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| From | Robert Sutter <rdsutterjr@gmail.com> |
| To | Statalist <statalist@hsphsun2.harvard.edu> |
| Subject | st: Poisson Two Level Random Intercept ICC |
| Date | Fri, 1 Mar 2013 11:20:57 -0600 |
How is the intraclass correlation coefficient calculated when using a
two level random intercept model?
Below is the output from a two level model for the count of excess
deaths (oediff2) as the dependent variable and the clusters are
attending physicians. sigma_u is the random intercept variance.
In Rabe-Hesketh’s book the ICC for binary data is derived by the
following formula:random intercept variance/( random intercept
variance + π2/3). π2/3 represents the variance of the logistic
distribution.
Can the same formula be used for count data by replacing π2/3 with
the variance of oediff2?
xtpoisson oediff2, i(attending_phy_id) normal
Random-effects Poisson regression Number of obs = 75
Group variable: attending_ph~d Number of groups = 75
Random effects u_i ~ Gaussian Obs per group: min = 1
avg = 1.0
max = 1
Wald chi2(0) = .
Log likelihood = -213.3618 Prob > chi2 = .
------------------------------------------------------------------------------
oediff2 | Coef. Std. Err. z P>|z|
[95% Conf. Interval]
-------------+----------------------------------------------------------------
_cons | 2.617512 .0323429 80.93 0.000 2.554121 2.680903
-------------+----------------------------------------------------------------
/lnsig2u | -5.924562 4.653182 -1.27 0.203 -15.04463 3.195508
-------------+----------------------------------------------------------------
sigma_u | .0517009 .1202868 .0005409 4.94192
------------------------------------------------------------------------------
Thanks,
Bob
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