“重尾分布”的版本间的差异

来自集智百科 - 复杂系统|人工智能|复杂科学|复杂网络|自组织
跳到导航 跳到搜索
第165行: 第165行:
 
胖尾分布是这样的分布,对于较大的x,概率密度函数为<math>x^{-a}</math>趋于零。由于这样的幂总是受到指数分布概率密度函数的限制,因此,胖尾分布始终是重尾分布。但是,某些分布的尾部趋近于零的速率比指数函数慢(表示它们是重尾),而比幂快(表示它们不是胖尾)。例如对数正态分布<ref>{{Contradict-inline|article=fat-tailed distribution|reason=Fat-tailed page says log-normals are in fact fat-tailed.|date=June 2019}}</ref>。当然,许多其他的重尾分布,例如对数逻辑分布和帕累托分布也属于胖尾分布。
 
胖尾分布是这样的分布,对于较大的x,概率密度函数为<math>x^{-a}</math>趋于零。由于这样的幂总是受到指数分布概率密度函数的限制,因此,胖尾分布始终是重尾分布。但是,某些分布的尾部趋近于零的速率比指数函数慢(表示它们是重尾),而比幂快(表示它们不是胖尾)。例如对数正态分布<ref>{{Contradict-inline|article=fat-tailed distribution|reason=Fat-tailed page says log-normals are in fact fat-tailed.|date=June 2019}}</ref>。当然,许多其他的重尾分布,例如对数逻辑分布和帕累托分布也属于胖尾分布。
  
== Estimating the tail-index{{definition|date=January 2018}} 尾指数估计 ==
+
== 尾指数估计 ==
  
There are parametric (see Embrechts et al.<ref name="Embrechts"/>) and non-parametric (see, e.g., Novak<ref name="Novak2011">{{cite book
 
| author=Novak S.Y.
 
| title=Extreme value methods with applications to finance
 
| year=2011
 
| series=London: CRC
 
| isbn=978-1-43983-574-6
 
}}</ref>) approaches to the problem of the tail-index estimation.
 
  
 
对于尾指数估计的问题,有参数方法(参见Emprechts等人<ref name="Embrechts"/>)和非参数方法(例如,Novak<ref name="Novak2011">{{cite book
 
对于尾指数估计的问题,有参数方法(参见Emprechts等人<ref name="Embrechts"/>)和非参数方法(例如,Novak<ref name="Novak2011">{{cite book
第184行: 第177行:
  
  
 
To estimate the tail-index using the parametric approach, some authors employ  [[GEV distribution]] or [[Pareto distribution]]; they may apply the maximum-likelihood estimator (MLE).
 
  
 
为了使用参数化方法估计尾指数,有些作者采用了GEV分布或帕累托分布;他们可能会运用极大似然估计方法(MLE)。
 
为了使用参数化方法估计尾指数,有些作者采用了GEV分布或帕累托分布;他们可能会运用极大似然估计方法(MLE)。
第191行: 第182行:
  
  
=== Pickand's tail-index estimator  Pickand的尾指数估算器===
+
=== Pickand的尾指数估算器===
  
With <math>(X_n , n \geq 1)</math> a random sequence of independent and same  density function <math>F \in D(H(\xi))</math>, the Maximum Attraction Domain<ref name=Pickands>{{cite journal|last=Pickands III|first=James|title=Statistical Inference Using Extreme Order Statistics|journal=The Annals of Statistics|date=Jan 1975|volume=3|issue=1|pages=119–131|jstor=2958083|doi=10.1214/aos/1176343003|doi-access=free}}</ref>  of the generalized extreme value density <math> H </math>, where <math>\xi \in \mathbb{R}</math>. If <math>\lim_{n\to\infty} k(n) = \infty  </math> and  <math>\lim_{n\to\infty} \frac{k(n)}{n}= 0</math>, then the ''Pickands'' tail-index estimation is<ref name="Embrechts"/><ref name="Pickands"/>
 
  
 
对于<math>(X_n , n \geq 1)</math>的独立且相同的密度函数<math>F \in D(H(\xi))</math>的随机序列,是<font color="#ff8000">广义极值密度 the generalized extreme value density </font><math>H</math>的<font color="#ff8000">最大吸引域 the Maximum Attraction Domain </font><ref name=Pickands>{{cite journal|last=Pickands III|first=James|title=Statistical Inference Using Extreme Order Statistics|journal=The Annals of Statistics|date=Jan 1975|volume=3|issue=1|pages=119–131|jstor=2958083|doi=10.1214/aos/1176343003|doi-access=free}}</ref>,其中<math>\xi \in \mathbb{R}</math>。如果<math>\lim_{n\to\infty} k(n) = \infty  </math>和<math>\lim_{n\to\infty} \frac{k(n)}{n}= 0</math>,则Pickands尾部指数估计为<ref name="Embrechts"/><ref name="Pickands"/>
 
