Comparison of the observed absolute-magnitude-dependent SMC OBe star fraction with theory. At the top of each panel we show indicative masses, as in Fig. 3. Top: OBe star fraction in a theoretical single star population, for which we explore three different minimum v/v_crit values that stars require to manifest themselves as OBe stars, with v/v_crit being the fraction of the critical rotation velocity. Bottom: OBe star fraction in theoretical binary populations. With blue and orange lines, we show theoretical predictions derived from ComBinE simulations, for different combinations of the mass transfer efficiency β and binary fraction f_bin. In the theoretical populations, single stars are assumed to not contribute to producing OBe stars. For each theoretical binary population, we assume that all stars with v/v_crit > 0.7 are OBe stars. In the Appendix, we provide a similar figure, but where v/v_crit > 0.8 and v/v_crit > 0.9 are set as the required rotation velocities for OBe stars in the binary populations (Fig. C.1).