An empirical comparison of several clustered data approaches under confounding due to cluster effects in the analysis of complications of coronary angioplasty.
Berlin JA, Kimmel SE, Ten Have TR, Sammel MD. An empirical comparison of several clustered data approaches under confounding due to cluster effects in the analysis of complications of coronary angioplasty. Biometrics. 1999 Jun; 55(2):470-6.