Weak law of large numbers for reciprocal of normal












1














In two different journal articles:



The First Negative Moment of Skew-t and Generalized Student's t-Distributions in the Principal Value Sense



and



The first negative moment in the sense of the Cauchy principal value



the concept of the principal valued first moment is presented in the case where the first moment of a r.v. does not exist. The principal valued first moment (a.k.a. principal valued first negative moment FNM) for a continuous r.v. is defined by
begin{equation}
PV!E(Y^{-1}) = lim_{epsilonto0^+}left(int_{-infty}^{-epsilon}+int_{epsilon}^inftyright)frac{1}{y}f_Y(y),mathrm dy.
end{equation}



The author makes the following assertion in both articles:




Hence, through different viewpoints
of the integral of FNM, the concept of the (Cauchy) principal
value, widely used in the probability theory such as the
weak law of large numbers [11], can be used to avoid the
nonexistence of the FNM in the usual sense.




The same citation is used both times which is Feller's An Introduction to Probability Theory and its Applications vol. 2.



My question is simple: How is the FNM used in the weak law of large numbers? Is there a version of the WLLN for r.v's without moments that makes use of the FNM?



I found the following generalization of the WLLN in Feller's book (VII.7) for sequences of i.i.d. r.v's



begin{equation}
frac{S_n-nmathrm EXI{|X|leq n}}{n}overset{p}{to}0 text{as} ntoinftyiff x,mathsf P(|X|>x)to 0 text{as} xtoinfty.
end{equation}



I checked this condition for the reciprocal normal, i.e. $X=Y^{-1}$ for $Ysimmathcal N(mu,sigma^2)$ and found that
begin{equation}
lim_{xtoinfty}x,mathsf P(|X|>x)=2f_Y(0)neq 0.
end{equation}

So it would seem that Feller's WLLN does not apply. Can someone help me understand the claim made in the papers? Where is the FNM used in the WLLN?










share|cite|improve this question





























    1














    In two different journal articles:



    The First Negative Moment of Skew-t and Generalized Student's t-Distributions in the Principal Value Sense



    and



    The first negative moment in the sense of the Cauchy principal value



    the concept of the principal valued first moment is presented in the case where the first moment of a r.v. does not exist. The principal valued first moment (a.k.a. principal valued first negative moment FNM) for a continuous r.v. is defined by
    begin{equation}
    PV!E(Y^{-1}) = lim_{epsilonto0^+}left(int_{-infty}^{-epsilon}+int_{epsilon}^inftyright)frac{1}{y}f_Y(y),mathrm dy.
    end{equation}



    The author makes the following assertion in both articles:




    Hence, through different viewpoints
    of the integral of FNM, the concept of the (Cauchy) principal
    value, widely used in the probability theory such as the
    weak law of large numbers [11], can be used to avoid the
    nonexistence of the FNM in the usual sense.




    The same citation is used both times which is Feller's An Introduction to Probability Theory and its Applications vol. 2.



    My question is simple: How is the FNM used in the weak law of large numbers? Is there a version of the WLLN for r.v's without moments that makes use of the FNM?



    I found the following generalization of the WLLN in Feller's book (VII.7) for sequences of i.i.d. r.v's



    begin{equation}
    frac{S_n-nmathrm EXI{|X|leq n}}{n}overset{p}{to}0 text{as} ntoinftyiff x,mathsf P(|X|>x)to 0 text{as} xtoinfty.
    end{equation}



    I checked this condition for the reciprocal normal, i.e. $X=Y^{-1}$ for $Ysimmathcal N(mu,sigma^2)$ and found that
    begin{equation}
    lim_{xtoinfty}x,mathsf P(|X|>x)=2f_Y(0)neq 0.
    end{equation}

    So it would seem that Feller's WLLN does not apply. Can someone help me understand the claim made in the papers? Where is the FNM used in the WLLN?










    share|cite|improve this question



























      1












      1








      1







      In two different journal articles:



