What variable is the conditional probability function a function of?












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I've got the following excerpt from my notes in my statistics course:



enter image description here



In the second line, the professor put $x=1$ in the Poisson distribution equation. My question, how do I know that the conditional distribution function is a function of $X_2$, and not $X_1$?










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  • $begingroup$
    No you can't. The conditional distribution function $X_2mid X_1$ is by defintion a function of $X_1$ and $X_2$.
    $endgroup$
    – GNUSupporter 8964民主女神 地下教會
    Dec 9 '18 at 20:46










  • $begingroup$
    @GNUSupporter8964民主女神地下教會: But then how can the professor have substituted 1 into the equation, if it's not a function of $X_2$?
    $endgroup$
    – The_Questioner
    Dec 9 '18 at 21:01










  • $begingroup$
    It's a function of both $X_1$ and $X_2$.
    $endgroup$
    – GNUSupporter 8964民主女神 地下教會
    Dec 9 '18 at 21:02










  • $begingroup$
    @GNUSupporter8964民主女神地下教會: But in the second line, he substituted, $P(X_2 = x_2 | X_1 = x_1)$ with $frac{e^{-k}k^1}{1!}$. So in the Poisson distribution, in the place of the variable $x$, he put $1$. So that means he made it a function of $X_2$, right?
    $endgroup$
    – The_Questioner
    Dec 9 '18 at 21:07










  • $begingroup$
    In your previous comment, I don't understand what $x$ is. $P(X_2 = x_2 | X_1 = x_1)$ is a function of $x_1$ and $x_2$.
    $endgroup$
    – GNUSupporter 8964民主女神 地下教會
    Dec 9 '18 at 21:15
















0












$begingroup$


I've got the following excerpt from my notes in my statistics course:



enter image description here



In the second line, the professor put $x=1$ in the Poisson distribution equation. My question, how do I know that the conditional distribution function is a function of $X_2$, and not $X_1$?










share|cite|improve this question









$endgroup$












  • $begingroup$
    No you can't. The conditional distribution function $X_2mid X_1$ is by defintion a function of $X_1$ and $X_2$.
    $endgroup$
    – GNUSupporter 8964民主女神 地下教會
    Dec 9 '18 at 20:46










  • $begingroup$
    @GNUSupporter8964民主女神地下教會: But then how can the professor have substituted 1 into the equation, if it's not a function of $X_2$?
    $endgroup$
    – The_Questioner
    Dec 9 '18 at 21:01










  • $begingroup$
    It's a function of both $X_1$ and $X_2$.
    $endgroup$
    – GNUSupporter 8964民主女神 地下教會
    Dec 9 '18 at 21:02










  • $begingroup$
    @GNUSupporter8964民主女神地下教會: But in the second line, he substituted, $P(X_2 = x_2 | X_1 = x_1)$ with $frac{e^{-k}k^1}{1!}$. So in the Poisson distribution, in the place of the variable $x$, he put $1$. So that means he made it a function of $X_2$, right?
    $endgroup$
    – The_Questioner
    Dec 9 '18 at 21:07










  • $begingroup$
    In your previous comment, I don't understand what $x$ is. $P(X_2 = x_2 | X_1 = x_1)$ is a function of $x_1$ and $x_2$.
    $endgroup$
    – GNUSupporter 8964民主女神 地下教會
    Dec 9 '18 at 21:15














0












0








0





$begingroup$


I've got the following excerpt from my notes in my statistics course:



enter image description here



In the second line, the professor put $x=1$ in the Poisson distribution equation. My question, how do I know that the conditional distribution function is a function of $X_2$, and not $X_1$?










share|cite|improve this question









$endgroup$




I've got the following excerpt from my notes in my statistics course:



enter image description here



In the second line, the professor put $x=1$ in the Poisson distribution equation. My question, how do I know that the conditional distribution function is a function of $X_2$, and not $X_1$?







