Cohen’s d is a statistical measure that quantifies the standardized difference between two means. In simpler terms, it helps assess the size of the difference between two groups by expressing it in standard deviation units. A larger Cohen’s d indicates a more substantial difference between the groups being compared. It serves as a metric for gauging the standardized distinction between two means. In the examination of age distribution among individuals fatally shot by the police, Cohen’s d was employed to evaluate the effect size pertaining to the age gap between black and white victims.

To compute Cohen’s d, the variance between the means (specifically, the mean ages of white and black individuals killed by police) is divided by the pooled standard deviation of both groups. The pooled standard deviation, a weighted average adjusted for sample sizes, accounts for the standard deviations of both groups. In the given dataset, the computed Cohen’s d stood at 0.577485, signifying a medium effect size according to Cohen-Salkowski guidelines. This implies that the 7.3-year average age difference between white and black individuals killed by police is of moderate magnitude, suggesting a statistically significant yet intermediary impact—not large or small, but falling in between. The resulting Cohen’s d value provides a standardized measure of effect size, helping to interpret the magnitude of the difference between the means of the two groups.