I want to specify a 2-level mixed model using the lme function in order to test an a priori hypothesis about the between-group values of the slopes but don't know how to do this . Here is the problem.
Consider first the case of a single group. The model is: Y_i= a +bX_i + error where I indexes the different values of X and Y in this group . The a priori hypothesis of the slope is: b=K. This is easily tested with a t-test (b-K=0). Now imagine that there are j groups. For each group j the model is: Y_ij= a_j + b_jX_ij + error. Both the intercepts (a) and the slopes (b) are allowed to vary between groups. The a priori (null) hypothesis of interest involved the between-group values of the slopes and is: b_j=Kj where Kj is specified a priori for each group j based on theoretical considerations but whose values differ between groups. This is clearly a mixed-model problem. I know how to specify the model in lme but I don't know how to set up the inferential test that b_j=Kj for all j groups versus the alternative hypothesis that b_j is not equal to Kj for at least one group. Any help in explaining how to do this using the mle function in R is appreciated. Thanks. Bill Shipley Département de biologie Université de Sherbrooke Sherbrooke (Québec) J1K 2R1 (819) 821-8000, 62079 (819) 821-8049 (Fax) NEW! Shipley, B. (2010). From plant traits to vegetation structure: Chance and selection in the assembly of ecological communities. Cambridge University Press. http://www.amazon.com/Plant-Traits-Vegetation-Structure-Communities/dp/05211 33556/ref=sr_1_3?ie=UTF8&s=books&qid=1260148938&sr=1-3 ______________________________________________ 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.