The null hypothesis is one of two mutually exclusive hypotheses in a hypothesis test. The null hypothesis states that a population parameter equals a specified value. If your sample contains sufficient evidence, you can reject the null hypothesis and conclude that the effect is statistically significant. The null hypothesis is often displayed as H0.
In every experiment, there is an effect or difference between groups that the researchers are testing. It could be the effectiveness of a new drug, building material, or other intervention that has benefits. Typically, the null hypothesis states that the true effect size equals zero—that there is no difference between the groups. Therefore, if you can reject the null hypothesis, you can favor the alternative hypothesis, which states that the effect exists (doesn’t equal zero) at the population level.« Back to Glossary Index