Systematic-judgmental 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. 

A sampling plan that combines judgmental sampling with systematic sampling. 

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. 

Accuracy is the distance of a measured or estimated value to its true value. Inaccuracies (systematic deviations or bias) may arise from inadequate survey design and processing of the samples. Expert judgment is needed to assess the accuracy however, that implies that the origin and the extraction of the data is described (sampling design and conditions). 

Control charts are used in many different applications besides analytical measurements. For example, in a manufacturing process, the control limits are often based on product quality. In analytical measurements, the control limits can be established based on the analyst s judgment and the experimental results. A common approach is to use the mean of select measurements as the centerline, and then a multiple of the standard deviation is used to set the control limits. Control charts often plot regularly scheduled analysis of a standard reference material or an audit sample. These are then tracked to see if there is a trend or a systematic deviation from the center-line. 

Frequently, judgment combined with systematic or random sampling is used to take the advantages from each (Fig. 2.6). Table 2.1 summarizes the advantages and... 

Assessment of the sampling pattern (i.e., random, systematic, or judgmental) Statistical evaluation of distribution parameters of the elements of interest Implementation of quality measures for the assurance of data quality Incorporation of a special depth function for element distribution, particularly for urban soils... 

The final step is integration of the sample lanes and comparison of the calculated variance with the variance of the standards. The difference is often noticeable. If it has a characteristic trend, it is the result of systematic error. The chromatographers must use his e own judgment to evaluate bias separately. If the distribution is perfectly random, the reason for the difference is hidden in the consistency of samples and standards applied. It may have a negative or positive value ... 

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