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Thread: Comparing 2 groups with unequal number of samples + comparing multiple groups

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    Comparing 2 groups with unequal number of samples + comparing multiple groups




    Hello everyone, this is my first post here. I have been doing some surfing and reading on this forum and I must say, you guys are great.

    I am going to take a statistical course in the next couple of months, but unfortunately my questions cannot wait till then as I am analyzing my data now.

    Questions A:
    2 groups. Group 1: n = 180. Group 2: n= 25 (I think this can be classified as categorical, e.g. distribution of gender in each group).

    For this analysis I have used Chi Square. Do you agree? Since it is a 2x2 categorical data)

    Question B:
    5 groups.
    Group1: n = 178 (e.g. 170 +ve, 8 -ve)
    Group2: n= 15 (e.g 5 +ve, 10 -ve)
    Group3: n = 15
    Group4: n = 8
    Group5: n = 24

    Each group represent a test result, and we are comparing the test results to see if it correlate with the diagnosis.
    e.g. 5 ways of measuring blood glucose levels, we want to see if there are any difference between these groups.
    Can I use One way ANOVA?

    I very much appreciate the help.

    Thanks

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    Re: Comparing 2 groups with unequal number of samples + comparing multiple groups

    Question 1, yes this seems appropriate given your description. However you need to have at least 5 of each sex in both groups. Thus, if you put the data into a 2x2 table, gender by group, each cell needs at least 5 individuals.
    Stop cowardice, ban guns!

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    Re: Comparing 2 groups with unequal number of samples + comparing multiple groups

    You need to provide more information about the second question, such as, are these the same patients, and what your abbreviations represent.
    Stop cowardice, ban guns!

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    Re: Comparing 2 groups with unequal number of samples + comparing multiple groups

    For the second questions

    Lets say you have a test called Beta to diagnose Disease called "Q". Beta has 5 result possibilities; A, B, C, D and E.

    We have 230 patients tested using Beta. The following results were achieved.
    170 had a result of A, 25 had a result of B, 20 had a result of C, 8 had a result of D, and 7 had a result of E.

    Out of the 230 patients 160 were known to have the disease Q.

    Test result A: 155/160 have disease Q
    result B: 5/25
    result C: 2/20
    result D: 0/8
    result E: 1/7

    Can I use one way anova to show statistical difference between the groups?

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    Re: Comparing 2 groups with unequal number of samples + comparing multiple groups

    Quote Originally Posted by hlsmith View Post
    Question 1, yes this seems appropriate given your description. However you need to have at least 5 of each sex in both groups. Thus, if you put the data into a 2x2 table, gender by group, each cell needs at least 5 individuals.
    yes each cell in the 2x2 table has more than 5.

    what about T-test for question 1 would it be better?

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    Re: Comparing 2 groups with unequal number of samples + comparing multiple groups


    hi,
    you have discrete data so neither Anova nor the t test is appropriate as they are for continuous data. Chi-squared could work but you do not have enough values in the last 3 cells. Grouping C D and E into one category might work, but you still only have 3 data points instead of 5 in the grouped cell.

    I think Fishers exact test could work best for you
    http://udel.edu/~mcdonald/statfishers.html

    regards
    rogojel

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