If a 95% CI for relative risk includes 1, what does this imply about statistical significance at the 0.05 level?

• A. The result is statistically significant
• B. The result is not statistically significant at the 0.05 level
• C. The null hypothesis is true
• D. The study has perfect precision

Answer: (D)

The main idea is that the null value for relative risk is 1, meaning no association. If a 95% confidence interval for the relative risk includes 1, the data are compatible with no effect, so you cannot reject the null at the 0.05 level. In other words, there isn’t enough evidence to claim a statistically significant association. This doesn’t prove the null is true; it just reflects insufficient evidence to conclude a real effect. It also isn’t about perfect precision—the interval’s width reflects precision, and including 1 can happen even with reasonably precise estimates. Significance would be shown if the entire interval were above 1 or entirely below 1.