Before selecting a model, the research team should have identified a specific scenario that could be informed from the application of a model. The characteristics and definition of each model’s application niche should clearly identify the suitable scenarios for future use of the model.
Application of a model to scenarios outside the bounds of its application niche is not recommended and may require an in-depth analysis of whether the model is truly appropriate for an application in the new context.
When parameterparameterA value used to numerically describe a population of values, e.g., the mean and standard deviation; or a value used to describe a dose-response curve, e.g., the intercept and the slope of a linear dose-response. calibrationcalibrationThe process of adjusting model parameters within physically defensible ranges until the resulting predictions give the best possible fit to the observed data. In some disciplines, calibration is also referred to as "parameter estimation". is specific to a modeling scenario, the subsequent application of that model outside of that scenario may result in erroneous predictions. For example, a threshold for health effects may exist at exposure levels below those covered by a particular epidemiological study. If that study is used in modeling health effects at those lower levels (and it is assumed that the level of response seen in the study holds for lower levels of exposure), then disease incidence may be overestimated (EPA, 2009b).
A Modeling Caveat
Extrapolation - is a process that uses assumptions about fundamental causes underlying the observed phenomena in order to project beyond the range of the data. In general, extrapolation is not considered a reliable process for prediction; however, there are situations where it may be necessary and useful (EPA, 2009a).
Resolution – Selection of spatial or temporal resolution (i.e., grid size) typically reflects a balance between a desired level of precision and resources required to model the system. If the resolution selected is too small, then key patterns of behavior reflected in the smaller step size may be missed altogether, or the behavior of the system may be misrepresented. (EPA, 2009b)