What is a 95 percent confidence interval?

A 95 percent confidence interval is a range in which it is estimated that 95 percent of all future data will fall. The size of the range gives information about the precision of measurements and the certainty of the data.

Larger 95 percent confidence interval ranges mean there is more uncertainty in the data. If the 95 percent confidence interval to predict the age of retirement for Alice is 55 to 70, then there is only a 5 percent chance that Alice will retire before 55 or after 70. However, in a country where nearly everyone retires at the age of 66, the 95 percent confidence interval for Alice's retirement age would be much narrower to show less uncertainty.