be unwieldy with n=1000 ? I fiddled around a little in Maple and didn't have much success there either. Jan17 asked Finding a trend in variance Jan16 answered Introduction to structural equation modeling