Financial models with long-tailed distributions and volatility clustering have been introduced to overcome problems with the realism of classical financial models. These classical models of financial time series typically assume homoskedasticity and normality cannot explain stylized phenomena such as skewness, heavy tails, and volatility clustering of the empirical asset returns in finance. In 1963, Benoit Mandelbrot first used the stable (or
-stable) distribution to model the empirical distributions which have the skewness and heavy-tail property. Since
-stable distributions have infinite
-th moments for all
, the tempered stable processes have been proposed for overcoming this limitation of the stable distribution.
On the other hand, GARCH models have been developed to explain the volatility clustering. In the GARCH model, the innovation (or residual) distributions are assumed to be a standard normal distribution, despite the fact that this assumption is often rejected empirically. For this reason, GARCH models with non-normal innovation distribution have been developed.
Many financial models with stable and tempered stable distributions together with volatility clustering have been developed and applied to risk management, option pricing, and portfolio selection.
A random variable
is called infinitely divisible if,
for each
, there are independent and identically-distributed random variables
![{\displaystyle Y_{n,1},Y_{n,2},\dots ,Y_{n,n}\,}](//wikimedia.org/api/rest_v1/media/math/render/svg/778d6f1e55734826ffb59723f9dc8bde7b74f1f2)
such that
![{\displaystyle Y{\stackrel {\mathrm {d} }{=}}\sum _{k=1}^{n}Y_{n,k},\,}](//wikimedia.org/api/rest_v1/media/math/render/svg/0aa5878241112ba2feb9f1015ac4327bf16cdb09)
where
denotes equality in distribution.
A Borel measure
on
is called a Lévy measure if
and
![{\displaystyle \int _{\mathbb {R} }(1\wedge |x^{2}|)\,\nu (dx)<\infty .}](//wikimedia.org/api/rest_v1/media/math/render/svg/b4e41b1a67a330c0d0712a405f58eb2ceff9d511)
If
is infinitely divisible, then the characteristic function
is given by
![{\displaystyle \phi _{Y}(u)=\exp \left(i\gamma u-{\frac {1}{2}}\sigma ^{2}u^{2}+\int _{-\infty }^{\infty }(e^{iux}-1-iux1_{|x|\leq 1})\,\nu (dx)\right),\sigma \geq 0,~~\gamma \in \mathbb {R} }](//wikimedia.org/api/rest_v1/media/math/render/svg/8abf97ca800a393a12f41465557b080062c9fecc)
where
,
and
is a Lévy measure.
Here the triple
is called a Lévy triplet of
. This triplet is unique. Conversely, for any choice
satisfying the conditions above, there exists an infinitely divisible random variable
whose characteristic function is given as
.
A real-valued random variable
is said to have an
-stable distribution if for any
, there
are a positive number
and a real number
such that
![{\displaystyle X_{1}+\cdots +X_{n}{\stackrel {\mathrm {d} }{=}}C_{n}X+D_{n},\,}](//wikimedia.org/api/rest_v1/media/math/render/svg/e3fb0db40756506fc5ef3702c962abf71a3118f2)
where
are independent and have the same
distribution as that of
. All stable random variables are infinitely divisible. It is known that
for some
. A stable random
variable
with index
is called an
-stable random variable.
Let
be an
-stable random variable. Then the
characteristic function
of
is given by
![{\displaystyle \phi _{X}(u)={\begin{cases}\exp \left(i\mu u-\sigma ^{\alpha }|u|^{\alpha }\left(1-i\beta \operatorname {sgn} (u)\tan \left({\frac {\pi \alpha }{2}}\right)\right)\right)&{\text{if }}\alpha \in (0,1)\cup (1,2)\\\exp \left(i\mu u-\sigma |u|\left(1+i\beta \operatorname {sgn} (u)\left({\frac {2}{\pi }}\right)\ln(|u|)\right)\right)&{\text{if }}\alpha =1\\\exp \left(i\mu u-{\frac {1}{2}}\sigma ^{2}u^{2}\right)&{\text{if }}\alpha =2\end{cases}}}](//wikimedia.org/api/rest_v1/media/math/render/svg/447deb15488076d3930f06e9acf89a54ea422119)
for some
,
and
.
An infinitely divisible distribution is called a classical tempered stable (CTS) distribution with parameter
,
if its Lévy triplet
is given by
,
and
![{\displaystyle \nu (dx)=\left({\frac {C_{1}e^{-\lambda _{+}x}}{x^{1+\alpha }}}1_{x>0}+{\frac {C_{2}e^{-\lambda _{-}|x|}}{|x|^{1+\alpha }}}1_{x<0}\right)\,dx,}](//wikimedia.org/api/rest_v1/media/math/render/svg/ae47a6ac00b847c3611cfdfe9f4d7e84dd171147)
where
and
.
This distribution was first introduced by under
the name of Truncated Lévy Flights[1] and has been called the tempered stable or the KoBoL distribution.[2] In particular, if
, then this distribution is called the CGMY
distribution which has been used for
financial modeling.[3]
The characteristic function
for a tempered stable
distribution is given by
![{\displaystyle \phi _{CTS}(u)=\exp \left(iu\mu +C_{1}\Gamma (-\alpha )((\lambda _{+}-iu)^{\alpha }-\lambda _{+}^{\alpha })+C_{2}\Gamma (-\alpha )((\lambda _{-}+iu)^{\alpha }-\lambda _{-}^{\alpha })\right),}](//wikimedia.org/api/rest_v1/media/math/render/svg/c6ca3c0f13cbb014c99101f275daf46fc16f3e68)
for some
. Moreover,
can be extended to the
region :\operatorname {Im} (z)\in (-\lambda _{-},\lambda _{+})\}}
.