对于<math>(X_n , n \geq 1)</math>的独立且相同的密度函数<math>F \in D(H(\xi))</math>的随机序列,是<font color="#ff8000">广义极值密度 the generalized extreme value density </font><math>H</math>的<font color="#ff8000">最大吸引域 the Maximum Attraction Domain </font><ref name=Pickands>{{cite journal|last=Pickands III|first=James|title=Statistical Inference Using Extreme Order Statistics|journal=The Annals of Statistics|date=Jan 1975|volume=3|issue=1|pages=119–131|jstor=2958083|doi=10.1214/aos/1176343003|doi-access=free}}</ref>,其中<math>\xi \in \mathbb{R}</math>。如果<math>\lim_{n\to\infty} k(n) = \infty  </math>和<math>\lim_{n\to\infty} \frac{k(n)}{n}= 0</math>,则Pickands尾部指数估计为<ref name="Embrechts"/><ref name="Pickands"/>
第203行: 第193行:
  
  
where <math>X_{(n-k(n)+1,n)}=\max \left(X_{n-k(n)+1},\ldots  ,X_{n}\right)</math>. This estimator converges in probability to <math>\xi</math>.
 
  
 
其中<math>X_{(n-k(n)+1,n)}=\max \left(X_{n-k(n)+1},\ldots  ,X_{n}\right)</math>。 此估计量的概率收敛到<math>\xi</math>。
 
其中<math>X_{(n-k(n)+1,n)}=\max \left(X_{n-k(n)+1},\ldots  ,X_{n}\right)</math>。 此估计量的概率收敛到<math>\xi</math>。
第209行: 第198行:
  
  
=== Hill's tail-index estimator 希尔 Hill的尾指数估算器 ===
+
=== Hill的尾指数估算器 ===
  
Let <math>(X_t , t \geq 1)</math> be a sequence of independent and identically distributed random variables with distribution function <math>F \in D(H(\xi))</math>, the maximum domain of attraction of the [[generalized extreme value distribution]] <math> H </math>, where <math>\xi \in \mathbb{R}</math>. The sample path is <math>{X_t: 1 \leq t \leq n}</math> where <math>n</math> is the sample size. If
 
<math>\{k(n)\}</math> is an intermediate order sequence, i.e. <math>k(n) \in \{1,\ldots,n-1\}, </math>, <math>k(n) \to \infty</math> and  <math>k(n)/n \to 0</math>, then the Hill tail-index estimator is<ref>Hill B.M. (1975) A simple general approach to inference about  the tail of a distribution. Ann. Stat., v. 3, 1163–1174.</ref>
 
  
 
令<math>(X_t , t \geq 1)</math>为具有分布函数<math>F \in D(H(\xi))</math>独立且均匀分布的随机变量序列,其分布函数为广义极值分布<math> H </math>的最大吸引域,其中<math>\xi \in \mathbb{R}</math>。样本路径为<math>{X_t: 1 \leq t \leq n}</math>,其中<math>n</math>为样本大小。 如果<math>\{k(n)\}</math>是中间阶数序列,即<math>k(n) \in \{1,\ldots,n-1\}, </math>,<math>k(n) \to \infty</math>和<math>k(n)/n \to 0</math>,则Hill尾指数估计器为<ref>Hill B.M. (1975) A simple general approach to inference about  the tail of a distribution. Ann. Stat., v. 3, 1163–1174.</ref>:
 
令<math>(X_t , t \geq 1)</math>为具有分布函数<math>F \in D(H(\xi))</math>独立且均匀分布的随机变量序列,其分布函数为广义极值分布<math> H </math>的最大吸引域,其中<math>\xi \in \mathbb{R}</math>。样本路径为<math>{X_t: 1 \leq t \leq n}</math>,其中<math>n</math>为样本大小。 如果<math>\{k(n)\}</math>是中间阶数序列,即<math>k(n) \in \{1,\ldots,n-1\}, </math>,<math>k(n) \to \infty</math>和<math>k(n)/n \to 0</math>,则Hill尾指数估计器为<ref>Hill B.M. (1975) A simple general approach to inference about  the tail of a distribution. Ann. Stat., v. 3, 1163–1174.</ref>:
第222行: 第209行:
  
  
where <math>X_{(i,n)}</math> is the <math>i</math>-th [[order statistic]] of <math>X_1, \dots, X_n</math>.
 
