Turn on thread page Beta
    • Thread Starter
    Offline

    2
    ReputationRep:
    Now I have a question
    they stated that population variance is assumed to be the same as the sample one.

    but the markscheme uses the t-test because it says the sample size is small

    but is it wrong if I use the z test?

    Thanks~
    Attached Images
      
    Offline

    15
    ReputationRep:
    (Original post by akk713)
    Now I have a question
    they stated that population variance is assumed to be the same as the sample one.

    but the markscheme uses the t-test because it says the sample size is small

    but is it wrong if I use the z test?

    Thanks~
    the Normal distribution (Z test) should only be used as an approximation when the sample size is 30 or over, because it is a continuous distribution, and you will get a sampling error if you use it for small discrete values.
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by 4Ed)
    the Normal distribution (Z test) should only be used as an approximation when the sample size is 30 or over, because it is a continuous distribution, and you will get a sampling error if you use it for small discrete values.
    So I should use the t-test regardless whether I know the variance or not?
    I thought for any sample size, if the variance is known, you can still use the z test?!
    Offline

    15
    ReputationRep:
    (Original post by akk713)
    So I should use the t-test regardless whether I know the variance or not?
    I thought for any sample size, if the variance is known, you can still use the z test?!
    read http://mathworld.wolfram.com/Student...tribution.html for the definition of the t-test.
    if the sample is small and discrete, you can't model it using a normal distribution - but as the sample size increases, the student-t graph approximates to a normal distribution, and that's why it cant be used in this case... the sample size is too small.
 
 
 

University open days

  • University of Warwick
    Undergraduate Open Days Undergraduate
    Sat, 20 Oct '18
  • University of Sheffield
    Undergraduate Open Days Undergraduate
    Sat, 20 Oct '18
  • Edge Hill University
    Faculty of Health and Social Care Undergraduate
    Sat, 20 Oct '18
Poll
Who is most responsible for your success at university

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.