Højsgaard S, Halekoh U, Yan J. The R Package geepack for Generalized Estimating Equations. J. Stat. Soft. [Internet]. 2005 Dec. 22 [cited 2024 Nov. 21];15(2):1-11. Available from: https://www.jstatsoft.org/index.php/jss/article/view/v015i02