The document discusses the null hypothesis for a single linear regression model. It explains that a null hypothesis states that there is no effect or relationship between the independent and dependent variables. For a regression predicting ACT scores from hours of sleep, the null hypothesis would be: "There will be no significant prediction of ACT scores by hours of sleep." The document provides a template for writing the null hypothesis and works through an example applying the template to the relationship between hours of sleep and ACT scores.