Statistical Significance = a measure of how well a sample represents the overall population
Effect Sizes (fractions of Std. deviation based of reference group) = human scales of differences in data. E.G. 3/4 of a Std. Deviation
So the Effect Size of the data in a sample tells us in human terms how much of a difference there is between the denominations, and the Statistical Significant tells us to what degree that difference is representative of the whole population.