How to Calculate Percentages Within Two Standard Deviations

According to the "Principles of Statistics" by M.G. Blumer, standard deviation is, "a widely used measure of the variability or dispersion, being algebraically more tractable though practically less robust than the expected deviation or average absolute deviation." In other words, standard deviation is used to account for the naturally occurring deviations in populations.

Things You'll Need

• Calculator

Instructions

1. Find the average of the population's values by adding the data and dividing by its total number.

2. Compute the difference of each value from the mean and square the result.

3. Divide the sum of the answers from step two by the total number and take the square root. If the answer is less than or equal to two, then the percentages are within two standard deviations.

References

• "Principles of Statistics"; M.G. Bulmer, 1979.