probability statistics conditional-probability






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share|cite|improve this question











share|cite|improve this question




share|cite|improve this question










asked Dec 9 '18 at 20:44









The_QuestionerThe_Questioner

4771514




4771514












  • $begingroup$
    No you can't. The conditional distribution function $X_2mid X_1$ is by defintion a function of $X_1$ and $X_2$.
    $endgroup$
    – GNUSupporter 8964民主女神 地下教會
    Dec 9 '18 at 20:46










  • $begingroup$
    @GNUSupporter8964民主女神地下教會: But then how can the professor have substituted 1 into the equation, if it's not a function of $X_2$?
    $endgroup$
    – The_Questioner
    Dec 9 '18 at 21:01










  • $begingroup$
    It's a function of both $X_1$ and $X_2$.
    $endgroup$
    – GNUSupporter 8964民主女神 地下教會
    Dec 9 '18 at 21:02










  • $begingroup$
    @GNUSupporter8964民主女神地下教會: But in the second line, he substituted, $P(X_2 = x_2 | X_1 = x_1)$ with $frac{e^{-k}k^1}{1!}$. So in the Poisson distribution, in the place of the variable $x$, he put $1$. So that means he made it a function of $X_2$, right?
    $endgroup$
    – The_Questioner
    Dec 9 '18 at 21:07










  • $begingroup$
    In your previous comment, I don't understand what $x$ is. $P(X_2 = x_2 | X_1 = x_1)$ is a function of $x_1$ and $x_2$.
    $endgroup$
    – GNUSupporter 8964民主女神 地下教會
    Dec 9 '18 at 21:15


















  • $begingroup$
    No you can't. The conditional distribution function $X_2mid X_1$ is by defintion a function of $X_1$ and $X_2$.
    $endgroup$
    – GNUSupporter 8964民主女神 地下教會
    Dec 9 '18 at 20:46










  • $begingroup$
    @GNUSupporter8964民主女神地下教會: But then how can the professor have substituted 1 into the equation, if it's not a function of $X_2$?
    $endgroup$
    – The_Questioner
    Dec 9 '18 at 21:01










  • $begingroup$
    It's a function of both $X_1$ and $X_2$.
    $endgroup$
    – GNUSupporter 8964民主女神 地下教會
    Dec 9 '18 at 21:02










  • $begingroup$
    @GNUSupporter8964民主女神地下教會: But in the second line, he substituted, $P(X_2 = x_2 | X_1 = x_1)$ with $frac{e^{-k}k^1}{1!}$. So in the Poisson distribution, in the place of the variable $x$, he put $1$. So that means he made it a function of $X_2$, right?
    $endgroup$
    – The_Questioner
    Dec 9 '18 at 21:07










  • $begingroup$
    In your previous comment, I don't understand what $x$ is. $P(X_2 = x_2 | X_1 = x_1)$ is a function of $x_1$ and $x_2$.
    $endgroup$
    – GNUSupporter 8964民主女神 地下教會
    Dec 9 '18 at 21:15
















$begingroup$
No you can't. The conditional distribution function $X_2mid X_1$ is by defintion a function of $X_1$ and $X_2$.
$endgroup$
– GNUSupporter 8964民主女神 地下教會
Dec 9 '18 at 20:46




$begingroup$
No you can't. The conditional distribution function $X_2mid X_1$ is by defintion a function of $X_1$ and $X_2$.
$endgroup$
– GNUSupporter 8964民主女神 地下教會
Dec 9 '18 at 20:46












$begingroup$
@GNUSupporter8964民主女神地下教會: But then how can the professor have substituted 1 into the equation, if it's not a function of $X_2$?
$endgroup$
– The_Questioner
Dec 9 '18 at 21:01




$begingroup$
@GNUSupporter8964民主女神地下教會: But then how can the professor have substituted 1 into the equation, if it's not a function of $X_2$?
$endgroup$
– The_Questioner
Dec 9 '18 at 21:01












