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    likelihood ratio test and AIC




    Can somebody please help me answer the question in the attachment. I have a test next week. please help
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    Re: likelihood ratio test and AIC

    So this is what I've done so far,

    for likelihood ratio
    model 1:
    (Lo+94.27)/Lo

    model 2:
    (Lo+90.83)/Lo

    Lo in the two models are equal, so model 2 is better. (model 2 < model 1)


    for AIC:
    model 1:
    2 *(94.27-5)=178.54

    model 2:
    2*(90.83-8)=165.66

    so model 2 better.


    is this correct?

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    Re: likelihood ratio test and AIC

    A likelihood ratio test isn't just seeing which likelihood is greater. The full model (model 2) is guaranteed to have a bigger likelihood. You need to do an actual statistical test.

    For the AIC calculation you need to be more careful with the signs. Note that your log likelihoods are negative. You can't just ignore that. Also the fact that your AICs don't match the given AICs should hint to you that maybe you messed up the calculation somewhat.
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    Re: likelihood ratio test and AIC

    Quote Originally Posted by Dason View Post
    A likelihood ratio test isn't just seeing which likelihood is greater. The full model (model 2) is guaranteed to have a bigger likelihood. You need to do an actual statistical test.

    For the AIC calculation you need to be more careful with the signs. Note that your log likelihoods are negative. You can't just ignore that. Also the fact that your AICs don't match the given AICs should hint to you that maybe you messed up the calculation somewhat.

    What kind of tests do you mean because what we have learned is

    if D1<D2 then model 1 better
    D=(Lo-Lm)/Lo


    ohh yes. The signs. Thank you for pointing that out. I didn't pay attention.

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    Re: likelihood ratio test and AIC

    Google likelihood ratio test. Then note that there is more to it than just looking at the values and seeing which one is 'better'. Like I said the likelihood for the full model will always be "better" so just comparing directly doesn't really tell us anything. You need to do an actual test. And if they're asking you to do a likelihood ratio test then I'm assuming that the class covered that.
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    Re: likelihood ratio test and AIC


    Quote Originally Posted by Dason View Post
    Google likelihood ratio test. Then note that there is more to it than just looking at the values and seeing which one is 'better'. Like I said the likelihood for the full model will always be "better" so just comparing directly doesn't really tell us anything. You need to do an actual test. And if they're asking you to do a likelihood ratio test then I'm assuming that the class covered that.
    LRT=-2(94.27-(-90.83))=6.88
    Chi Square (0.05) df=3 = 7.815
    since
    6.88<7.815 not significant
    so model 1 is better.

    is this correct?

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