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Thread: Correct Use of Chi-Square?

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    Correct Use of Chi-Square?




    Hi all,

    I am trying to test whether one group is significantly different from another in two different collections of data. I have seen that people tend to use chi-squared or fisher's exact for this calculation, but am I doing it correctly? Here is the data:


    Group 1:

    WGD + SSD 19590 14184 72%
    WGD 19590 7045 36%
    SSD 19590 7139 36%
    Singleton 19590 5406 28%

    Group 2:

    WGD + SSD 110 102 93%
    WGD 110 75 68%
    SSD 110 27 25%
    Singleton 110 8 7%

    (The numbered columns are 1. Group total, 2. Category total 3. proportion.)

    If I want to, for example, check whether the number of WGD + SSD is significantly different in group 2 verses group 1, would I set up my contingency table like so?

    19590 110
    14184 102

    This returns a P value of 0.0839 using a two tailed Chi-square with Yates' correction, but the proportions are 93% versus 72%. Have I done something wrong here, or are the numbers in the second group too low compared to the first?

    Thanks in advance!

    EDIT: http://graphpad.com/quickcalcs/contingency1/ was used to carry out the test to get this p value
    Last edited by Ogtos; 08-14-2014 at 06:01 AM.

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