Normal Distribution

Normal distributions are sampling distributions generated when an attribute possessing a continuous, and typically unbounded, range of outcomes is recorded from a series of sample units. Sample units should be independent and selected by random sampling. Normal distributions follow a symmetrical form, characterized as a bell-shaped curve.

Normal distributions are observed in many biological populations, wherever most individuals represent a fairly average expression of the continuous attribute such as plant height or weight. In rangeland sampling, biomass data generally follows a normal distribution. Data for other attributes, such as cover and density, will also tend toward a normal distribution by selecting an appropriate sample unit size or calculating the parameter from a group of sample units.

Sample data following a normal distribution are analyzed using conventional inferential statistical procedures, which are founded on established relationships between sample statistics and population parameters.

References and Further Reading

Bonham, C.D. 1989. Measurements for terrestrial vegetation. John Wiley Sons, New York, NY. pp 59-65.

Dowdy, S. and S. Weardon. 1991. Statistics for research. John Wiley Sons, New York, NY. 2nd ed. pp 161-191.