Rosiński generalized the CTS distribution under the name of the
tempered stable distribution. The KR distribution, which is a subclass of the Rosiński's generalized tempered stable distributions, is used in finance.[4]
An infinitely divisible distribution is called a modified tempered stable (MTS) distribution with parameter
,
if its Lévy triplet
is given by
,
and
![{\displaystyle \nu (dx)=C\left({\frac {q_{\alpha }(\lambda _{+}|x|)}{x^{\alpha +1}}}1_{x>0}+{\frac {q_{\alpha }(\lambda _{-}|x|)}{|x|^{\alpha +1}}}1_{x<0}\right)\,dx,}](//wikimedia.org/api/rest_v1/media/math/render/svg/c2db7d00162b3fd17b2198bc9148a4bb7e4cfc4c)
where
and
![{\displaystyle q_{\alpha }(x)=x^{\frac {\alpha +1}{2}}K_{\frac {\alpha +1}{2}}(x).}](//wikimedia.org/api/rest_v1/media/math/render/svg/ed86a50867ec5869f87e83e48c1c68a8c7080ea1)
Here
is the modified Bessel function of the second kind.
The MTS distribution is not included in the class of Rosiński's generalized tempered stable distributions.[5]
In order to describe the volatility clustering effect of the return process of an asset, the GARCH model can be used. In the GARCH model, innovation (
) is assumed that
, where
and where
the series
are modeled by
![{\displaystyle \sigma _{t}^{2}=\alpha _{0}+\alpha _{1}\epsilon _{t-1}^{2}+\cdots +\alpha _{q}\epsilon _{t-q}^{2}=\alpha _{0}+\sum _{i=1}^{q}\alpha _{i}\epsilon _{t-i}^{2}}](//wikimedia.org/api/rest_v1/media/math/render/svg/613b3ca3da387bdb47d7a6d3c0b7afbf493e8173)
and where
and
.
However, the assumption of
is often rejected empirically. For that reason, new GARCH models with stable or tempered stable distributed innovation have been developed. GARCH models with
-stable innovations have been introduced.[6][7][8] Subsequently, GARCH Models with tempered stable innovations have been developed.[5][9]
Objections against the use of stable distributions in Financial models are given in [10][11]
Koponen, I. (1995) "Analytic approach to the problem of convergence of truncated Lévy flights towards the Gaussian stochastic process", Physical Review E, 52, 1197–1199.
S. I. Boyarchenko, S. Z. Levendorskiǐ (2000) "Option pricing for truncated Lévy processes", International Journal of Theoretical and Applied Finance, 3 (3), 549–552
P. Carr, H. Geman, D. Madan, M. Yor (2002) "The Fine Structure of Asset Returns: An Empirical Investigation", Journal of Business, 75 (2), 305–332.
Kim, Y.S.; Rachev, Svetlozar T.;, Bianchi, M.L.; Fabozzi, F.J. (2007) "A New Tempered Stable Distribution and Its Application to Finance". In: Georg Bol, Svetlozar T. Rachev, and Reinold Wuerth (Eds.), Risk Assessment: Decisions in Banking and Finance, Physika Verlag, Springer Kim, Y.S., Chung, D. M., Rachev, Svetlozar T.; M. L. Bianchi, The modified tempered stable distribution, GARCH models and option pricing, Probability and Mathematical Statistics, to appear
C. Menn, Svetlozar T. Rachev (2005) "A GARCH Option Pricing Model with
-stable Innovations", European Journal of Operational Research, 163, 201–209 Svetlozar T. Rachev, C. Menn, Frank J. Fabozzi (2005) Fat-Tailed and Skewed Asset Return Distributions: Implications for Risk Management, Portfolio selection, and Option Pricing, Wiley Kim, Y.S.; Rachev, Svetlozar T.; Michele L. Bianchi, Fabozzi, F.J. (2008) "Financial market models with Lévy processes and time-varying volatility", Journal of Banking & Finance, 32 (7), 1363–1378 doi:10.1016/j.jbankfin.2007.11.004 Lev B. Klebanov, Irina Volchenkova (2015) "Heavy Tailed Distributions in Finance: Reality or Mith? Amateurs Viewpoint", arXiv:1507.07735v1, 1-17.
Lev B Klebanov (2016) "No Stable Distributions in Finance, please!", arXiv:1601.00566v2, 1-9.
- B. B. Mandelbrot (1963) "New Methods in Statistical Economics", Journal of Political Economy, 71, 421-440
- Svetlozar T. Rachev, Stefan Mittnik (2000) Stable Paretian Models in Finance, Wiley
- G. Samorodnitsky and M. S. Taqqu, Stable Non-Gaussian Random Processes, Chapman & Hall/CRC.
- S. I. Boyarchenko, S. Z. Levendorskiǐ (2000) "Option pricing for truncated Lévy processes", International Journal of Theoretical and Applied Finance, 3 (3), 549–552.
- J. Rosiński (2007) "Tempering Stable Processes", Stochastic Processes and their Applications, 117 (6), 677–707.