Confidence Interval

An estimated range of values which is likely to include an unknown population parameter. The 95% (p-value = .05) and 99% (p-value = .01) confidence intervals are the most commonly used.

If an estimated annual percentage change (APC) is -2.44 with a 95% confidence interval of (-2.83, -2.05), then we are 95% confident that the actual APC is between a decrease of -2.83% and a decrease of 2.05%. Inversely, there is still a 5% chance that the actual APC is not in the confidence interval (between the upper and lower confidence limits).