Assessments of environmental health issues are often complex, and can produce a large array of information – far beyond what many users will need or be able to cope with.   For most users, therefore, a more limited set of synoptic information is required, which captures the most important elements of the assessment.  These are provided by indicators.

The way in which indicators are selected and defined is vital, for they are the main results from the assessment: what the indicators tell us is what we learn from the assessment, and what is not covered by an indicator might as well not be assessed.

At the same time, it is important to remember that many different stakeholders may have interests in the assessment, and their interests may not all be the same.  Different stakeholders may therefore wish to emphasise different aspects of the assessment, and thus demand different indicators.

For this reason, it is important wherever possible to involve stakeholders in the process of selecting indicators.

Indicators can thus take many different forms, and serve different purposes for the stakeholders concerned.  Pressures also often occur to apply a large number of indicators, in the attempt to capture every aspect of the assessment and satisfy every interest.  This can, of course, be dangerous, for it leads to difficulties in bringing together the results of the assessment, and agreeing on what conclusions to draw.

To ensure that the indicators do justice to the assessment, and meet the needs of users, they need to be selected and constructed with great care.  Clear and strict (and agreed) criteria need to be established and agreed at the start; thought and honesty need to be applied in ensuring that the indicators meet these criteria.   Ideally, also, the indicators should be tested before they are used, in order to make sure that they are valid and work effectively.