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From |
Laurel.Copeland@med.va.gov |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: Assess interfacility variation with xtlogit sigma_u |

Date |
Wed, 27 Aug 2003 15:01:29 -0400 |

A researcher here would like to assess interfacility variation in the receipt of benzodiazepines by depressed patients. Another colleague suggested using xtlogit, remarking that "sigma_u gives you the facility level standard deviation in the log odds of benzo use w. a standard error and 95% confidence interval on the facility level standard deviation." I obtained the data from the first researcher and ran the analysis suggested. How do we interpret the results? The sigma_u obtained is 0.34 (SE=.014), as shown below. Is this a lot? a little? What does the standard deviation in the log odds of something represent, how big might it be (range), what else needs to be considered with it in order for its value to have meaning, etc.? There are 128,029 patients at 134 facilities. Thank you very much, Laurel . use c:\adherence\forlaurel . desc Contains data from c:\adherence\forlaurel.dta obs: 128,029 vars: 3 size: 2,048,464 (99.0% of memory free) ---------------------------------------------------------------------------- -- storage display value variable name type format label variable label ---------------------------------------------------------------------------- -- facility float %9.0g first 3 digits of stn_num anybenzo float %9.0g 1 = Used Benzodiazepine ID float %9.0g Patient ID ---------------------------------------------------------------------------- -- Sorted by: . xtlogit anybenzo, i(facility) Fitting comparison model: Iteration 0: log likelihood = -79880.821 Fitting full model: tau = 0.0 log likelihood = -64723.911 tau = 0.1 log likelihood = -63736.488 tau = 0.2 log likelihood = -63760.93 Iteration 0: log likelihood = -63736.488 Iteration 1: log likelihood = -63736.218 Iteration 2: log likelihood = -63736.197 Iteration 3: log likelihood = -63736.195 Random-effects logistic regression Number of obs = 121643 Group variable (i): facility Number of groups = 134 Random effects u_i ~ Gaussian Obs per group: min = 9 avg = 907.8 max = 3206 Wald chi2(0) = 0.00 Log likelihood = -63736.195 Prob > chi2 = . ---------------------------------------------------------------------------- -- anybenzo | Coef. Std. Err. z P>|z| [95% Conf. Interval] -------------+-------------------------------------------------------------- -- _cons | -.5480285 .0246479 -22.23 0.000 -.5963374 -.4997196 -------------+-------------------------------------------------------------- -- /lnsig2u | -2.151144 .0837696 -2.31533 -1.986959 -------------+-------------------------------------------------------------- -- sigma_u | .3411026 .014287 .3142191 .3702861 rho | .0341584 .0027637 .029137 .0400095 ---------------------------------------------------------------------------- -- Likelihood-ratio test of rho=0: chibar2(01) = 3.2e+04 Prob >= chibar2 = 0.000 Note: 34 completely determined panels Laurel A Copeland, PhD VA Ann Arbor Health System (734) 769-7100 x6206 * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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