Checking Out Statistical Confidence Interval Critical Values

By Deborah J. Rumsey

Part of Statistics For Dummies Cheat Sheet

Critical values (z*-values) are an important component of confidence intervals (the statistical technique for estimating population parameters). The z*-value, which appears in the margin of error formula, measures the number of standard errors to be added and subtracted in order to achieve your desired confidence level (the percentage confidence you want). The following table shows common confidence levels and their corresponding z*-values.

Confidence Level z*– value
80% 1.28
85% 1.44
90% 1.64
95% 1.96
98% 2.33
99% 2.58