+ Reply to Thread
Results 1 to 3 of 3

Thread: large cell counts - Fisher's Exact vs. chi2

  1. #1
    Points: 19, Level: 1
    Level completed: 37%, Points required for next Level: 31

    Posts
    2
    Thanks
    0
    Thanked 0 Times in 0 Posts

    large cell counts - Fisher's Exact vs. chi2




    Hi everyone,
    I read a while back that chi2 was most accurate for observed cell counts of only between 5-70, but now I can't find that reference. I'm wondering if anyone can point me in the right direction. I have samples of 450-650 and have used Fisher's Exact as a result of having observed cell counts over 70. I'm looking to justify this approach with a source. Any help would be appreciated.
    Thanks!

  2. #2
    Omega Contributor
    Points: 38,253, Level: 100
    Level completed: 0%, Points required for next Level: 0
    hlsmith's Avatar
    Location
    Not Ames, IA
    Posts
    6,989
    Thanks
    397
    Thanked 1,185 Times in 1,146 Posts

    Re: large cell counts - Fisher's Exact vs. chi2

    You should always use Fisher's test, given that it will run in a timely fashion. It has factorials and big numbers in it, so it can take awhile some times when you have large counts.
    Stop cowardice, ban guns!

  3. #3
    Points: 19, Level: 1
    Level completed: 37%, Points required for next Level: 31

    Posts
    2
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Question Re: large cell counts - Fisher's Exact vs. chi2


    There is a lot of received wisdom around non-parametric tests, particularly those relating to 2x2 contingency tables with the unquestioned assumption being that unless the expected cell count is <5, one must use chi2. Unfortunately, I'm stuck in such a position of needing to prove chi2 is not the best test. Do you have a source regarding Exact tests always being better than estimated p? Thanks!

+ Reply to Thread

           




Tags for this 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