When is the confidence interval not statistically significant?

When is the confidence interval not statistically significant?

• A. When it contains 0
• B. When it is very narrow
• C. When it is entirely above zero
• D. When it is symmetrical

Answer: (A)

A confidence interval shows the range of values that are compatible with the data at a given level of confidence. Statistical significance hinges on whether the null value is plausible within that range. For many studies, the null value is zero (no effect). If zero lies inside the interval, you can’t rule out no effect based on the data, so the result isn’t statistically significant at the chosen alpha level. That’s why including zero means the effect is not significant. Width and symmetry aren’t by themselves about significance. A very narrow interval means more precision, but it can still include zero and be non-significant. Conversely, an interval entirely above zero (or entirely below zero) excludes zero and would be considered statistically significant. So the key idea is whether the null value is contained in the interval.

A confidence interval shows the range of values that are compatible with the data at a given level of confidence. Statistical significance hinges on whether the null value is plausible within that range. For many studies, the null value is zero (no effect). If zero lies inside the interval, you can’t rule out no effect based on the data, so the result isn’t statistically significant at the chosen alpha level. That’s why including zero means the effect is not significant.

Width and symmetry aren’t by themselves about significance. A very narrow interval means more precision, but it can still include zero and be non-significant. Conversely, an interval entirely above zero (or entirely below zero) excludes zero and would be considered statistically significant. So the key idea is whether the null value is contained in the interval.