Results 1 to 2 of 2

Math Help - joint and marginal PMF's

  1. #1
    Member
    Joined
    Mar 2010
    Posts
    122

    joint and marginal PMF's

    X
    -1 0 1
    -1 0 0 (1/3)
    Y 0 0 (1/3) 0
    1 (1/3) 0 0

    Now for this i am pretty sure my calculations are correct but i want to check because there seems to be some errors in the textxbook which confused me.

    for the marginal PMF say of x, i simply thought i simply sum the coresponding column.
    For example p{-1)=1/3
    p(0)=1/3
    p(1)=1/3

    But when they do this in the book the value they obtain does not corespond to the sum of the column they are refering to, and this happens twice, and i dont think there would be two errors in the same question and hence i'm a bit confused now.

    Next part to find E[XY] i multiply all values of x and y which gives me XY=-1,0,1, with corresponding probabilities.

    Then to check if these random variables are independendant i check if E[XY]=E[x]E[Y]
    which in this case is zero. so they must be independant. Can someone tell me if i am doing something wrong.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor matheagle's Avatar
    Joined
    Feb 2009
    Posts
    2,763
    Thanks
    5
    I don't understand your distribution.

    Why not just write P(X=0,Y=0)=... you only seem to have 3 points.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Joint and marginal distributions
    Posted in the Advanced Statistics Forum
    Replies: 4
    Last Post: July 26th 2011, 08:52 AM
  2. Marginal and joint pdf
    Posted in the Advanced Statistics Forum
    Replies: 1
    Last Post: May 10th 2010, 05:44 PM
  3. Marginal PDF from Joint PDF?
    Posted in the Statistics Forum
    Replies: 6
    Last Post: February 19th 2010, 12:59 AM
  4. joint / marginal pdf
    Posted in the Advanced Statistics Forum
    Replies: 7
    Last Post: May 27th 2009, 05:48 PM
  5. joint and marginal p.m.f.s
    Posted in the Advanced Statistics Forum
    Replies: 5
    Last Post: May 20th 2009, 08:24 PM

Search Tags


/mathhelpforum @mathhelpforum