2. The method of claim 1 , wherein selecting a subset of the modeled impairment correlation terms comprises selecting the modeled impairment correlation terms having corresponding model fitting parameters that satisfy a threshold.
2. The method of claim 1 , wherein selecting a subset of the modeled impairment correlation terms comprises selecting the modeled impairment correlation terms having corresponding model fitting parameters that satisfy a threshold. 4. The method of claim 2 , wherein the threshold is particular to individual groups of one or more of the modeled impairment correlation terms.