I am using Stata 7 (using the executable last update, 6/11/02) on a PC.
For -xtlogit, re- the manual says (p.380) that the value of rho is computed as
rho = sigma2_u / [sigma2_u + 1]
The numbers in the union example given in that page confirm that.
However, I have a dataset where I'm measuring platelet aggregation (yes/no)
as a function of the concentration of a substance that is added. When I run
a RE logistic model,
xtlogit agg aaconc, re i(subj)
the rho computed manually (0.70) does not agree with the value shown in the
output (0.41). I'm stumped!
Thanks for any insights.
Random-effects logit Number of obs = 110
Group variable (i) : subj Number of groups = 68
Random effects u_i ~ Gaussian Obs per group: min = 1
avg = 1.6
max = 4
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