But, if the policy question to be addressed is a longer-term strategic issue, where there is a strong need to understand interactions among individuals; to assess dynamic risks; or to evaluate the epidemiological transition of a population; in this case, microsimulation may be a preferred method (Anderson et al. Finally, if the policy question refers to the impact of health expenditure in a very short run (e.g. up to two years), then macro-level models would probably be the first choice. The remainder of this section presents the main features of each class of health forecasting models.