Sampling judgmental

A sampling plan that combines judgmental sampling with systematic sampling. 

Systematic—Judgmental Sampling Combinations of the three primary approaches to sampling are also possible. One such combination is systematic-judgmental sampling, which is encountered in environmental studies when a spatial or tempo-... 

Systematic-judgmental sampling scheme for monitoring the leaching of pollutants from a landfill. Sites where samples are collected are represented by the solid dots. 

Contrary to probabilistic sampling, judgmental sampling is intentionally non-random and even biased. Data obtained through judgmental sampling cannot be statistically evaluated. 

Judgmental sampling is used to obtain information about specific areas suspected of contamination. The sampling point selection is based on the existing information on the contamination source and history. Typically, an individual who has the detailed knowledge of the area to be sampled makes decisions on the sampling point placement. 

This type of sampling may also rely on immediate observations. For example, judgmental sampling is appropriate for investigating hot spots, such as stains, spills, or discoloration, which may indicate contamination. The knowledge of the operational modes or past practices at the project site may also serve as a basis for judgmental sampling. 

The regulated UST pit and pipeline sampling is judgmental sampling. The selection of sampling points is biased towards the most probable sources of leaks, such as the... 

Combinations of any two are also used. The judgmental sampling pattern requires the smallest number of samples but the relative bias is the largest the opposite holds for the random pattern, where the bias is the smallest but the number of samples is the largest. In scientific studies it is the judgmental approach that is most often applied, whereas for legal purposes absolutely random sampling is often needed. 

This presentation provides an overview of sampling methods and tools suitable to address most site characterizations. The basic sampling types discussed are the systematic, random, and judgmental sampling approaches. 

Figure 2.5 Judgmental sampling. The placement of the tanks may have been recorded in documentary sources (e.g., from the initial site assessment). The zone sampled is only that around the known area.

A selective sample is one which has been chosen to demonstrate a particular aspect of the material from which it is taken, e.g. a sample of water taken from immediately downstream of an industrial outfall to assess the worst possible situation with regard to potential pollution. Some analysts refer to judgmental samples as those chosen to illustrate a particular property of the material under consideration. 

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