\(h^2_{l}\), proportion of variance in liability explained by the predictor:

Via equation 15 of Lee et al. (see citation) convert Nagelkerke's R2 to an R2 in liability at the population level.

Lee SH, Goddard ME, Wray NR, Visscher PM. (2012) A better coefficient of determination for genetic profile analysis. Genet Epidemiol. 2012 Apr