Is there such a thing as a nonparametric regression?
The use of a ranked response in regressions has been proposed by various authors for situations where distributional assumptions such as normality of residuals, homogeneity of variance and linearity of predictor to response do not hold.
References
Conover WJ, Iman RL (1981) Rank transformations as a bridge between parametric and nonparametric statistics. The American Statistician 35(3) 124-129.
Huitema BE (1980) The ANCOVA and alternatives (1980) Chapter 12.
A technique called RGLM which minimizes the ranks of the residuals in the regression is available in MINITAB using the RREGR procedure.
McKean JW and Vidmar TJ (1994) A comparison of two ran-based methods for the analysis of linear models The American Statistician 48(3) 220-229.
Quade D (1967) Rank analysis of covariance Journal of the American Statistical Association 62 1187-1200.
Shirley EAC (1979) A distribution-free method for analysis of covariance based on tanked data. Applied Statistics 30(2) 158-162.