Dear Dynare users,
my question is the following: what is the difference between theoretical moments that are displayed in the Command window and moments that are calculated as follows:

First, shocks are randomly generated from normal distribution with mean zero and standard deviation set equal to the posterior mean
eps_epsilon = [normrnd(0,oo_.posterior_mean.shocks_std.epsilon_epsilon,[1 400])]’;
etc…
In the end I have ex_=[eps_epsilon and other shocks…] 
Time series are then simulated as:
Z=simult_(ss,dr,ex_,iorder);
This is repeated, for example, 10.000 times.
Then I calculate the standard deviation of time series which I’m interested in. Finally, I calculate the average standard deviation over the 10.000 samples.
Thank you for your answer.