I'm optimizing 5 parameters for an option pricing model. Now I want to asses whether these parameters are stable over time (i.e., a year). For this I create about 12 subsamples and estimate the optimal parameters for each subsample (I do this by minimizing a cost function, i.e., chi-squared, under a certain threshold).
Now I'm not really sure what statistic quantifies those estimated parameters as stable. Is it a low standard deviation? What would be the best way to prove those parameters are stable over time?
EDIT: The model which I'm using is neither differentiable nor is it continuous.
Related question, without an answer: How to test stability/variability of statistic over time, using R