Definition of Assessment Endpoints for Probabilistic Assessments

Assessment endpoints are measurable ecosystem characteristics that represent management goals (USEPA 1998). They should define 

The assessment endpoint should be not only measurable (at least potentially) but also modelable. Defining a modelable endpoint is likely to require close discussion between an assessor (who knows what they can model) and a risk manager (who knows what they want to protect). Sometimes the assessment endpoint is only indirectly related to the management goal, for example, if the assessment endpoint is a risk to individuals, but the aim is to protect population sustainability. In such cases, qualitative inference will be required to interpret the assessment result. This inference will need to be done jointly by the risk assessor and risk manager. It is likely to involve substantial uncertainty, which will have to be taken into account qualitatively when producing a narrative description of the assessment outcome. This step should be identified as part of the conceptual model. 

If the assessment is to be probabilistic, the risk assessor and risk manager should consider together how this influences the definition of the assessment endpoint. Suter (1998) suggests 5 questions for the risk assessor to ask the risk manager to help define the assessment endpoint  

1) Should any assessment endpoints be expressed as probabilities Suter (1998) points out that it can be confusing to use the term probability in defining assessment endpoints because it is unclear whether it relates to variability or uncertainty, so it will be helpful to distinguish these in the discussion with the risk manager. 

2) If effects are expressed as a threshold value, should the risk be expressed as the magnitude of exceedance, the frequency of exceedance, or the certainty of exceedance  

---