This estimator converges in probability to <math>\xi</math>, and is asymptotically normal provided <math>k(n) \to \infty  </math> is restricted based on a higher order regular variation property<ref>Hall, P.(1982) On some estimates of an exponent of regular variation. J. R. Stat. Soc. Ser. B., v. 44, 37–42.</ref>
 
.<ref>Haeusler, E. and J. L. Teugels (1985) On asymptotic normality of Hill's estimator for the exponent of regular variation. Ann. Stat., v. 13, 743–756.</ref> Consistency and asymptotic normality extend to a large class of dependent and heterogeneous sequences,<ref>Hsing, T. (1991) On tail index estimation using dependent data. Ann. Stat., v. 19, 1547–1569.</ref><ref>Hill, J. (2010) On tail index estimation for dependent, heterogeneous data. Econometric Th., v. 26, 1398–1436.</ref> irrespective of whether <math>X_t</math> is observed, or a computed residual or filtered data from a large class of models and estimators, including mis-specified models and models with errors that are dependent.<ref>Resnick, S. and Starica, C. (1997). Asymptotic behavior of Hill’s estimator for autoregressive data. Comm. Statist. Stochastic Models 13, 703–721.</ref><ref>Ling, S. and Peng, L. (2004). Hill’s estimator for the tail index of an ARMA model. J. Statist. Plann. Inference 123, 279–293.</ref><ref>Hill, J. B. (2015). Tail index estimation for a filtered dependent time series. Stat. Sin. 25, 609–630.</ref>
 
  
 
其中<math>X_{(i,n)}</math>是<math>X_1, \dots, X_n</math>的第<math>i</math>次序统计量。该估计量依概率收敛于<math>\xi</math>,并且在基于高阶的正则变化性质的情况下,是限制<math>k(n) \to \infty  </math>的渐近正态<ref>Hall, P.(1982) On some estimates of an exponent of regular variation. J. R. Stat. Soc. Ser. B., v. 44, 37–42.</ref>.<ref>Haeusler, E. and J. L. Teugels (1985) On asymptotic normality of Hill's estimator for the exponent of regular variation. Ann. Stat., v. 13, 743–756.</ref>。一致性和渐近正态性适用于一大类相关序列和异类序列<ref>Hsing, T. (1991) On tail index estimation using dependent data. Ann. Stat., v. 19, 1547–1569.</ref><ref>Hill, J. (2010) On tail index estimation for dependent, heterogeneous data. Econometric Th., v. 26, 1398–1436.</ref>,而不管是否观测到<math>X_t</math>,或者来自大量模型和估计量(包括错误指定的模型和具有相关误差的模型)计算出的残差或筛选数据。<ref>Resnick, S. and Starica, C. (1997). Asymptotic behavior of Hill’s estimator for autoregressive data. Comm. Statist. Stochastic Models 13, 703–721.</ref><ref>Ling, S. and Peng, L. (2004). Hill’s estimator for the tail index of an ARMA model. J. Statist. Plann. Inference 123, 279–293.</ref><ref>Hill, J. B. (2015). Tail index estimation for a filtered dependent time series. Stat. Sin. 25, 609–630.</ref>
 
其中<math>X_{(i,n)}</math>是<math>X_1, \dots, X_n</math>的第<math>i</math>次序统计量。该估计量依概率收敛于<math>\xi</math>,并且在基于高阶的正则变化性质的情况下,是限制<math>k(n) \to \infty  </math>的渐近正态<ref>Hall, P.(1982) On some estimates of an exponent of regular variation. J. R. Stat. Soc. Ser. B., v. 44, 37–42.</ref>.<ref>Haeusler, E. and J. L. Teugels (1985) On asymptotic normality of Hill's estimator for the exponent of regular variation. Ann. Stat., v. 13, 743–756.</ref>。一致性和渐近正态性适用于一大类相关序列和异类序列<ref>Hsing, T. (1991) On tail index estimation using dependent data. Ann. Stat., v. 19, 1547–1569.</ref><ref>Hill, J. (2010) On tail index estimation for dependent, heterogeneous data. Econometric Th., v. 26, 1398–1436.</ref>,而不管是否观测到<math>X_t</math>,或者来自大量模型和估计量(包括错误指定的模型和具有相关误差的模型)计算出的残差或筛选数据。<ref>Resnick, S. and Starica, C. (1997). Asymptotic behavior of Hill’s estimator for autoregressive data. Comm. Statist. Stochastic Models 13, 703–721.</ref><ref>Ling, S. and Peng, L. (2004). Hill’s estimator for the tail index of an ARMA model. J. Statist. Plann. Inference 123, 279–293.</ref><ref>Hill, J. B. (2015). Tail index estimation for a filtered dependent time series. Stat. Sin. 25, 609–630.</ref>
第230行: 第214行:
  
