# Distribution of realized volatility for stock prices from a GBM

If you generate random stock price paths according to a GBM with daily increments, what will be the distribution of the realized volatility? Assume that the realized volatility is measured over daily increments for the whole year.

I assume that the realized volatility is an unbiased estimator of the parameter sigma in the GBM, but I've never seen it proved. As for the higher moments, what can be said ?

• Is GBM stands for Generalized Brownian Motion and you assume that $\sigma$ is not constant? May 2 '17 at 12:27
• The realized variance will have a Chi-Squared distribution, centered around the (constant) true variance used in the MonteCarlo simulation. A realized variance calculated from N non-overlapping observations will be Chi-Squar with N d.o.f. May 2 '17 at 14:28
• @noob2 - I think it is N-1 degrees of freedom, but otherwise spot on because of the non-overlapping (independent) increments of equal time length. May 2 '17 at 20:05

## 1 Answer

I assume the OP means what is the variance, across N paths of M steps each, of the realised volatility of the GBM.

You would imagine that it is related to the dt-step size implied by M. i.e. for lower M, the variance of the pathwise-estimated volatility increases.

Feels like is related to strike adjustments for variance swaps with discrete observations, not sure if there is literature out for that but worth googling