Univariate Estimates of Sexual Dimorphism: The Effects of Intrasexual Variability ELISABETTA MARINI, 1 * WALTER RACUGNO, 2 AND SILVANA M. BORGOGNINI TARLI 3 1 Sezione di Scienze Antropologiche, Dipartimento Biologia Sperimentale, Universita ` di Cagliari, Cittadella Universitaria di Monserrato, 09042 Monserrato, (Cagliari), Italy 2 Dipartimento di Matematica, Universita ` di Cagliari, 09124 Cagliari, Italy 3 Sezione di Antropologia, Dipartimento di Etologia, Ecologia, Evoluzione, Universita ` di Pisa, 56126 Pisa, Italy KEY WORDS dimorphism variations; methods; statistical indices ABSTRACT The difference between male and female values of quantita- tive traits depends on the distribution of the variables within each sex, increasing with the rise in the difference between male and female average values and with the decrease of the dispersion of measurements in both sexes. This paper deals with the sensitivity of some widely used indices (relative difference between male and female mean values (MDI), Student’s t, and the so-called Bennett-Chakraborty-Majumder D coefficient) with respect to intra- sexual variability. The Kolmogorov-Smirnov distance (KS) is suggested here as a further index of dimorphism, although it is not usually utilized for this purpose. The theoretical approach is accompanied by the analysis of empirical data (metric variables obtained from a sample of present Sardinians) and by computer simulations under various assumptions. Indices based on the difference between male and female average values are not able to evaluate fully the various aspects of dimorphism. Student’s t proved to be an adequate measure of whole sex differences, both in real and in simulated samples, as intrasexual variability is included in its formulation. The D index also proved to be a good measure of undivided sexual dimorphism, as it is the result of formal examination, and from application to empirical or to simulated cases. The Kolmogorov-Smirnov distance gave the best performance both in formal examination and in the whole simulation results, as it takes into account intrasexual variability, and is applicable to any kind of distribution. In simulated cases it was sensitive to variations of means and variances, and it was able to evaluate variance dimorphism. Since the last three indices measure the combined effect of size and variance dimorphism, the joint use of the MDI index is suggested in order to isolate the relative contribution of the difference between the means. Am J Phys Anthropol 109:501–508, 1999.  1999 Wiley-Liss, Inc. In the study of sexual dimorphism, intra- sexual variability has only recently received some consideration (Meindl et al., 1985; Tague, 1989, 1991, 1992, 1995; LaVelle, 1993, 1995; Plavcan, 1994), in spite of the fact that such variability influences the manifesta- tion of dimorphism and its interpretation. Grant sponsor: M.U.R.S.T. 60%. *Correspondence to: Elisabetta Marini, Sezione di Scienze Antropologiche, Dipartimento Biologia Sperimentale, Universita ` di Cagliari, Cittadella Universitaria di Monserrato, SS 554, Km 4500, 09042 Monserrato (Cagliari), Italy. E-mail: emarini@unica.it Received 20 March 1997; accepted 2 April 1999. AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 109:501–508 (1999)  1999 WILEY-LISS, INC.