Estimating EPCs for Composite and Discrete Sampling Results

You might have a site-specific dataset that contains composite and discrete sampling results. For example, composite samples may be collected across a large residential property to evaluate average concentrations. Discrete samples may be collected from certain areas that the property owner believes are unique relative to the remainder of the property (e.g., play areas, hotspots, the center of a soccer field with barren soil).

It is not appropriate to combine these results into a single data set.

In this case, it is not statistically appropriate to combine results collected from the two methods into a single dataset. This would weight discrete samples more heavily in the dataset. The resulting concentration might be biased toward the average of the discrete samples. Health assessors may, however, gain valuable insight by evaluating the magnitude of difference between composite and discrete sampling data. If you need assistance on this topic, contact an ATSDR statistician.