Sample Variance

The sample variance (s2) is a measure of dispersal that reflects the spread of data around the sample mean. The sample variance is calculated as

s-squared = sum ((x - x-bar)squared) / (n - 1)

This equation indicates that the variance gives us a measure of dispersal by considering the average absolute difference between each value in the data set and the sample mean.

We rarely have the need to directly calculate the population variance (greek letter sigma2), because it is unusual to measure all members of the population. However, we can estimate the population variance from our sample data, from the assumption that

greek letter sigma2 = s2

References and Further Reading

Bonham, C.D. 1989. Measurements for terrestrial vegetation. John Wiley Son, New York, NY. pp 54-58.

Cook, C.W., and J. Stubbendieck. (eds). 1986. Range research: Basic problems and techniques. Society for Range Management, Denver, CO. pp 217-219.