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Highlights Female mice do not show more overall variance in temperature or activity than do males. When measuring rodents, phase of the daily rhythm accounts for a substantial amount of the overall variance. Female mice show less unstructured variance than do male mice, and for both sexes, time of day is the biggest influence on structured variance, with estrous cycle variance accounting for as little as 3% overall. Many analytic approaches allow for quantification of similarity or predictability in biological time series data, and should be adopted more broadly to improve measurement precision for subjects of any sex. Sex differences exist in mean, variance, variance composition, and rhythm composition for most measures. The evidence presented here that female subjects are less variable overall than males should encourage inclusion of Sex as a Biological Variable in preference to only including one sex in a study.