      The First Negative Moment of Skew-t and Generalized Student's t-Distributions in the Principal Value Sense



      and



      The first negative moment in the sense of the Cauchy principal value



      the concept of the principal valued first moment is presented in the case where the first moment of a r.v. does not exist. The principal valued first moment (a.k.a. principal valued first negative moment FNM) for a continuous r.v. is defined by
      begin{equation}
      PV!E(Y^{-1}) = lim_{epsilonto0^+}left(int_{-infty}^{-epsilon}+int_{epsilon}^inftyright)frac{1}{y}f_Y(y),mathrm dy.
      end{equation}



      The author makes the following assertion in both articles:




      Hence, through different viewpoints
      of the integral of FNM, the concept of the (Cauchy) principal
      value, widely used in the probability theory such as the
      weak law of large numbers [11], can be used to avoid the
      nonexistence of the FNM in the usual sense.




      The same citation is used both times which is Feller's An Introduction to Probability Theory and its Applications vol. 2.



      My question is simple: How is the FNM used in the weak law of large numbers? Is there a version of the WLLN for r.v's without moments that makes use of the FNM?



      I found the following generalization of the WLLN in Feller's book (VII.7) for sequences of i.i.d. r.v's



      begin{equation}
      frac{S_n-nmathrm EXI{|X|leq n}}{n}overset{p}{to}0 text{as} ntoinftyiff x,mathsf P(|X|>x)to 0 text{as} xtoinfty.
      end{equation}



      I checked this condition for the reciprocal normal, i.e. $X=Y^{-1}$ for $Ysimmathcal N(mu,sigma^2)$ and found that
      begin{equation}
      lim_{xtoinfty}x,mathsf P(|X|>x)=2f_Y(0)neq 0.
      end{equation}

      So it would seem that Feller's WLLN does not apply. Can someone help me understand the claim made in the papers? Where is the FNM used in the WLLN?










      share|cite|improve this question















      In two different journal articles:



      The First Negative Moment of Skew-t and Generalized Student's t-Distributions in the Principal Value Sense



      and



      The first negative moment in the sense of the Cauchy principal value



      the concept of the principal valued first moment is presented in the case where the first moment of a r.v. does not exist. The principal valued first moment (a.k.a. principal valued first negative moment FNM) for a continuous r.v. is defined by
      begin{equation}
      PV!E(Y^{-1}) = lim_{epsilonto0^+}left(int_{-infty}^{-epsilon}+int_{epsilon}^inftyright)frac{1}{y}f_Y(y),mathrm dy.
      end{equation}



      The author makes the following assertion in both articles:




      Hence, through different viewpoints
      of the integral of FNM, the concept of the (Cauchy) principal
      value, widely used in the probability theory such as the
      weak law of large numbers [11], can be used to avoid the
      nonexistence of the FNM in the usual sense.




      The same citation is used both times which is Feller's An Introduction to Probability Theory and its Applications vol. 2.



      My question is simple: How is the FNM used in the weak law of large numbers? Is there a version of the WLLN for r.v's without moments that makes use of the FNM?



      I found the following generalization of the WLLN in Feller's book (VII.7) for sequences of i.i.d. r.v's



      begin{equation}
      frac{S_n-nmathrm EXI{|X|leq n}}{n}overset{p}{to}0 text{as} ntoinftyiff x,mathsf P(|X|>x)to 0 text{as} xtoinfty.
      end{equation}



      I checked this condition for the reciprocal normal, i.e. $X=Y^{-1}$ for $Ysimmathcal N(mu,sigma^2)$ and found that
      begin{equation}
      lim_{xtoinfty}x,mathsf P(|X|>x)=2f_Y(0)neq 0.
      end{equation}

      So it would seem that Feller's WLLN does not apply. Can someone help me understand the claim made in the papers? Where is the FNM used in the WLLN?







      probability-theory law-of-large-numbers cauchy-principal-value






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      edited Nov 28 at 17:51

























      asked Nov 28 at 17:46









      Aaron Hendrickson

      563410




      563410



























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