Effect size represents the degree to which two populations do not overlap. the less that two populations overlap, the larger the effect size will be. effect size for the t test for independent means is the difference between the population means divided by the standard deviation of the population of individuals. since the population means and population standard deviation are ▼ unknown, known, estimate them using the ▼ population mean sample means and the ▼ pooled sample standard deviation. the larger sample standard deviation. population standard deviation. the estimated effect size of this study is ▼ medium. large. small.