distribution, bell-shaped, can be used
If a distribution is roughly bell shaped, then
approximately 68% of the data will lie
within 1 standard deviation of the mean. That is, approximately 68% of the data will lie between μ−1σ and μ+1σ.
Approximately 95% of the data will lie
within 2 standard deviations of the mean. That is, approximately 95% of the data will lie between μ−2σ and μ+2σ.
Approximately 99.7% of the data will lie
within 3 standard deviations of the mean. That is, approximately 99.7% of the data will lie between μ−3σ andμ+3σ.
The Empirical Rule can also be used on sample data with
in place of μ and s in place of σ.