Parametric Tolerance Limit
Parametric Tolerance Limit
See Also:
Non-Parametric Tolerance Limit
Confidence Interval MCL Comparison
Description:
A tolerance limit establishes a concentration range that is constructed to contain a specified proportion of the population with a specified confidence coefficient. The parametric tolerance limit can be implemented two ways:
1. Comparison to Statistic -- The tolerance limit can be constructed from background data and each compliance well sample compared to the tolerance limit. If the compliance well sample exceeds the tolerance limit, the sample shows statistical evidence of contamination.
2. Comparison to MCL -- A separate tolerance limit can be constructed from data for each compliance well, and the tolerance limit compared to a compliance limit (MCL or action limit) for that parameter. If the tolerance limit value exceeds the compliance limit, the well is shown to be contaminated.
As few as 3 measurements can be used to construct a tolerance limit. Data should have equal variance and follow a normal distribution.
Use:
To compare each individual compliance well sample to a tolerance limit constructed from background well data, or to compare compliance well data to a compliance limit.
Remarks:
The USEPA 1989 and 1992 Guidance documents differ in the method of calculating the tolerance factor. Each provides slightly different results. ChemStat provides a choice of the two methods. From Select | Parametric Tolerance Interval, or from the tolerance interval right-click context menu, select either 1989 Calculations, or 1992 Calculations.