What is the name of this formula derived from the Poisson distribution?












4












$begingroup$


I am learning about the Poisson distribution in this document and its link reference.



This is the key formula to compute the Poisson distribution:



$$
f(k; lambda)=frac{lambda^k e^{-lambda}}{k!}
$$



I saw another related formula somewhere.



$$
sumlimits_{k = x}^{+ infty}
frac{lambda^k e^{-lambda}}{k!}
$$



Is there a name for this formula?










share|cite|improve this question











$endgroup$

















    4












    $begingroup$


    I am learning about the Poisson distribution in this document and its link reference.



    This is the key formula to compute the Poisson distribution:



    $$
    f(k; lambda)=frac{lambda^k e^{-lambda}}{k!}
    $$



    I saw another related formula somewhere.



    $$
    sumlimits_{k = x}^{+ infty}
    frac{lambda^k e^{-lambda}}{k!}
    $$



    Is there a name for this formula?










    share|cite|improve this question











    $endgroup$















      4












      4








      4





      $begingroup$


      I am learning about the Poisson distribution in this document and its link reference.



      This is the key formula to compute the Poisson distribution:



      $$
      f(k; lambda)=frac{lambda^k e^{-lambda}}{k!}
      $$



      I saw another related formula somewhere.



      $$
      sumlimits_{k = x}^{+ infty}
      frac{lambda^k e^{-lambda}}{k!}
      $$



      Is there a name for this formula?










      share|cite|improve this question











      $endgroup$




      I am learning about the Poisson distribution in this document and its link reference.



      This is the key formula to compute the Poisson distribution:



      $$
      f(k; lambda)=frac{lambda^k e^{-lambda}}{k!}
      $$



      I saw another related formula somewhere.



      $$
      sumlimits_{k = x}^{+ infty}
      frac{lambda^k e^{-lambda}}{k!}
      $$



      Is there a name for this formula?







      probability






      share|cite|improve this question















      share|cite|improve this question













      share|cite|improve this question




      share|cite|improve this question








      edited Mar 22 at 0:42









      Peter Mortensen

      565310




      565310










      asked Mar 21 at 6:50









      shiqangpanshiqangpan

      152




      152






















          4 Answers
          4






          active

          oldest

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          6












          $begingroup$

          The first formula is the probability mass function (PMF) of the Poisson distribution and the second one is the survival function of this distribution. The first one gives you the probability that the Poisson random variable (which can take integer values) will equal $k$ and the second one the probability that it will be greater than or equal to $k$.






          share|cite|improve this answer









          $endgroup$





















            3












            $begingroup$

            The Taylor series for the function $g(lambda) = e^lambda$ is
            $$e^lambda = sum_{k=0}^infty frac{lambda^k}{k!}.$$
            By rearranging, you can verify that the sum of the probabilities of all outcomes for a Poisson($lambda$) random variable $X$ is $1$.
            $$sum_{k=0}^infty P(X = k) = sum_{k=0}^infty e^{-lambda} frac{lambda^k}{k!} = 1.$$






            share|cite|improve this answer









            $endgroup$





















              3












              $begingroup$

              To add on the answers by angryavian and Rohit Pandey, the complementary of the second formula is also the cumulative distribution function (CDF):
              $$ F(x-1) = P(X leq x-1) = sum_{k = 0}^{x-1}
              frac{lambda^k e^{-lambda}}{k!} = 1 - sum_{k = x}^{+ infty}
              frac{lambda^k e^{-lambda}}{k!}
              .
              $$






              share|cite|improve this answer









              $endgroup$





















                1












                $begingroup$

                To add on the answers by angryavian, Rohit Pandey and Ertxiem, the second formula is the complement of the CDF of Poisson PMF for "x-1"



                $$
                1 - F(x-1) =
                sum_{k = x}^{+ infty}
                frac{lambda^k e^{-lambda}}{k!}
                $$



                which means the probability of at least $x$ observations






                share|cite|improve this answer









                $endgroup$














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                  4 Answers
                  4






                  active

                  oldest

                  votes








                  4 Answers
                  4






                  active

                  oldest

                  votes









                  active

                  oldest

                  votes






                  active

                  oldest

                  votes









                  6












                  $begingroup$

                  The first formula is the probability mass function (PMF) of the Poisson distribution and the second one is the survival function of this distribution. The first one gives you the probability that the Poisson random variable (which can take integer values) will equal $k$ and the second one the probability that it will be greater than or equal to $k$.






