The empirical rule states that almost all observed data for a normal distribution will fall within three standard deviations of the mean or average. What Is the Empirical Rule? The empirical rule ...

Using the empirical rule, for example, if 100 test scores are collected and used in a normal probability distribution, 68% of those test scores should fall within one standard deviation above or ...

Another use of lowercase sigma is in the Empirical Rule, which describes the distribution of data in a normal distribution.