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    Is this possible?




    Hi,

    I have come stuck on a really simple question. I have access to excel and SPSS.

    I have a dataset of response to a treatment. Sample size = 40. 30 responded and 10 did not. As it was a novel approach patients were not expected to respond ie. null = treatment does not lead to response.

    Can I work out a p value from just this? If so how.

    Sorry if it's very basic but would really value any help.

    Thanks,

    K
    Last edited by k093; 08-27-2014 at 11:10 PM.

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    Re: Is this possible?

    Is the following valid simple chi squared valid for this situation as follows?

    Response
    Observed N Expected N Residual
    .00 10 20.0 -10.0
    1.00 30 20.0 10.0
    Total 40

    Test Statistics
    Response
    Chi-Square 10.000a
    df 1
    Asymp. Sig. .002
    a 0 cells (0.0%) have expected frequencies less than 5. The minimum expected cell frequency is 20.0.


    Therefore p value 0.002 ?

    I am a little confused should our expected value for "0 response" not be 40?

    Thanks

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    Re: Is this possible?

    You need to provide more detail to your question. 40 people, 30 had a change, 10 did not, no control group, correct?
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    k093 (08-28-2014)

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    Re: Is this possible?

    Thanks for the reply. Unfortunately there is no control group - not ideal I know but it just represents preliminary work.

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    Re: Is this possible?

    Unless, you had a null hypothesis with a suspected % response, there really is no statistic for you. How did you define/quantify response, perhaps you can look at differences in values.
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    Re: Is this possible?

    I thought that may be the case. Response was defined as resolution of symptoms as reported by patient and/or a 20% drop in a blood test value. Would wilcoxon rank rum for change in blood test value between responders and non responders be reasonable ?
    Last edited by k093; 08-28-2014 at 09:10 AM.

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    Re: Is this possible?

    If you have those valules for all patients in both groups, you can calculate difference and use Wilcoxon sign test (analog to paired t-test).
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    Re: Is this possible?


    Quote Originally Posted by k093 View Post
    I thought that may be the case. Response was defined as resolution of symptoms as reported by patient and/or a 20% drop in a blood test value. Would wilcoxon rank rum for change in blood test value between responders and non responders be reasonable ?
    First you use blood test as a means to define responder and
    non-responder, and the you look at whether responders and
    non-responders differ with regard to blood test? Does not
    sound too useful.

    As to your first question: why do you think you need a p-value?
    p-values ar means to an end, they help to decide whether
    to maintain the Null hypothesis or reject the Null hypothesis.

    Since you have at least 1 responder in your sample, the Null
    hypothesis that in the population the response rate is exactely
    = 0.00000% can safely be rejected.

    As mentioned above by hlsmith, only some other expected
    response rate (different from 0%) could be sensibly tested.

    With kind regards

    K.

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