Transferring results from other studies

The text on this page is taken from an equivalent page of the IEHIAS-project.

There is clearly little to be gained by repeating work that has already been done. Previous studies are thus a rich and useful source of information when designing assessments, and often provide good indications of the likely range and level of impacts. In most cases they should therefore be the first port of call when undertaking screening for a new assessment.

Using results from other studies nevertheless has to be done with care, for differences in the context or design of the assessment can mean that they do not always provide a reliable analogue. Of course, not every element of a study has to match to make its results useful: for example, a previous assessment can provide important information on how exposures may change under a given scenario, even if the health outcomes being considered are different. The crucial thing in each case, however, is that earlier links in the causal chain have been defined and analysed in a comparable way. Thus, we cannot directly transfer results on health outcomes from a previous study if the exposures are not directly analagous to those we wish to assess; nor can we use information on changes in exposure if the populations and emission scenarios are not comparable.

The first, and most important, step in determining whether other studies can provide useful information is thus to examine the conceptual framework on which it was based, and identify elements of similarity. Not all studies will have undertaken an explicit issue-framing process, and even those that have done so may not present the results in an explicit way; a conceptual model for the previous study may thus have to be reconstructed from the available information, or by consultation with those involved. In making these comparisons, crucial elements to focus on are:

1. The scenarios - were the scenarios on which the assessment was based comparable in terms of their assumptions and expectations?
2. Context - was the assessment undertaken within a similar environmental, demographic and socio-economic framework?
3. Scale - was the assessment conducted at a comparable geographic and time scale?
4. Causal factors and processes - were the causal factors and processes (e.g. sources, contaminants, exposure pathways) comparable both in terms of their definition and the way they were assessed (e.g. measurement units)?
5. Impacts - were the impacts being assessed directly comparable in terms both of the health effects and the population groups concerned?

Reviewing previous studies, and determining their relevance, can be a somewhat subjective process. To minimise this subjectivity, therefore, it is helpful to ensure that the review is conducted according to a set of predefined rules. The methodology for systematic review used to derive exposure-response functions provides clear guidance. Likewise, it is often useful to involve a panel of experts in the process, in order to provide deeper insight and balance in the review; gudance is given via the link to expert estimation methods.

Access to a range of previous integrated assessments studies is available via the Examples in the Toolkit section of this Toolbox