Exposure response functions (ERF) describe quantitatively how much a certain health effect increases when the exposure of a certain stressor increases.  The ERF needs to relate specifically to the exposure metric and health endpoint used in the assessment. 

The ERF can be derived in a number of ways. Where a published and up-to-date ERF is available from an authoritative organisation, such as the World Health Organization, this should preferably be used.  If not, a systematic review (including if appropriate a meta-analysis) should ideally be conducted to derive an ERF for the key impact pathways.  Where this, too, is not possible, an alternative is to make use of the formal methods of an expert panel. Systematic reviews and expert panels are both time-consuming to design and run, so modified, less-time consuming versions may be more appropriate. Options include:

• adopting the ERF used in previous HIAs;
• taking results from an already published and good-quality meta-analysis;
• using results from a key multi-centre study.

If these informal methods are used it is advisable to consult expert(s) in the relevant policy field (not a formal expert panel). 

These methods can be applied to animal and human studies. However, if applied to animal studies, extrapolation to humans is necessary. In this case, a qualitative assessment should first be carried out to evaluate whether an observed effect in animal studies applies to humans.  

A protocol, giving guidelines on how to develop ERFs, is available via the link under See also, below.  Figure 1 (below) provides a summery of this protocol and presents a checklist of questions that should be considered in order to derive an ERF.

An ERF data set, providing suggested exposure-response functions for common exposures and health endpoints is also included in the Data section of the Toolkit. 

Figure 1. A checklist for deriving an ERF