[R] Repeated measures cummulative logit mixed model

[Jim Trabas]

Dear R help gurus, 


I have the following problem and I would be delighted if you could help me.

>From a large (1500) cohort of patients we have been taking some measurements
(ECG measurements, but its not important). The measurements are ordinal in 4
grades (Grade I-IV, grade IV being the most severe form). Every patients has
been measured several times (usually once per year). The follow-ups are
different for each patient (ranging from days to several years), thus some
patients have only 1 measurement and some have several. A patient can shift
from Grade to Grade, that is a patient can be measured now as Grade I and
later as Grade II and then at then next measurement he can return to Grade
I.

My data are in the following format

Patient ID, Time of Measurement, Grade

I would like to model the probability of being in each of the Grades (I-V)
as a function of time. I guess i require a repeated measure cumulative logit
mixed model with random slope and intercept (for each patient).

Could anyone pin point me at any information that would help me accomplish
this in R? Packages? Books?

Information about categorical data analysis with R seems to be poor in the
Internet.

Thank you very much on advance
JT

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