In semiparametric ANOCOVA (mixed-effects) models, the role of regression rank scores in robust estimation of fixed-effects parameters as well as covariate regression functionals is critically appraised, and the relevant asymptotic theory is presented.
"Regression rank scores estimation in ANOCOVA." Ann. Statist. 24 (4) 1586 - 1601, August 1996. https://doi.org/10.1214/aos/1032298286