Mayer and Robinson's M: Mayer, L. S., and Robinson, J. A. Measures of association for multiple regression models with ordinal predictor variables. In Sociological Methodology 1978, edited by K. F. Schuessler. San Francisco: JosseyBass, 1977.
Fisher's Z transformation: Mayer, L. S., and Robinson, J. A. Measures of association for multiple regression models with ordinal predictor variables. In Sociological Methodology 1978, edited by K. F. Schuessler. San Francisco: JosseyBass, 1977. ; Hays, W. L. Statistics for the Social Sciences. Second edition. New York: Holt, Rinehart, and Winston, 1973. p. 662