The effect is the difference between the true population parameter and the null hypothesis value. Effect is also known as population effect or the difference. For example, the mean difference between the health outcome for a treatment group and a control group is the effect.
The true population parameter is not known. Consequently, samples are taken and a statistical test, such as a t-test or a one-way ANOVA, determines whether an effect exists and estimates its size.« Back to Glossary Index