+ Reply to Thread
Results 1 to 4 of 4

Thread: Statistics homework

  1. #1
    Points: 108, Level: 2
    Level completed: 16%, Points required for next Level: 42

    Posts
    3
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Statistics homework




    Hello, I am doing an introductional statistics unit in my first semester at uni the moment. I have a question to do and I have tried it for several days, but I still did not solve it.

    I have to derive a marginal distribution function for X. X is defined as the sum of N independent Bernoulli trials. N is a random variable that behaves according to a Poisson distribution. p, Lambda etc is not given, so I have to derive a general function.

    Thanks for your help
    Attached Images  

  2. #2
    TS Contributor
    Points: 22,410, Level: 93
    Level completed: 6%, Points required for next Level: 940

    Posts
    3,020
    Thanks
    12
    Thanked 565 Times in 537 Posts

    Re: Statistics homework

    Have not check your whole calculation, but one reminder for you from the first line:

    You have correctly stated that n \geq x in the summation, as required in a Binomial model. Note that you are calculating the pmf

    \Pr\{X = x\}

    and from the whole calculation process x is fixed from the very beginning. (And if this calculation results holds for all support point of X, then you have finished calculating the whole pmf of X)

    For each fixed x, we have

    \Pr\{N = n, X = x\} = 0 when n < x

    Therefore all the initial terms from n = 0 to n = x - 1 vanished, and you are actually summing from n = x.

  3. #3
    Points: 108, Level: 2
    Level completed: 16%, Points required for next Level: 42

    Posts
    3
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Re: Statistics homework

    Oh thank you, you are absolutely right

  4. #4
    Points: 108, Level: 2
    Level completed: 16%, Points required for next Level: 42

    Posts
    3
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Re: Statistics homework


    Nobody has any advice?

+ Reply to Thread

           




Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts






Advertise on Talk Stats