[R] Help with problem - multilevel model?

From: Crabb, David <David.Crabb.1_at_city.ac.uk>
Date: Thu 18 Jan 2007 - 14:15:45 GMT

I have what is probably a very simple problem but I would be very grateful to the list for any help or pointers to implement a solution in R.

We have two types of measurements on the eye that we have collected in 62 patients at 5 fixed time points during a clinical visit over an office day. We want to establish if there is an association between the measurements. Obviously it would be wrong to generate a simple scatterplot of all 62*5 observations and consider something like a simple correlation coefficient. What I really need is to set up a 2-level model with measurements nested within patients and use, perhaps, one variable as a response and the other as a predictor. I would also like to add in time of day (probably as a categorical) to check this isn't affecting things. I haven't used multi-level modelling in R and wonder how I can simply go about fitting this model and looking at the significance of the estimates in R. I also have a plot in my mind - 62 little regression lines (n=5) and think that this might be informative.....

Any help or pointers will be gratefully received - Many Thanks.

Dr. David Crabb
Department of Optometry and Visual Science, City University, Northampton Square, London EC1V OHB Tel: 44 207 040 0191 d.crabb@city.ac.uk http://www.city.ac.uk/optometry/about/staff/crabb.html

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