This study investigated the differences in relative improvement in personal best competition times among collegiate track and field endurance runners between sex and level of competition. The researchers analyzed competition results from over 90 athletes who qualified for NCAA National Championships in a middle- or long-distance event and competed for the same college team over 4 years. They found that Division I athletes and female athletes improved more on average over their careers compared to Division III and male athletes, respectively. However, the interaction between sex and division was only marginally significant, suggesting males may improve more in Division III than Division I, while females improve more in Division I than Division III.