Greene, Erich J. “A SAS Macro for Covariate-Constrained Randomization of General Cluster-Randomized and Unstratified Designs”. Journal of Statistical Software, Code Snippets 77, no. 1 (April 3, 2017): 1–20. Accessed April 27, 2024. https://www.jstatsoft.org/index.php/jss/article/view/v077c01.