                  share|cite|improve this answer









                  $endgroup$


















                    6












                    $begingroup$

                    The first formula is the probability mass function (PMF) of the Poisson distribution and the second one is the survival function of this distribution. The first one gives you the probability that the Poisson random variable (which can take integer values) will equal $k$ and the second one the probability that it will be greater than or equal to $k$.






                    share|cite|improve this answer









                    $endgroup$
















                      6












                      6








                      6





                      $begingroup$

                      The first formula is the probability mass function (PMF) of the Poisson distribution and the second one is the survival function of this distribution. The first one gives you the probability that the Poisson random variable (which can take integer values) will equal $k$ and the second one the probability that it will be greater than or equal to $k$.






                      share|cite|improve this answer









                      $endgroup$



                      The first formula is the probability mass function (PMF) of the Poisson distribution and the second one is the survival function of this distribution. The first one gives you the probability that the Poisson random variable (which can take integer values) will equal $k$ and the second one the probability that it will be greater than or equal to $k$.







                      share|cite|improve this answer












                      share|cite|improve this answer



                      share|cite|improve this answer










                      answered Mar 21 at 6:56









                      Rohit PandeyRohit Pandey

                      1,6581024




                      1,6581024























                          3












                          $begingroup$

                          The Taylor series for the function $g(lambda) = e^lambda$ is
                          $$e^lambda = sum_{k=0}^infty frac{lambda^k}{k!}.$$
                          By rearranging, you can verify that the sum of the probabilities of all outcomes for a Poisson($lambda$) random variable $X$ is $1$.
                          $$sum_{k=0}^infty P(X = k) = sum_{k=0}^infty e^{-lambda} frac{lambda^k}{k!} = 1.$$






                          share|cite|improve this answer









                          $endgroup$


















                            3












                            $begingroup$

                            The Taylor series for the function $g(lambda) = e^lambda$ is
                            $$e^lambda = sum_{k=0}^infty frac{lambda^k}{k!}.$$
                            By rearranging, you can verify that the sum of the probabilities of all outcomes for a Poisson($lambda$) random variable $X$ is $1$.
                            $$sum_{k=0}^infty P(X = k) = sum_{k=0}^infty e^{-lambda} frac{lambda^k}{k!} = 1.$$






                            share|cite|improve this answer









                            $endgroup$
















                              3












                              3








                              3





                              $begingroup$

                              The Taylor series for the function $g(lambda) = e^lambda$ is
                              $$e^lambda = sum_{k=0}^infty frac{lambda^k}{k!}.$$
                              By rearranging, you can verify that the sum of the probabilities of all outcomes for a Poisson($lambda$) random variable $X$ is $1$.
                              $$sum_{k=0}^infty P(X = k) = sum_{k=0}^infty e^{-lambda} frac{lambda^k}{k!} = 1.$$






                              share|cite|improve this answer









                              $endgroup$



                              The Taylor series for the function $g(lambda) = e^lambda$ is
                              $$e^lambda = sum_{k=0}^infty frac{lambda^k}{k!}.$$
                              By rearranging, you can verify that the sum of the probabilities of all outcomes for a Poisson($lambda$) random variable $X$ is $1$.
                              $$sum_{k=0}^infty P(X = k) = sum_{k=0}^infty e^{-lambda} frac{lambda^k}{k!} = 1.$$







                              share|cite|improve this answer












                              share|cite|improve this answer



                              share|cite|improve this answer










                              answered Mar 21 at 6:55









                              angryavianangryavian

                              42.5k23481




                              42.5k23481























                                  3












                                  $begingroup$

                                  To add on the answers by angryavian and Rohit Pandey, the complementary of the second formula is also the cumulative distribution function (CDF):
                                  $$ F(x-1) = P(X leq x-1) = sum_{k = 0}^{x-1}
                                  frac{lambda^k e^{-lambda}}{k!} = 1 - sum_{k = x}^{+ infty}
                                  frac{lambda^k e^{-lambda}}{k!}
                                  .
                                  $$






