Fig 2. Representation of the trade off between tractability and realism in model construction.

Models are positioned along the axis based on the relative complexity of the model, as determined by the number of state variables (the dimensionality) and model structure (the interactions between state variables). The nonseasonal SEIR model is the simplest model, with the FRED and Mplex models being the most complex. Simpler models lend themselves to mathematical analysis, while sacrificing realism. More complex models better represent reality, at the expense of analytical tractability.