ABSTRACT
An effect size (ES) is simply an amount of something of interest. It can be as simple as a mean, a percentage increase, or a correlation; or it may be a standardized measure of a difference, a regression weight, or the percentage of variance accounted for. Most research questions in the social sciences are best answered by finding estimated ESs, meaning point estimates of the true ESs in the population. Grissom and Kim (2005) provided a comprehensive discussion of ESs, and ways to calculate ES estimates.
