**Generalized estimating equations (GEE)**

A preliminary GEE method with an independent correlation assumption relates to the standard PML method where observations are assumed independent within clusters for the estimation of the regression coefficients, but are allowed to be correlated for the estimation of the covariance matrix of the estimated regression coefficients. In a more advanced GEE method, assuming an exchangeable correlation structure, observations are allowed to be correlated within clusters in the estimation of both regression coefficients and the covariance matrix of estimated regression coefficients. See pages 287-289 in Lehtonen, R & Pahkinen, E. (2004)