Saturday, October 14, 2017

fx - Why do we usually use normal distribution and not Laplace distribution to generate stochastic process?


When working with a stochastic process based on brownian motion, the increments have normal (gaussian) distribution.



However, it seems that a Laplace distribution, with density:


$$f(t) = \frac{\lambda}{2} e^{-\lambda |t|} \qquad (t \in \mathbb R)$$


would fit much more returns of EUR/USD for example than a normal distribution. (Especially, it has fatter tails than normal distribution, as required).


Here in blue is the density of returns, based on 10 years of historical data of 5-minutes chart of EUR/USD. In green, the density of a Laplace distribution.


enter image description here



Are there some financial models, in which the stochastic process used is:


$$d \, X_t = ... + c \, d \, W_t$$


where $d\, W_t$ has a Laplace distribution instead of a normal distribution?




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