Dear all, Thanks to everyone who replied off list to my (rambling) question earlier this year! I have put pointers to things I found useful over here:
http://tinyurl.com/yvvvn9 Thought it might be helpful to share as now and again I receive emails from people wondering if I ever made progress. Best wishes, Andy On 25 Feb 2007, at 19:58, Andy Fugard wrote: > Dear all, > > I'm struggling to find the best (set of?) function(s) to do repeated > measures logistic regression on some data from a psychology > experiment. > > An artificial version of the data I've got is as follows. Firstly, > each participant filled in a questionnaire, the result of which is a > score. > >> questionnaire > ID Score > 1 1 6 > 2 2 5 > 3 3 6 > 4 4 2 > ... > > Secondly, each participant did a task which required a series of > button-pushes. The response is binary. The factors CondA and CondB > describe the structure of the stimulus: > >> experiment > ID CondA CondB Response > 1 1 a1 b1 1 > 2 1 a2 b2 0 > 3 1 a3 b1 0 > 4 1 a4 b2 0 > 5 1 a1 b1 1 > 6 1 a2 b2 0 > 7 1 a3 b1 0 > 8 1 a4 b2 0 > 9 2 a1 b1 1 > 10 2 a2 b2 0 > 11 2 a3 b1 0 > 12 2 a4 b2 0 > 13 2 a1 b1 1 > 14 2 a2 b2 0 > 15 2 a3 b1 0 > 16 2 a4 b2 0 > > I would like to model how someone's score on the questionnaire > relates to the responses they give in the button-pushing. I'm > particularly interested in interactions between the type of the > stimulus and the score. > > I combined the experiment and the questionnaire dataframe with a > merge so now there an additional column. > >> exp.q > ID Score CondA CondB Response > 1 1 6 a1 b1 1 > 2 1 6 a2 b2 0 > 3 1 6 a3 b1 0 > 4 1 6 a4 b2 0 > 5 1 6 a1 b1 1 > 6 1 6 a2 b2 0 > 7 1 6 a3 b1 0 > 8 1 6 a4 b2 0 > 9 2 5 a1 b1 1 > 10 2 5 a2 b2 0 > 11 2 5 a3 b1 0 > 12 2 5 a4 b2 0 > ... > > Eventually, via glm, glmmPQL, and a few others, I ended up with > lmer. My questions follow. I suspect (or hope) that I need to be > pointed towards the relevant literature. I own Faraway's "Extending > the Linear Model with R" and Crawley's "Statistics: An Introduction > using R". > > 1. Is the way I've combined the tables okay? I'm concerned that the > repetition of the score is Bad but can't think of any other way to > code things. > > 2. Is lmer the most appropriate function to use? > > 3. If so, does the following call capture what I'm trying to model? > > model1 = lmer(Response ~ CondA * CondB * Score + (1|Subject), > data =exp.q, > family = binomial) > > I just want to tell lmer, "Look, this set of responses all comes from > the same person: tell me the within-subject stuff that's going on and > how that's affected by their score!" > > 4. Is there any way to do stepwise model simplification? In the real > data I have, there are several more predictors, including more than > one questionnaire score and subscores. I have specific hypotheses > about what could be going on, so I can live with manual editing of > the formulae, but it's nice for exploratory purposes to do stepwise > simplification. > > 5. What's the best way to discover and report the relative > contribution of each predictor? I'm after an analogue of > standardized betas (though I recently learned that they're thoroughly > evil). > > 6. Is there anyway to get a p-value for goodness of fit? > > Many thanks for any help, > > Andy > > -- > Andy Fugard, Postgraduate Research Student > Psychology (Room F15), The University of Edinburgh, > 7 George Square, Edinburgh EH8 9JZ, UK > Mobile: +44 (0)78 123 87190 http://www.possibly.me.uk > > ______________________________________________ > [EMAIL PROTECTED] 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. -- Andy Fugard, Postgraduate Research Student Psychology (Room F15), The University of Edinburgh, 7 George Square, Edinburgh EH8 9JZ, UK Mobile: +44 (0)78 123 87190 http://www.possibly.me.uk ______________________________________________ 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.
