If $F_X(x), F_Y(y)$ are two CDF's for r.v.'s $X$ and $Y$, will $F_{X,Y}(x,y) < F_X(x) cdot F_Y(y)$ if $X$...

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If $F_X(x), F_Y(y)$ are two CDF's for r.v.'s $X$ and $Y$, will $F_{X,Y}(x,y)



Announcing the arrival of Valued Associate #679: Cesar Manara
Planned maintenance scheduled April 17/18, 2019 at 00:00UTC (8:00pm US/Eastern)For random variables $X$ and $Y$, $F_{X,Y}(x,y)=F_X(x)F_Y(y)$ if and only if $f_{X,Y}(x,y)=f_X(x)f_Y(y)$If the PDF satisfies $f(x_1,y_1)f(x_2,y_2)leq f(x_1,y_2)f(x_2,y_1)$ then the CDF's satisfy $F(a,b)leq F_X(a)F_Y(b)$.What is CDF $F_X(x) $ and $F_Y(y)$?Prove $X$ and $Y$ are not independentHow to interpret the the fact that sum of two independent uniform r.v. forms a triangular distribution?Is $int_{-infty}^{infty}f_X(z-y)f_Y(y)dy$ a PDF where $f_x,f_Y$ are both PDFSProve that if $X,Y$ are independent random variables with densities $f_X, f_Y$ then,Showing that two random variables are independentHow to check if two random variables are independent without calculating their density functions?Clarifying the statement $f(x,y) = f_X(x) f_Y(y)$ for all $x, y$ (when $X$ and $Y$ are independent)












0












$begingroup$


If $F_X(x), F_Y(y)$ are two CDF's for r.v.'s $X$ and $Y$, if $X$ and $Y$ are independent, then:



$$
F_{X,Y}(x,y) = F_X(x) cdot F_Y(y)
$$



However, I am wondering more generally if



$$
F_{X,Y}(x,y) < F_X(x) cdot F_Y(y)
$$



if $X$ and $Y$ are not independent or if it depends how the joint distribution is constructed?










share|cite|improve this question









$endgroup$

















    0












    $begingroup$


    If $F_X(x), F_Y(y)$ are two CDF's for r.v.'s $X$ and $Y$, if $X$ and $Y$ are independent, then:



    $$
    F_{X,Y}(x,y) = F_X(x) cdot F_Y(y)
    $$



    However, I am wondering more generally if



    $$
    F_{X,Y}(x,y) < F_X(x) cdot F_Y(y)
    $$



    if $X$ and $Y$ are not independent or if it depends how the joint distribution is constructed?










    share|cite|improve this question









    $endgroup$















      0












      0








      0





      $begingroup$


      If $F_X(x), F_Y(y)$ are two CDF's for r.v.'s $X$ and $Y$, if $X$ and $Y$ are independent, then:



      $$
      F_{X,Y}(x,y) = F_X(x) cdot F_Y(y)
      $$



      However, I am wondering more generally if



      $$
      F_{X,Y}(x,y) < F_X(x) cdot F_Y(y)
      $$



      if $X$ and $Y$ are not independent or if it depends how the joint distribution is constructed?










      share|cite|improve this question









      $endgroup$




      If $F_X(x), F_Y(y)$ are two CDF's for r.v.'s $X$ and $Y$, if $X$ and $Y$ are independent, then:



      $$
      F_{X,Y}(x,y) = F_X(x) cdot F_Y(y)
      $$



      However, I am wondering more generally if



      $$
      F_{X,Y}(x,y) < F_X(x) cdot F_Y(y)
      $$



      if $X$ and $Y$ are not independent or if it depends how the joint distribution is constructed?







      probability






      share|cite|improve this question













      share|cite|improve this question











      share|cite|improve this question




      share|cite|improve this question










      asked Mar 23 at 23:33









      user321627user321627

      1,000515




      1,000515






















          1 Answer
          1






          active

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          4












          $begingroup$

          If $X=Y$ then $F_X(x)F_Y(x)=(F_X(x))^{2} <F_X(x)=F_{X,Y}(x,x)$ provided $F_X(x)<1$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            For cases not perfectly dependent, is there a general rule of thumb?
            $endgroup$
            – user321627
            Mar 24 at 2:42










          • $begingroup$
            No. there is no reason to expect an inequalilty of the type you have come up with.
            $endgroup$
            – Kavi Rama Murthy
            Mar 24 at 4:55












          Your Answer








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          1 Answer
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          1 Answer
          1






          active

          oldest

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          active

          oldest

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          active

          oldest

          votes









          4












          $begingroup$

          If $X=Y$ then $F_X(x)F_Y(x)=(F_X(x))^{2} <F_X(x)=F_{X,Y}(x,x)$ provided $F_X(x)<1$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            For cases not perfectly dependent, is there a general rule of thumb?
            $endgroup$
            – user321627
            Mar 24 at 2:42










          • $begingroup$
            No. there is no reason to expect an inequalilty of the type you have come up with.
            $endgroup$
            – Kavi Rama Murthy
            Mar 24 at 4:55
















          4












          $begingroup$

          If $X=Y$ then $F_X(x)F_Y(x)=(F_X(x))^{2} <F_X(x)=F_{X,Y}(x,x)$ provided $F_X(x)<1$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            For cases not perfectly dependent, is there a general rule of thumb?
            $endgroup$
            – user321627
            Mar 24 at 2:42










          • $begingroup$
            No. there is no reason to expect an inequalilty of the type you have come up with.
            $endgroup$
            – Kavi Rama Murthy
            Mar 24 at 4:55














          4












          4








          4





          $begingroup$

          If $X=Y$ then $F_X(x)F_Y(x)=(F_X(x))^{2} <F_X(x)=F_{X,Y}(x,x)$ provided $F_X(x)<1$.






          share|cite|improve this answer









          $endgroup$



          If $X=Y$ then $F_X(x)F_Y(x)=(F_X(x))^{2} <F_X(x)=F_{X,Y}(x,x)$ provided $F_X(x)<1$.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Mar 23 at 23:41









          Kavi Rama MurthyKavi Rama Murthy

          74.9k53270




          74.9k53270












          • $begingroup$
            For cases not perfectly dependent, is there a general rule of thumb?
            $endgroup$
            – user321627
            Mar 24 at 2:42










          • $begingroup$
            No. there is no reason to expect an inequalilty of the type you have come up with.
            $endgroup$
            – Kavi Rama Murthy
            Mar 24 at 4:55


















          • $begingroup$
            For cases not perfectly dependent, is there a general rule of thumb?
            $endgroup$
            – user321627
            Mar 24 at 2:42










          • $begingroup$
            No. there is no reason to expect an inequalilty of the type you have come up with.
            $endgroup$
            – Kavi Rama Murthy
            Mar 24 at 4:55
















          $begingroup$
          For cases not perfectly dependent, is there a general rule of thumb?
          $endgroup$
          – user321627
          Mar 24 at 2:42




          $begingroup$
          For cases not perfectly dependent, is there a general rule of thumb?
          $endgroup$
          – user321627
          Mar 24 at 2:42












          $begingroup$
          No. there is no reason to expect an inequalilty of the type you have come up with.
          $endgroup$
          – Kavi Rama Murthy
          Mar 24 at 4:55




          $begingroup$
          No. there is no reason to expect an inequalilty of the type you have come up with.
          $endgroup$
          – Kavi Rama Murthy
          Mar 24 at 4:55


















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