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what to use? t-test or z-test?

Six Sigma – iSixSigma Forums Old Forums General what to use? t-test or z-test?

Viewing 7 posts - 1 through 7 (of 7 total)
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  • #48882

    Marona Aian
    Participant

    I was just confused about this one. I encountered a problem where 1 sample is greater than 30 and the other sample is less than 30. I do not know if i will use z-test or t-test. What test will I use?

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    #165925

    Six Sigma guy
    Member

    T test. Refer to the earlier post on the same topic

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    #165929

    Marona Aian
    Participant

    thank you sir for your kind reply. I wasn’t able to see that post earlier. thanks for the information.

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    #183629

    Srey
    Member

    z-test = greater than 30
    t-test = less than 30

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    #183632

    cobb
    Participant

    SreyWrong !

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    #183639

    Michael Mead
    Participant

    When in doubt, I suggest using the t-test. It is more conservative than the z-test and as the sample size gets bigger it approaches the z-test anyway.
    Textbooks recommend using the t-test when the sample size is less than 30. But, why is 30 a magic number?

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    #188497

    Zulfi
    Member

    add the samples.
    example: sample of 45 and 50
    where S would become 95

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