Our Bayesian estimation procedure uses a modified Ewens Sampling Formula to generate posterior distributions of relative effective number and sex ratio among reproductives under gynodioecy, androdioecy, and other regular systems of inbreeding. Within a coalescence framework, those quantities depend upon the proportions of hermaphrodites and gonochores (males or females) and the rate of self-fertilization of hermaphrodites. Estimates obtained from the analysis of genetic data indicate that relative effective number is nearly but not quite maximized in three natural gynodioecious and androdioecious populations. Our evolutionary analysis indicates that the evolution of the sex ratio to the evolutionarily stable strategy (ESS) implies maximization of relative effective number if the viabilities of hermaphrodites and gonochores are identical. Accordingly, the departure of relative effective number from its maximum provides a means of inferring the relative viability of the sexes. We present posterior distribution for the relative viability of males and females relative to hermaphrodites in the populations studied.