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Thread: Epidemiological Stats: Accepting/Rejecting a Null Hypothesis

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    Epidemiological Stats: Accepting/Rejecting a Null Hypothesis




    Hello,
    I'm a grad student looking for help with what is probably a very simple question to someone with the right knowledge. I'm trying to finish my Master's research project which is a cross-sectional study examining prevalence of a disease within a local population. I've done all the descriptive statistics I need, but am I looking for the best inferential test(s) to accept or reject my null hypothesis and sub-hypotheses. I have 211 subjects who either test positive or negative for the disease, and I hypothesized that different sub-populations would be either negative or positive as well. Thus, some of the sample sizes are even smaller depending on the population being examined. I was told chi-square wouldn't work because of my small sample size? Could anyone tell me a better way to test this? (Hypotheses are that my data will reflect other current research results.)
    Thanks very much!

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    Re: Epidemiological Stats: Accepting/Rejecting a Null Hypothesis

    maybe a logistic regression would be of use here?
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    Re: Epidemiological Stats: Accepting/Rejecting a Null Hypothesis

    What kind of subgroups are you interested in? I.e. what are your independent variables? Will you be using any control variables?

    Quote Originally Posted by jack2013 View Post
    am I looking for the best inferential test(s) to accept or reject my null hypothesis and sub-hypotheses.
    Be careful with terminology. Conventional significance testing doesn't allow us to accept null hypotheses, only to reject them. A non-significant p value only means we haven't got enough evidence to reject the null. It doesn't mean that we have evidence to support or to accept it.

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    Re: Epidemiological Stats: Accepting/Rejecting a Null Hypothesis

    Yes, a non-significant p value only allows for rejection of the Ho.
    As far as logistical regression goes, this looks like it would work for me, because I have nominal data variables to be paired with other nominal/ordinal variables. Is it possible to run logistic regression or multiple logistic regression in excel? Is it very difficult?
    Thanks!

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    Re: Epidemiological Stats: Accepting/Rejecting a Null Hypothesis

    Quote Originally Posted by jack2013 View Post
    Yes, a non-significant p value only allows for rejection of the Ho.
    I think you just missed a word but to be clear: a non-significant p-value only allows you to fail to reject the null hypothesis (as opposed to reject it like you said).
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    Re: Epidemiological Stats: Accepting/Rejecting a Null Hypothesis

    Quote Originally Posted by jack2013 View Post
    Is it possible to run logistic regression or multiple logistic regression in excel?
    I'm not sure; you'd probably need some kind of add-in to do so. But it's probably best not to use Excel for serious data analysis (some reasons here).

    It would be easier and better to use a proper stats package or computing environment. E.g. R allows you to run a logistic regression very simply using code like this:

    Code: 
    glm(Y ~ X1 + X2 + X3, data = yourdata, family = "binomial")

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    Re: Epidemiological Stats: Accepting/Rejecting a Null Hypothesis


    hi,
    coming back to the original question, I wonder how the sample size is too low for chi-squared. If I remember correctly the rule of the thumb is 5 data points in each cell which does not seem difficult with your number of samples.

    Concerning the logistic regression, if you do not have continuous independent variables there should be no difference to a chi-squared I believe. If you do have continuous X-s then chis-squared is not an option at all.

    regards
    rogojel

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