The main model parametrization methods are the method of least squares,the method of maximal likelihood, and Bayesian methods. There are other statistical challenges when parametrizing models, for example, under-reporting.Not all infected individuals are officially counted. For example,most people who have the flu suffer at home and do not visit a doctor and
have their diagnosis confirmed by a laboratory. One needs to estimate theunderreporting rate. At the beginning of the 2009 H1N1 flu pandemic theunder-reporting rate in the U.S. was estimated to be about 80 to 1 ([13]).