                                  share|cite|improve this answer









                                  $endgroup$


















                                    3












                                    $begingroup$

                                    To add on the answers by angryavian and Rohit Pandey, the complementary of the second formula is also the cumulative distribution function (CDF):
                                    $$ F(x-1) = P(X leq x-1) = sum_{k = 0}^{x-1}
                                    frac{lambda^k e^{-lambda}}{k!} = 1 - sum_{k = x}^{+ infty}
                                    frac{lambda^k e^{-lambda}}{k!}
                                    .
                                    $$






                                    share|cite|improve this answer









                                    $endgroup$
















                                      3












                                      3








                                      3





                                      $begingroup$

                                      To add on the answers by angryavian and Rohit Pandey, the complementary of the second formula is also the cumulative distribution function (CDF):
                                      $$ F(x-1) = P(X leq x-1) = sum_{k = 0}^{x-1}
                                      frac{lambda^k e^{-lambda}}{k!} = 1 - sum_{k = x}^{+ infty}
                                      frac{lambda^k e^{-lambda}}{k!}
                                      .
                                      $$






                                      share|cite|improve this answer









                                      $endgroup$



                                      To add on the answers by angryavian and Rohit Pandey, the complementary of the second formula is also the cumulative distribution function (CDF):
                                      $$ F(x-1) = P(X leq x-1) = sum_{k = 0}^{x-1}
                                      frac{lambda^k e^{-lambda}}{k!} = 1 - sum_{k = x}^{+ infty}
                                      frac{lambda^k e^{-lambda}}{k!}
                                      .
                                      $$







                                      share|cite|improve this answer












                                      share|cite|improve this answer



                                      share|cite|improve this answer










                                      answered Mar 21 at 7:07









                                      ErtxiemErtxiem

                                      60112




                                      60112























                                          1












                                          $begingroup$

                                          To add on the answers by angryavian, Rohit Pandey and Ertxiem, the second formula is the complement of the CDF of Poisson PMF for "x-1"



                                          $$
                                          1 - F(x-1) =
                                          sum_{k = x}^{+ infty}
                                          frac{lambda^k e^{-lambda}}{k!}
                                          $$



                                          which means the probability of at least $x$ observations






                                          share|cite|improve this answer









                                          $endgroup$


















                                            1












                                            $begingroup$

                                            To add on the answers by angryavian, Rohit Pandey and Ertxiem, the second formula is the complement of the CDF of Poisson PMF for "x-1"



                                            $$
                                            1 - F(x-1) =
                                            sum_{k = x}^{+ infty}
                                            frac{lambda^k e^{-lambda}}{k!}
                                            $$



                                            which means the probability of at least $x$ observations






                                            share|cite|improve this answer









                                            $endgroup$
















                                              1












                                              1








                                              1





                                              $begingroup$

                                              To add on the answers by angryavian, Rohit Pandey and Ertxiem, the second formula is the complement of the CDF of Poisson PMF for "x-1"



                                              $$
                                              1 - F(x-1) =
                                              sum_{k = x}^{+ infty}
                                              frac{lambda^k e^{-lambda}}{k!}
                                              $$



                                              which means the probability of at least $x$ observations






                                              share|cite|improve this answer









                                              $endgroup$



                                              To add on the answers by angryavian, Rohit Pandey and Ertxiem, the second formula is the complement of the CDF of Poisson PMF for "x-1"



                                              $$
                                              1 - F(x-1) =
                                              sum_{k = x}^{+ infty}
                                              frac{lambda^k e^{-lambda}}{k!}
                                              $$



                                              which means the probability of at least $x$ observations







                                              share|cite|improve this answer












                                              share|cite|improve this answer



                                              share|cite|improve this answer










                                              answered Mar 21 at 7:45









                                              YongYong

                                              111




                                              111






























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