  
=== Ratio estimator of the tail-index 尾部指数的比率估计器 ===
+
===尾部指数的比率估计器 ===
  
The ratio estimator (RE-estimator) of the tail-index was introduced by Goldie 
 
and Smith.<ref>Goldie C.M., Smith R.L. (1987) Slow variation with remainder:
 
theory and applications. Quart. J. Math. Oxford, v. 38, 45–71.</ref>
 
It is constructed similarly to Hill's estimator but uses a non-random "tuning parameter".
 
  
 
尾指数的比率估计器(RE估计器)由Goldie和Smith提出<ref>Goldie C.M., Smith R.L. (1987) Slow variation with remainder:
 
尾指数的比率估计器(RE估计器)由Goldie和Smith提出<ref>Goldie C.M., Smith R.L. (1987) Slow variation with remainder:
第242行: 第222行:
  
  
A comparison of Hill-type and RE-type estimators can be found in Novak.<ref name="Novak2011"/>
 
  
 
在Novak中可以找到Hill型和RE型估计量的比较。<ref name="Novak2011"/>
 
在Novak中可以找到Hill型和RE型估计量的比较。<ref name="Novak2011"/>
  
=== Software 应用软件===
+
===应用软件===
* [http://www.cs.bu.edu/~crovella/aest.html aest], [[C (programming language)|C]] tool for estimating the heavy-tail index.<ref>{{Cite journal | last1 = Crovella | first1 = M. E. | last2 = Taqqu | first2 = M. S. | title = Estimating the Heavy Tail Index from Scaling Properties| journal = Methodology and Computing in Applied Probability | volume = 1 | pages = 55–79 | year = 1999 | doi = 10.1023/A:1010012224103 | url = http://www.cs.bu.edu/~crovella/paper-archive/aest.ps| pmid =  | pmc = }}</ref>
 
  
 
* 用于估计重尾指数的软件[http://www.cs.bu.edu/~crovella/aest.html aest]和C。<ref>{{Cite journal | last1 = Crovella | first1 = M. E. | last2 = Taqqu | first2 = M. S. | title = Estimating the Heavy Tail Index from Scaling Properties| journal = Methodology and Computing in Applied Probability | volume = 1 | pages = 55–79 | year = 1999 | doi = 10.1023/A:1010012224103 | url = http://www.cs.bu.edu/~crovella/paper-archive/aest.ps| pmid =  | pmc = }}</ref>
 
* 用于估计重尾指数的软件[http://www.cs.bu.edu/~crovella/aest.html aest]和C。<ref>{{Cite journal | last1 = Crovella | first1 = M. E. | last2 = Taqqu | first2 = M. S. | title = Estimating the Heavy Tail Index from Scaling Properties| journal = Methodology and Computing in Applied Probability | volume = 1 | pages = 55–79 | year = 1999 | doi = 10.1023/A:1010012224103 | url = http://www.cs.bu.edu/~crovella/paper-archive/aest.ps| pmid =  | pmc = }}</ref>

2021年2月26日 (五) 15:58的版本

此词条Jie翻译。已由Smile审校。


在概率论中,重尾分布 Heavy-tailed distributions是指其尾部呈现出不受指数限制的概率分布[1]:也就是说,它们的尾部比指数分布 exponential distribution “重”。在许多应用中,关注的是分布的右尾,但是分布的左尾可能也很重,或者两个尾都很重。


重尾分布有三个重要的子类:胖尾分布 Fat-tailed distribution长尾分布 Long-tailed distribution次指数分布 Subexponential distributions。实际上,所有常用的重尾分布都属于次指数分布类 subexponential class



在使用“重尾” Heavy-tailed一词时仍存在一些歧义。于是就出现了另外两种定义。一些作者使用该术语来指代并非所有幂矩都是有限的那些分布,以及其它一些没有有限方差的分布。本文中给出的是最常用的定义,包括替代定义所涵盖的所有分布,以及具有所有幂矩的对数正态分布 long-normal distributions ,但通常被认为是重尾的。(有时“重尾”用于任何具有比正态分布更重的尾巴的分布。)


