Which statement best describes null and alternative hypotheses and the role of the null in hypothesis testing?

Which statement best describes null and alternative hypotheses and the role of the null in hypothesis testing?

• A. The null hypothesis predicts an effect but not its direction.
• B. The null hypothesis is used only in descriptive studies.
• C. The null hypothesis assumes no effect; alternative posits effect; hypothesis testing assesses evidence against null.
• D. The null hypothesis is always true.

Answer: (C)

In hypothesis testing, you start with a null hypothesis that typically states no effect or no difference, and an alternative hypothesis that there is an effect or difference. The test uses the data to decide whether there is enough evidence to cast doubt on the null. If the data show a small probability of obtaining such results assuming the null is true (a low p-value) at your chosen level of significance, you reject the null in favor of the alternative; otherwise you do not reject it. This captures the basic idea: the null assumes no effect, the alternative posits an effect, and hypothesis testing evaluates evidence against the null. The other statements misstate aspects: the null does not predict an effect, hypothesis testing is not limited to descriptive studies, and the null is not always true—it’s a provisional claim tested against the data.

In hypothesis testing, you start with a null hypothesis that typically states no effect or no difference, and an alternative hypothesis that there is an effect or difference. The test uses the data to decide whether there is enough evidence to cast doubt on the null. If the data show a small probability of obtaining such results assuming the null is true (a low p-value) at your chosen level of significance, you reject the null in favor of the alternative; otherwise you do not reject it. This captures the basic idea: the null assumes no effect, the alternative posits an effect, and hypothesis testing evaluates evidence against the null. The other statements misstate aspects: the null does not predict an effect, hypothesis testing is not limited to descriptive studies, and the null is not always true—it’s a provisional claim tested against the data.