The data are from a multicenter randomized clinical trial to compare test and control treatments for the management of chronic pain, and they have had previous consideration in Stokes et al. (2000, chap. 13).
data(cpain)
A data frame with 193 observations and 4 variables
treat
a factor with levels active
and placebo
for treatment
response
a factor with five levels poor
, fair
, moderate
, good
and excel
for pain status after treatment for 4 weeks
center
a factor with two levels I
and II
for two centers
diagnosis
a factor with four levels A
, B
, C
, and D
for diagnoses
Stokes, M. E., Davis, C. S., and Koch, G. G. (2000), Categorical Data Analysis using the SAS System, Cary: SAS Publishing.