An advantage of the equivalent circuit model approach is in representing manufacturing tolerance. Results from a Monte Carlo simulation using Gaussian distributions about the nominal part values are shown in Figure 1.
In the simulator, the standard deviations for the inductors and capacitors were specified at +/- 1.66% and +/- 5%, respectively. Over 30 simulation trials, the extreme capacitance values obtained were 86% and 114% of the nominal value, or about three standard deviations. This is a typical result, and is the reason why the specified standard deviation in a simulator should be ~33% of the vendor-specified tolerance if the part value spread is assumed to be Gaussian.