Why is effect size important?
Effect size is important because it provides information about the size or magnitude of the effect. Effect size can help us assess change and understand the practical significance/importance of a treatment. If, for example, students in a school district who attend a math tutoring program are found to do better on a standardized math test than students who did not attend the tutoring program, decision makers in the school district will want to know “how much better?”. If the students who received tutoring did only marginally better, administrators may not implement a district-wide tutoring program for math. However, if the effect size of the tutoring program is large, administrators will have to consider how to implement the program for all students. This example demonstrates the practical importance of effect size. Statistical significance is not enough when considering the relationship between two populations; effect size helps us understand the real importance of the relationship bet
