Simulations build on the paper Phillips et al. (2023) Statistical simulations show that scientists need not increase overall sample size by default when including both sexes in in vivo studies. PLoS Biol 21(6) 3002129 here. The aim is to show that heteroscedasticity in the (nuissance) variable in a model testing for some treatment-of-interest effect does indeed lead to drops in power and mandates increased sample size (often as much as twofold increse).