When do you reject the null hypothesis?

When do you reject the null hypothesis?

• A. If p < 0.05
• B. If p > 0.05
• C. If p = 0.5
• D. If p < 0.01

Answer: (A)

Rejecting the null hypothesis happens when the observed result is unlikely under the assumption that the null is true. This likelihood is quantified by the p-value: the probability of obtaining data as extreme or more extreme than what you saw if the null is true. The decision rule uses a pre-set significance level, typically 0.05. If the p-value is smaller than this threshold, the result is considered unlikely enough to reject the null; if it’s larger, you don’t reject. So, using the common 0.05 level, you reject when p < 0.05. A p-value greater than 0.05 does not support rejecting the null, and a p-value of 0.5 is clearly not enough evidence to reject. The option p < 0.01 would reflect a stricter criterion (alpha = 0.01) and is not the standard decision rule unless that level is specified; at the usual 0.05 level, the rule is p < 0.05.

Rejecting the null hypothesis happens when the observed result is unlikely under the assumption that the null is true. This likelihood is quantified by the p-value: the probability of obtaining data as extreme or more extreme than what you saw if the null is true. The decision rule uses a pre-set significance level, typically 0.05. If the p-value is smaller than this threshold, the result is considered unlikely enough to reject the null; if it’s larger, you don’t reject.

So, using the common 0.05 level, you reject when p < 0.05. A p-value greater than 0.05 does not support rejecting the null, and a p-value of 0.5 is clearly not enough evidence to reject. The option p < 0.01 would reflect a stricter criterion (alpha = 0.01) and is not the standard decision rule unless that level is specified; at the usual 0.05 level, the rule is p < 0.05.