2.5.1 Pierre Gy's Sampling Theory and the Seven Basic Sampling Errors

Gy's Seven Sampling Errors

  1. Fundamental
  2. Grouping and segregation
  3. Long-range heterogeneity
  4. Periodic heterogeneity
  5. Increment delimitation
  6. Increment extraction
  7. Sample preparation

As discussed in Section 2.3, the purpose of sampling is to obtain data of sufficient quality to support decisions that will be made about volumes of soil. To support these decisions, the sample(s) collected should represent the volume of soil, i.e., have the same types and distribution of particles, area, or volume of interest.

To achieve a representative sample, potential errors that result from collecting small volumes of material meant to represent a much larger volume need to be addressed in the design of the sampling plan. This requires an understanding of all the potential sampling errors that can bias the result. Pierre Gy describes seven basic sampling errors associated with collecting samples from particulate materials such as soil. The following sections introduce each error.

To obtain further guidance on this topic, please reference Table 2-2.