The steps involved may vary, depending on the nature of the issue, the scenarios and the type of assessment.  In broad terms, however, the process follows the causal chain.  It thus comprises four main steps:

1. Estimating exposures of the target population to the hazards of concern
2. Selecting an appropriate exposure-response function
3. Quantifying the health effects
4. Aggregating the health effects into a set of synoptic indicators of impact

Because assessments involve a comparison between two or more scenarios, however, each of these steps has to be repeated, for each of the scenarios.  Ensuring that this process is done consistently is crucial, for otherwise biases in the results are likely to occur.   It is therefore essential that the assessment protocol is carefully and closely followed throughout the execution phase.