This guide establishes important principles for dealing with the use of sample data for decision-making. The scope includes decisions based on the assessment of the confidence that water quality:. meets targets and complies with thresholds. has changed. lies in a particular grade in a classification system.This guide sets out basic requirements and illustrative methods that will be adequate in many decisions of this type and in 3.1 and 3.3. In other cases these methods will also serve as a preliminary look at the sensitivity of decisions to error. This guide does not cover the full range of statistical techniques.The discipline of taking such decisions shou