The purpose of the present investigation is to develop a class of rank order tests for the equality of treatment-effects in the presence of a set of concomitant variates for the analysis of covariance (ANOCA) model relating to completely randomized layouts. The proposed procedures are shown to be conditionally distribution-free and to have some desirable large sample properties.
Madan Lal Puri. Pranab Kumar Sen. "Analysis of Covariance Based on General Rank Scores." Ann. Math. Statist. 40 (2) 610 - 618, April, 1969. https://doi.org/10.1214/aoms/1177697729