定义

重尾分布的定义

如果[math]\displaystyle{ X }[/math]的矩生成函数, [math]\displaystyle{ M\lt sub\gt X\lt /sub\gt }[/math]([math]\displaystyle{ t }[/math])对于所有[math]\displaystyle{ t }[/math] > 0都是无限的,则具有分布函数[math]\displaystyle{ F }[/math]的随机变量[math]\displaystyle{ X }[/math]的分布被称为重尾(右)。[2]


也就是说:[math]\displaystyle{ \int_{-\infty}^\infty e^{t x} \,dF(x) = \infty \quad \mbox{for all } t\gt 0. }[/math]


这意味着:[math]\displaystyle{ \lim_{x \to \infty} e^{t x}\Pr[X\gt x] = \infty \quad \mbox{for all } t\gt 0.\, }[/math]


也可以写成尾分布函数 the tail distribution function

[math]\displaystyle{ \overline{F}(x) ≡ \Pr[X\gt x] }[/math]


as

[math]\displaystyle{ \lim_{x \to \infty} e^{t x}\overline{F}(x) = \infty \quad \mbox{for all } t \gt 0.\, }[/math]

长尾分布的定义

如果对于所有t>0,则称具有分布函数F的随机变量X的分布为有较长的右尾,

[math]\displaystyle{ \lim_{x \to \infty} \Pr[X\gt x+t\mid X\gt x] =1, \, }[/math]


或等同于

[math]\displaystyle{ \overline{F}(x+t) \sim \overline{F}(x) \quad \mbox{as } x \to \infty. \, }[/math]


对于右尾长尾分布量具有直观的解释,即如果长尾量超过某个高水平,则概率将接近1,它将超过其他更高的水平。


所有长尾分布都是重尾分布,但反过来不一定成立,且可以构造出非长尾分布的重尾分布。


次指数分布

次指数性是根据概率分布的卷积 Convolution 定义的。对于具有共同分布函数[math]\displaystyle{ F }[/math]的两个独立且分布均匀的随机变量[math]\displaystyle{ X_1,X_2 }[/math][math]\displaystyle{ F }[/math]与自身的卷积,[math]\displaystyle{ F^{*2} }[/math]是卷积的平方,使用Lebesgue–Stieltjes积分,方法如下:


[math]\displaystyle{ \Pr[X_1+X_2 \leq x] = F^{*2}(x) = \int_{0}^x F(x-y)\,dF(y), }[/math]


n倍卷积[math]\displaystyle{ F^{*n} }[/math]定义如下:


[math]\displaystyle{ F^{*n}(x) = \int_{0}^x F(x-y)\,dF^{*n-1}(y). }[/math]

尾分布函数[math]\displaystyle{ \overline{F} }[/math]定义为[math]\displaystyle{ \overline{F}(x) = 1-F(x) }[/math]



如果满足以下条件,则正半线上的分布[math]\displaystyle{ F }[/math]为次指数[1][3][4]


[math]\displaystyle{ \overline{F^{*2}}(x) \sim 2\overline{F}(x) \quad \mbox{as } x \to \infty. }[/math]


这意味着[5],对于任何[math]\displaystyle{ n \geq 1 }[/math]


[math]\displaystyle{ \overline{F^{*n}}(x) \sim n\overline{F}(x) \quad \mbox{as } x \to \infty. }[/math]


对此的概率解释[5]是,对于具有共同分布[math]\displaystyle{ F }[/math][math]\displaystyle{ n }[/math]个独立随机变量[math]\displaystyle{ X_1,\ldots,X_n }[/math]的总和


[math]\displaystyle{ \Pr[X_1+ \cdots +X_n\gt x] \sim \Pr[\max(X_1, \ldots,X_n)\gt x] \quad \text{as } x \to \infty. }[/math]


这通常被称为单跳 single big jump[6]突变理论 catastrophe principle [7]


如果分布[math]\displaystyle{ F I([0,\infty))\lt /m4ath\gt 为实数,则\lt math\gt F }[/math]为整个实数上的次指数分布。[8]此时[math]\displaystyle{ I([0,\infty)) }[/math]是正半轴的指标函数。或者,当且仅当[math]\displaystyle{ X^+ = \max(0,X) }[/math]是次指数时,实数上支持的随机变量[math]\displaystyle{ X }[/math]才是次指数。


所有次指数分布都是长尾分布,但可以构造出非次指数分布的长尾分布的示例。

常见的重尾分布

所有常用的重尾分布都是次指数的。[5]

Those that are one-tailed include: 单尾的包括:

