In experiments, psychologists use inferential statistics to test the null hypothesis. The null hypothesis states that the independent variable has no effect on the dependent variable. It asserts that the groups being compared represent the same population and do not differ significantly from one another. If the researcher has a specific hypothesis about the way in which the independent variable will affect the groups, a directional hypothesis is used. If the researcher does not have a specific hypothesis about the effects of the independent variable but simply claims that it will change the dependent measure, a non-directional hypothesis is used.