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Thread: Paired T Test ???

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    Paired T Test ???




    Hi

    I am trying to work out which statistical test to use to determine whether there is a relationship between visual acuity (how small letters on a letter chart are) and contrast (how dark the letters are). I have used one sample of participants and tested both visual acuity and contrast on each participant. Will a Paired T-test do this?

    Thanks

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    Re: Paired T Test ???

    For paired t-test, you need measurements on the same scale.
    What exactely do you mean by "relationship"? Maybe just a
    correlation? Which correlation coefficient would be feasable
    depends on how your variables were measured.

    With kind regards

    K.

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    Re: Paired T Test ???

    Thanks for your reply. I want to see if as visual acuity improves, contrast also improves.
    Sorry I am terrible at stats!!!

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    Re: Paired T Test ?

    If both variables were measured on an ->interval scale, then ->Pearson Correlation would be an option.
    If one both variables were measured on an ->ordinal scale, or sample size is small (n < 20), then ->Spearman's rank correlation would be an option.

    With kind regards

    K.

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    Re: Paired T Test ?

    Thank you Karabiner.

    I have carried out a Pearson Correlation (interval data, n=25) in Excel and it has come out with 0.179765513. Does this mean there is v little association between the 2?

    I then did a t-test and it comes out with 4.90562E-57. Does this mean there is a high probabillity of no association.

    Now I am even more confused?

    Thanks again

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    Re: Paired T Test ?


    unfortunately i don't understand what you presented as result of your t-test.
    But anyway, you did not ask whether the means of the two variables differ, so
    you do nor need a t-test. The degree of association between the two variables is represented by the correlation coefficient, which is indeed small in the sample
    (if it actually was the coefficient r and not the p- value).

    With Kind regards

    K.

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