Well, the stochastic model will give a mean value and some variance, so, you would compare the range of values given by the stochastic model to the deterministic model for various times. If the deterministic value diverges appreciably from the stochastic model for any given time, then that would indicate the limits of validity for your stochastic model, or vice versa.

The results of a deterministic model can be simulated with synthetic series for example and then compared with the stochastic result. In our experience (see paper by Ratnayake and Harboe: Deterministic and stochastic optimization of a reservoir system) the stochastic model results were too optimistic and reliabilities too low.

 So, what's  the difference between VSS and EVPI? Which one is more reliable than the other to make a comparison between the results obtained by stochastic programming and deterministic solution? Thank you