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    Total complications in both groups




    Hi,

    I have the following question:

    In my study I compare two kinds of surgery options. Group A has 9 patients and group B has 6 patients. When comparing the seperate complications there is no significant difference. But now I want to compare the total of complications between group A and group B.

    Group A (9 pt): total 11 complications in 6 patients (3 patients had no complications
    Group B (6 pt): total 2 complications, both in the same patient (5 patients had no complication)

    Which test suits my question best?

    Thanks

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    Re: Total complications in both groups

    Are you saying you want to collapse all complication types to create a composite outcome. Say, any outcome (y/n; e.g., site infection, readmission, rejection, etc.)?
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    Re: Total complications in both groups

    I want to compare the total amount of complications between group A (9 patients) en group B (6 patients) (11 vs 2 complications) and see if there is a significant difference.

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    Re: Total complications in both groups

    Check out Fisher's exact test.

    Side note, you will have limited generalizability of results if the intervention was not randomized.
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    Re: Total complications in both groups

    Quote Originally Posted by chabby View Post
    Which test suits my question best?
    Hi Chabby,

    Count data is typically best examined through a Poisson model. If there are any differences between patients regarding length of time during which a complication could be observed, this can also be handled via the model offset. I don't believe you have to worry about that in your case, though. So that should help simplify things. Alternatively, you could compare groups via a non-parametric test such as Kruskal-Wallis or Mann-Whitney and report median (1st, 3rd quartiles). A third alternative is to do a two-sample Student's t-test and report mean +/- standard deviation. These 3 ways are listed in the order that I recommend. If you aren't comfortable with the Poisson method, then I would say go with the non-parametric approach. However, as hlsmith indicates, if there are differences between groups, it can confound your results. A Poisson model could help adjust for differences.

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    Re: Total complications in both groups

    I must not have read the fine details. Mostater is correct in proposing a Poisson model. That would be my first choice as well.

    However the OP may be limited in their modeling and controlling for other covariates, given the very small sample size.
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    Re: Total complications in both groups

    Thanks for all the help, but I'm still not finished asking.

    One of my teachers recommends the following:
    Every complication is one patient and then make a cross-tab.

    With the next information:
    Group A (9 pt): total 11 complications in 6 patients (3 patients had no complications
    Group B (6 pt): total 2 complications, both in the same patient (5 patients had no complication)

    You will get this cross-tab:

    Group A Group B
    Complication 11 2
    No complication 3 5

    He mentioned just to run a fisher's exact test then.

    But I thought this would not be allowed.

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    Re: Total complications in both groups

    If I were you, I would categorise patientsinto having 1 or more complications or no complications at all; then you should be able to do Fishers.

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    Re: Total complications in both groups

    Quote Originally Posted by chabby View Post
    He mentioned just to run a fisher's exact test then.

    But I thought this would not be allowed.
    When comparing frequencies between groups as you just described, Fisher's is perfectly allowed. This is different than comparing # of complications between groups. Now you are comparing # of patients having complications between groups. So use Fisher's for that analysis.

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    Re: Total complications in both groups


    You will have to modify your previous numbers for using the Fisher's Test:


    lllllllllllllllllllComplication(s) No Complication
    Group A.......... 6.................3
    Group B...........1................ 5
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