Confidence interval (CI)

A 95% confidence interval (CI for short) is a plausible range around an estimated value. The method is built so that, over many repetitions of a study, such ranges contain the true value in about 95 of 100 cases.

Example: Difference 6.8 points, 95% CI [2.1, 11.5]. With these data, true differences between about 2 and 11.5 points are plausible.

Caution: A narrow range means a precise estimate. If the range for a difference includes 0, "no difference" is also consistent with the data.