  • 帕累托分布 Pareto distribution;
  • 对数正态分布 Log-normal distribution;
  • 莱维分布 Lévy distribution;
  • 形状参数大于0但小于1的韦布尔分布 Weibull distribution;
  • 伯尔分布 Burr distribution;
  • 对数逻辑分布 log-logistic distribution;
  • 对数伽玛分布 log-gamma distribution;
  • 弗雷歇分布 Fréchet distribution;
  • 对数柯西分布 log-Cauchy distribution,有时被描述为“超重尾”分布,因为它表现出对数衰减,从而产生比帕累托分布更重的尾。[9][10]

Those that are two-tailed include: 双尾的包括:

  • 柯西分布 Cauchy distribution本身就是稳定分布和t分布的特例;
  • 稳定分布族 The family of stable distributions[11],但该族中正态分布的特殊情况除外。一些稳定的分布是单面的(或有半线的支持),例如莱维分布。另请参见具有长尾分布和波动性聚类的财务模型。
  • t分布
  • 偏对数正态级联分布 The skew lognormal cascade distribution[12]

与胖尾分布的关系

胖尾分布是这样的分布,对于较大的x,概率密度函数为[math]\displaystyle{ x^{-a} }[/math]趋于零。由于这样的幂总是受到指数分布概率密度函数的限制,因此,胖尾分布始终是重尾分布。但是,某些分布的尾部趋近于零的速率比指数函数慢(表示它们是重尾),而比幂快(表示它们不是胖尾)。例如对数正态分布[13]。当然,许多其他的重尾分布,例如对数逻辑分布和帕累托分布也属于胖尾分布。

尾指数估计

对于尾指数估计的问题,有参数方法(参见Emprechts等人[5])和非参数方法(例如,Novak[14])两种。


为了使用参数化方法估计尾指数,有些作者采用了GEV分布或帕累托分布;他们可能会运用极大似然估计方法(MLE)。


Pickand的尾指数估算器

对于[math]\displaystyle{ (X_n , n \geq 1) }[/math]的独立且相同的密度函数[math]\displaystyle{ F \in D(H(\xi)) }[/math]的随机序列,是广义极值密度 the generalized extreme value density [math]\displaystyle{ H }[/math]最大吸引域 the Maximum Attraction Domain [15],其中[math]\displaystyle{ \xi \in \mathbb{R} }[/math]。如果[math]\displaystyle{ \lim_{n\to\infty} k(n) = \infty }[/math][math]\displaystyle{ \lim_{n\to\infty} \frac{k(n)}{n}= 0 }[/math],则Pickands尾部指数估计为[5][15]


[math]\displaystyle{ \xi^\text{Pickands}_{(k(n),n)} =\frac{1}{\ln 2} \ln \left( \frac{X_{(n-k(n)+1,n)} - X_{(n-2k(n)+1,n)}}{X_{(n-2k(n)+1,n)} - X_{(n-4k(n)+1,n)}}\right) }[/math]


其中[math]\displaystyle{ X_{(n-k(n)+1,n)}=\max \left(X_{n-k(n)+1},\ldots ,X_{n}\right) }[/math]。 此估计量的概率收敛到[math]\displaystyle{ \xi }[/math]


Hill的尾指数估算器

[math]\displaystyle{ (X_t , t \geq 1) }[/math]为具有分布函数[math]\displaystyle{ F \in D(H(\xi)) }[/math]独立且均匀分布的随机变量序列,其分布函数为广义极值分布[math]\displaystyle{ H }[/math]的最大吸引域,其中[math]\displaystyle{ \xi \in \mathbb{R} }[/math]。样本路径为[math]\displaystyle{ {X_t: 1 \leq t \leq n} }[/math],其中[math]\displaystyle{ n }[/math]为样本大小。 如果[math]\displaystyle{ \{k(n)\} }[/math]是中间阶数序列,即[math]\displaystyle{ k(n) \in \{1,\ldots,n-1\}, }[/math][math]\displaystyle{ k(n) \to \infty }[/math][math]\displaystyle{ k(n)/n \to 0 }[/math],则Hill尾指数估计器为[16]


[math]\displaystyle{ \xi^\text{Hill}_{(k(n),n)} = \left(\frac 1 {k(n)} \sum_{i=n-k(n)+1}^n \ln(X_{(i,n)}) - \ln (X_{(n-k(n)+1,n)})\right)^{-1}, }[/math]


