3. Judgment Sampling

Researchers, scientists, or farm managers may be called in when a crop shows a certain growing pattern or when surface differences are observed for a soil. For example, differences may occur in soil color which may be the result of many factors. The researcher judges the color differences: e.g. he may judge a particular shade of color to be typical for a sample at certain sites. Then from these sites, samples are drawn. The accuracy of these samples depends totally on the judgment of the researcher - which may or may not be good.

Some persons, in order to include as many extremes as possible, commit the error of over sampling. Probably less desirable is the person who takes the opposite approach, excluding the extremes and ending up with a sample which is not representative. In either case, the judgment of the sampler determines the accuracy of the results.

In certain situations, sample choices based on judgment are accurate enough. For example, if small sites are involved and no estimate of accuracy is needed, judgment sampling might be satisfactory. As the sample site becomes larger, and the selection of representative samples becomes more difficult and time consuming, judgment sampling is inaccurate and other sampling methods must be used.