David Winsemius wrote: > > On Nov 26, 2009, at 12:14 PM, JVezilier wrote: > >> >> Hello !! >> >> I'm recently having a debate with my PhD supervisor regarding how to >> write >> the result of a likelihood ratio test in an article I'm about to submit. >> >> I analysed my data using "lme" mixed modelling. >> >> To get some p-values for my fixed effect I used model simplification >> and the >> typical output R gives looks like this: >> >> model2 = update ( model1,~.-factor A) >> anova (model1, model2) >> >> Model df AIC BIC logLik Test >> L.Ratio p-value >> model 1 1 26 -78.73898 15.29707 65.36949 >> model 2 2 20 -73.70539 -1.36997 56.85270 1 vs 2 17.03359 >> 0.0092 >> >> I thought about presenting it very simply copying/pasting R table and >> writing it like: "factor A had a significant effect on the response >> variable >> (Likelihood ratio test, L-ratio = 17.033, p = 0.0092)" >> >> But my boss argued that it's too unusual (at least in our field of >> evolutionary biology) and that I should present instead the LR statistic >> together with the corresponding Chi^2 statistic since the likelihood >> ratio >> is almost distributed like a Chi2 (df1-df2), and then write down the >> p-value >> corresponding to this value of Chi. >> >> I looked up in the current litterature but cannot really find a proper >> answer to that dilmena. >> >> So, dear evolutionary biologists R users, how would you present it ? > > I am not an evolutionary biologist, but presumably your supervisor is > one. Why are you picking a fight not only with him but with your > prospective audience when there is no meaningful difference? Here is the > p-value you would get with his method: > >>> 1-pchisq( 2*(65.36949 - 56.85270), df=6) > [1] 0.009160622 >
As I understood the question, it *is* purely formalistic. I.e., what to write, not what to do. I'd say "L-ratio" is plain wrong, since this is not a ratio, but the log of a ratio. "-2lnQ" or "-2logQ" is what my old teachers would write, but pragmatically, I'd expect the best chances with editors and reviewers to be "LRT: chi-square=17.03, df=6, p=0.092", possibly with LRT spelled out. (Some journals like to have the df because it allows reviewers to catch glaring mistakes like categorical variables treated as numeric.) -- O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - (p.dalga...@biostat.ku.dk) FAX: (+45) 35327907 ______________________________________________ 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.