其中[math]\displaystyle{ X_{(i,n)} }[/math][math]\displaystyle{ X_1, \dots, X_n }[/math]的第[math]\displaystyle{ i }[/math]次序统计量。该估计量依概率收敛于[math]\displaystyle{ \xi }[/math],并且在基于高阶的正则变化性质的情况下,是限制[math]\displaystyle{ k(n) \to \infty }[/math]的渐近正态[17].[18]。一致性和渐近正态性适用于一大类相关序列和异类序列[19][20],而不管是否观测到[math]\displaystyle{ X_t }[/math],或者来自大量模型和估计量(包括错误指定的模型和具有相关误差的模型)计算出的残差或筛选数据。[21][22][23]


尾部指数的比率估计器

尾指数的比率估计器(RE估计器)由Goldie和Smith提出[24]。它的构造类似于Hill估计器,但使用了非随机的“调整参数”



在Novak中可以找到Hill型和RE型估计量的比较。[14]

应用软件

  • 用于估计重尾指数的软件aest和C。[25]

Estimation of heavy-tailed density 重尾密度的估计

Nonparametric approaches to estimate heavy- and superheavy-tailed probability density functions were given in Markovich.[26] These are approaches based on variable bandwidth and long-tailed kernel estimators; on the preliminary data transform to a new random variable at finite or infinite intervals which is more convenient for the estimation and then inverse transform of the obtained density estimate; and "piecing-together approach" which provides a certain parametric model for the tail of the density and a non-parametric model to approximate the mode of the density. Nonparametric estimators require an appropriate selection of tuning (smoothing) parameters like a bandwidth of kernel estimators and the bin width of the histogram. The well known data-driven methods of such selection are a cross-validation and its modifications, methods based on the minimization of the mean squared error (MSE) and its asymptotic and their upper bounds.[27] A discrepancy method which uses well-known nonparametric statistics like Kolmogorov-Smirnov's, von Mises and Anderson-Darling's ones as a metric in the space of distribution functions (dfs) and quantiles of the later statistics as a known uncertainty or a discrepancy value can be found in.[26] Bootstrap is another tool to find smoothing parameters using approximations of unknown MSE by different schemes of re-samples selection, see e.g.[28]

Markovich中给出了估计重尾和超重尾概率密度函数的非参数方法。[26]这些是基于可变带宽 variable bandwidth长尾核估计器 long-tailed kernel estimators的方法。将初步数据以有限或无限间隔变换为新的随机变量,这样更便于估计,然后对获得的密度估计进行逆变换;以及“拼合方法”,它为密度的尾部提供了确定的参数模型,并为近似密度模型提供了非参数模型。非参数估计器需要适当选择调整(平滑)参数,例如内核估计器的带宽和直方图的组距。这种选择大众化数据驱动方法是基于均方误差(MSE)及其渐近或上限的最小化的交叉验证及修改方法。[27]可以找到一种差异方法,通过使用著名的非参数统计数据(例如Kolmogorov-Smirnov's,von Mises和Anderson-Darling的统计量)作为分布函数(dfs)空间中的度量,并将后来的统计量的分位数作为已知的不确定性或差异值。[26]自助法 Bootstrap是另一种工具,可以通过不同的重抽样方案使用未知MSE的近似值来查找平滑参数。[28]


See also 其他参考资料


  • 尖峭态分布 Leptokurtic distribution
  • 广义极值分布 Generalized extreme value distribution
  • 离群值 Outlier
  • 长尾 Long tail
  • 幂律 Power law
  • 随机的七个状态 Seven states of randomness
  • 胖尾分布 Fat-tailed distribution
    • 塔勒布分布 Taleb distribution圣杯分布 Holy grail distribution


