What is the null hypothesis?

What is the null hypothesis?

• A. The predicted effect does not exist.
• B. The predicted effect exists.
• C. The null hypothesis describes data as random.
• D. Data are random.

Answer: (A)

The null hypothesis is the default claim that there is no effect or difference—the predicted effect does not exist. In hypothesis testing, you use sample data to assess whether there is enough evidence to reject this default statement in favor of an alternative hypothesis that the effect does exist. The other options misstate what the null describes: saying the effect exists corresponds to the alternative hypothesis, and describing the null or the data as random does not correctly capture the role of the null hypothesis, which is about the presence or absence of an effect, not about randomness of the data.

The null hypothesis is the default claim that there is no effect or difference—the predicted effect does not exist. In hypothesis testing, you use sample data to assess whether there is enough evidence to reject this default statement in favor of an alternative hypothesis that the effect does exist. The other options misstate what the null describes: saying the effect exists corresponds to the alternative hypothesis, and describing the null or the data as random does not correctly capture the role of the null hypothesis, which is about the presence or absence of an effect, not about randomness of the data.