What does the null hypothesis state?

The null hypothesis posits that there is no relationship or effect between two variables. This foundational concept in statistics serves as a default position that suggests any observed differences or relationships in the data can be attributed to chance rather than a true effect.

In hypothesis testing, researchers typically aim to either reject the null hypothesis or fail to reject it based on the evidence collected from their experiments or observations. By assuming the null hypothesis at the start, researchers can then use statistical methods to assess whether the data provides sufficient evidence to support an alternative hypothesis, which usually suggests that there is a significant effect or relationship present.

Other choices imply a presence of a relationship or an effect, which contradicts the null hypothesis's core assertion. For example, claiming there is a strong correlation, a positive outcome from a treatment, or that variables significantly affect one another all infer that some kind of relationship exists, thus making those assertions incompatible with the fundamental premise of the null hypothesis.