•If the
population is normally distributed, you can estimate the percentage of the population within
1, 2, and 3 standard deviations of the mean:
•68% of
cases lie +/- 1 s.d. of mean
•95% of
cases lie +/- 2 s.d.’s of mean
•99.9%
of cases lie +/- 3 s.d.’s of mean