References 参考文献

  1. 1.0 1.1 Asmussen, S. R. (2003). "Steady-State Properties of GI/G/1". Applied Probability and Queues. Stochastic Modelling and Applied Probability. 51. pp. 266–301. doi:10.1007/0-387-21525-5_10. ISBN 978-0-387-00211-8. 
  2. Rolski, Schmidli, Scmidt, Teugels, Stochastic Processes for Insurance and Finance, 1999
  3. Chistyakov, V. P. (1964). "A Theorem on Sums of Independent Positive Random Variables and Its Applications to Branching Random Processes". ResearchGate (in English). Retrieved April 7, 2019.
  4. Teugels, Jozef L. (1975). "The Class of Subexponential Distributions". University of Louvain: Annals of Probability. Retrieved April 7, 2019.
  5. 5.0 5.1 5.2 5.3 5.4 Embrechts P.; Klueppelberg C.; Mikosch T. (1997). Modelling extremal events for insurance and finance. Stochastic Modelling and Applied Probability. 33. Berlin: Springer. doi:10.1007/978-3-642-33483-2. ISBN 978-3-642-08242-9. 
  6. Foss, S.; Konstantopoulos, T.; Zachary, S. (2007). "Discrete and Continuous Time Modulated Random Walks with Heavy-Tailed Increments" (PDF). Journal of Theoretical Probability. 20 (3): 581. arXiv:math/0509605. CiteSeerX 10.1.1.210.1699. doi:10.1007/s10959-007-0081-2.
  7. Wierman, Adam (January 9, 2014). "Catastrophes, Conspiracies, and Subexponential Distributions (Part III)". Rigor + Relevance blog. RSRG, Caltech. Retrieved January 9, 2014.
  8. Willekens, E. (1986). "Subexponentiality on the real line". Technical Report. K.U. Leuven.
  9. Falk, M., Hüsler, J. & Reiss, R. (2010). Laws of Small Numbers: Extremes and Rare Events. Springer. p. 80. ISBN 978-3-0348-0008-2. 
  10. Alves, M.I.F., de Haan, L. & Neves, C. (March 10, 2006). "Statistical inference for heavy and super-heavy tailed distributions" (PDF). Archived from the original (PDF) on June 23, 2007. Retrieved November 1, 2011.{{cite web}}: CS1 maint: multiple names: authors list (link)
  11. John P. Nolan (2009). "Stable Distributions: Models for Heavy Tailed Data" (PDF). Retrieved 2009-02-21.
  12. Stephen Lihn (2009). "Skew Lognormal Cascade Distribution". Archived from the original on 2014-04-07. Retrieved 2009-06-12.
  13. 模板:Contradict-inline
  14. 14.0 14.1 Novak S.Y. (2011). Extreme value methods with applications to finance. London: CRC. ISBN 978-1-43983-574-6. 
  15. 15.0 15.1 Pickands III, James (Jan 1975). "Statistical Inference Using Extreme Order Statistics". The Annals of Statistics. 3 (1): 119–131. doi:10.1214/aos/1176343003. JSTOR 2958083.
  16. Hill B.M. (1975) A simple general approach to inference about the tail of a distribution. Ann. Stat., v. 3, 1163–1174.
  17. Hall, P.(1982) On some estimates of an exponent of regular variation. J. R. Stat. Soc. Ser. B., v. 44, 37–42.
  18. Haeusler, E. and J. L. Teugels (1985) On asymptotic normality of Hill's estimator for the exponent of regular variation. Ann. Stat., v. 13, 743–756.
  19. Hsing, T. (1991) On tail index estimation using dependent data. Ann. Stat., v. 19, 1547–1569.
  20. Hill, J. (2010) On tail index estimation for dependent, heterogeneous data. Econometric Th., v. 26, 1398–1436.
  21. Resnick, S. and Starica, C. (1997). Asymptotic behavior of Hill’s estimator for autoregressive data. Comm. Statist. Stochastic Models 13, 703–721.
  22. Ling, S. and Peng, L. (2004). Hill’s estimator for the tail index of an ARMA model. J. Statist. Plann. Inference 123, 279–293.
  23. Hill, J. B. (2015). Tail index estimation for a filtered dependent time series. Stat. Sin. 25, 609–630.
  24. Goldie C.M., Smith R.L. (1987) Slow variation with remainder: theory and applications. Quart. J. Math. Oxford, v. 38, 45–71.
  25. Crovella, M. E.; Taqqu, M. S. (1999). "Estimating the Heavy Tail Index from Scaling Properties". Methodology and Computing in Applied Probability. 1: 55–79. doi:10.1023/A:1010012224103.
  26. 26.0 26.1 26.2 26.3 Markovich N.M. (2007). Nonparametric Analysis of Univariate Heavy-Tailed data: Research and Practice. Chitester: Wiley. ISBN 978-0-470-72359-3. 
  27. 27.0 27.1 Wand M.P., Jones M.C. (1995). Kernel smoothing. New York: Chapman and Hall. ISBN 978-0412552700. 
  28. 28.0 28.1 Hall P. (1992). The Bootstrap and Edgeworth Expansion. Springer. ISBN 9780387945088. 


Category:Tails of probability distributions

类别: 概率分布的尾部

Category:Types of probability distributions

类别: 概率分布的类型

Category:Actuarial science

类别: 精算

Category:Risk

类别: 风险


This page was moved from wikipedia:en:Heavy-tailed distribution. Its edit history can be viewed at 重尾分布/edithistory