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Math Help - Comparing means with a categorical dependent var & a continuous independent var

  1. #1
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    Comparing means with a categorical dependent var & a continuous independent var

    Hi,

    I want to compare the mean length of the growing season for populations that are increasing, decreasing and are stable. I simply want to determine whether the populations have the same mean length in growing season (1985-2006) or are they different. I know you would normally use ANOVA when you have a continuous dependent variable and a categorical variable.

    Thanks!
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  2. #2
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    Re: Comparing means with a categorical dependent var & a continuous independent var

    Your hypothesis, H_0: \mu_1 = \mu_2 =\mu_3 can be tested with a simple ANOVA. Just check the F value.
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    Re: Comparing means with a categorical dependent var & a continuous independent var

    But because my dependent variable (population status) is categorical, and my independent variable (length of growing season) is continuous I violate one of the assumptions of ANOVA (dependent = continuous & independent = categorical). How do I get around violating the assumption of ANOVA?
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  4. #4
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    Re: Comparing means with a categorical dependent var & a continuous independent var

    Three categorical variable possibilities: Increasing, decreasing, Stable. This is your dependent. Lets call it status.
    Length of growing season: Some number of days im presuming in that year im presuming ? Season
    On SAS
    PROC GLM Data=??;
    Class status;
    Season=status;
    run;
    I think you are backwards or something that is not an assumption of ANOVA.
    Last edited by Scopur; November 29th 2012 at 11:41 AM.
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  5. #5
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    Re: Comparing means with a categorical dependent var & a continuous independent var

    Yes, the three categorical possibilities: Increasing, Decreasing, Stable
    Dependent variable: Length of Growing Season (one julian day value for each year from 1895-2006)
    So there are 22 measures of the length of the growing season (one for each year) for each of the three categories increasing, decreasing and stable.
    Question: Is the mean length of growing season the same for increasing, decreasing and stable populations?
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  6. #6
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    Re: Comparing means with a categorical dependent var & a continuous independent var

    OHHH im sorry i thought that each year was either classified as a year of increasing deacreasing or stable. Not that each year contained all three of the growing seasons. Let me think for a minute...

    So i think you want to use a generalized linear model, probably a poisson with a log link function.
    Last edited by Scopur; November 29th 2012 at 12:01 PM.
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  7. #7
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    Re: Comparing means with a categorical dependent var & a continuous independent var

    One of the assumptions of ANOVA is that your dependent variable is continuous and independent variable is categorical correct?
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  8. #8
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    Re: Comparing means with a categorical dependent var & a continuous independent var

    No No you are right. For some reason i was getting independent and dependent variable backwards in my head. Any ways i think you have to use a GLM, multinomial or poisson regression model.
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  9. #9
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    Re: Comparing means with a categorical dependent var & a continuous independent var

    Any suggestions would be greatly appreciated! Need to get this solved fast!!
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