BS ISO 5667-20:2008

Foreword
Introduction
1 Scope
2 Summary of key points
3 Types of error and variation
  3.1 General
  3.2 Analytical error
  3.3 Overall uncertainty
4 Activities
  4.1 Estimation of summary statistics
  4.2 Thresholds for water quality and compliance
  4.3 Confidence of failure
  4.4 Methods for thresholds expressed as percentiles
  4.5 Non-parametric methods
  4.6 Look-up tables
5 Definition of thresholds
  5.1 General
  5.2 Ideal thresholds
  5.3 Absolute limits
  5.4 Percentage of failed samples
  5.5 Calculating limits for effluent discharges
6 Declaring that a substance has been detected
7 Detecting change
8 Classification
  8.1 General
  8.2 Confidence that class has changed
Annex A (informative) Calculation of confidence limits
Annex B (informative) Calculation for the binomial distribution
Annex C (informative) Sample results with high error or reported
                      as less than a limit of detection
Bibliography

Provides principles, basic requirements, and illustrative methods for dealing with the use of sample data for decision making based on the assessment of the confidence that water quality: meets targets and complies with thresholds; has changed; and/or lies in a particular grade in a classification system.

This part of ISO5667 establishes principles, basic requirements, and illustrative methods for dealing with the use of sample data for decision making based on the assessment of the confidence that water quality: meets targets and complies with thresholds; has changed; and/or lies in a particular grade in a classification system. This part of ISO5667 also specifies methods for preliminary examination of the sensitivity of decisions to error and uncertainty, although it does not cover the full range of statistical techniques. This part of ISO5667 provides general advice on decision making related to constraint formulation for expression of thresholds and targets and the form and scale of sampling programmes. NOTE1 In the water industry, “standard” is commonly used to indicate the value or limit of a parameter of interest. However, in this part of ISO5667, the term “threshold” is used to avoid confusion with published national, regional, and International Standards. NOTE2 This document is framed in terms of sampling and measurement of chemical concentrations, in particular those subject to strong day-to-day temporal variations. The principles apply, however, to any item estimated by sampling which is subject to random error, including microbiological and biological data, and data subject to strong spatial variations.