$begingroup$
It's a function of both $X_1$ and $X_2$.
$endgroup$
– GNUSupporter 8964民主女神 地下教會
Dec 9 '18 at 21:02




$begingroup$
It's a function of both $X_1$ and $X_2$.
$endgroup$
– GNUSupporter 8964民主女神 地下教會
Dec 9 '18 at 21:02












$begingroup$
@GNUSupporter8964民主女神地下教會: But in the second line, he substituted, $P(X_2 = x_2 | X_1 = x_1)$ with $frac{e^{-k}k^1}{1!}$. So in the Poisson distribution, in the place of the variable $x$, he put $1$. So that means he made it a function of $X_2$, right?
$endgroup$
– The_Questioner
Dec 9 '18 at 21:07




$begingroup$
@GNUSupporter8964民主女神地下教會: But in the second line, he substituted, $P(X_2 = x_2 | X_1 = x_1)$ with $frac{e^{-k}k^1}{1!}$. So in the Poisson distribution, in the place of the variable $x$, he put $1$. So that means he made it a function of $X_2$, right?
$endgroup$
– The_Questioner
Dec 9 '18 at 21:07












$begingroup$
In your previous comment, I don't understand what $x$ is. $P(X_2 = x_2 | X_1 = x_1)$ is a function of $x_1$ and $x_2$.
$endgroup$
– GNUSupporter 8964民主女神 地下教會
Dec 9 '18 at 21:15




$begingroup$
In your previous comment, I don't understand what $x$ is. $P(X_2 = x_2 | X_1 = x_1)$ is a function of $x_1$ and $x_2$.
$endgroup$
– GNUSupporter 8964民主女神 地下教會
Dec 9 '18 at 21:15










1 Answer
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$begingroup$

You are given that
$$
P(X_2 = j | X_1 = k) =
e^{-k} frac{k^j}{j!}
$$
for any nonnegative integers $j, k$. Now just plug in $j=1$ to obtain
$$
P(X_2 = 1 | X_1 = k) =
e^{-k} frac{k^1}{1!}.
$$






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    1 Answer
    1






    active

    oldest

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    1 Answer
    1






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    0












    $begingroup$

    You are given that
    $$
    P(X_2 = j | X_1 = k) =
    e^{-k} frac{k^j}{j!}
    $$
    for any nonnegative integers $j, k$. Now just plug in $j=1$ to obtain
    $$
    P(X_2 = 1 | X_1 = k) =
    e^{-k} frac{k^1}{1!}.
    $$






    share|cite|improve this answer









    $endgroup$


















      0












      $begingroup$

      You are given that
      $$
      P(X_2 = j | X_1 = k) =
      e^{-k} frac{k^j}{j!}
      $$
      for any nonnegative integers $j, k$. Now just plug in $j=1$ to obtain
      $$
      P(X_2 = 1 | X_1 = k) =
      e^{-k} frac{k^1}{1!}.
      $$






      share|cite|improve this answer









      $endgroup$
















        0












        0








        0





        $begingroup$

        You are given that
        $$
        P(X_2 = j | X_1 = k) =
        e^{-k} frac{k^j}{j!}
        $$
        for any nonnegative integers $j, k$. Now just plug in $j=1$ to obtain
        $$
        P(X_2 = 1 | X_1 = k) =
        e^{-k} frac{k^1}{1!}.
        $$






        share|cite|improve this answer









        $endgroup$



        You are given that
        $$
        P(X_2 = j | X_1 = k) =
        e^{-k} frac{k^j}{j!}
        $$
        for any nonnegative integers $j, k$. Now just plug in $j=1$ to obtain
        $$
        P(X_2 = 1 | X_1 = k) =
        e^{-k} frac{k^1}{1!}.
        $$







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Dec 10 '18 at 0:52









        littleOlittleO

        29.7k646109




        29.7k646109






























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