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    Logistic regression - basics




    Dearest stat colleagues,

    I have some basic questions regarding logistic regression that I hope you can help me out with.

    Iím running a simple logistic regression - output is attached. I need to calculate how much odds of smoking (smoker) is expected to fall/increase by when age increases by 10 years. Iíve read that it can be calculated in the following way:

    0,99326^10 = 0,9346

    Could you briefly explain if this is the correct method? Or should I multiply it with the constant - if yes why?

    Iím also asked to calculate the odds of smoking of a 70-year old person when all x-variables are 0. Is it like this and why?
    0,467*0,99326^70 = 0,29?

    Your help is greatly appreciated. Thanks.
    Jeff
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    Re: Logistic regression - basics

    In principle your computations were correct, but rounding errors can quickly become very big. The easiest and safest solution is to create a new variable gen age10 = (age -70)/10, and add age10 instead of age. Now your constant will be the odds of smoking for a 70 year old person with all other xs set at 0, and the odds ratio for age10 will be the ratio change for a 10 year increase in age.

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    Jeff135 (06-01-2016)

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    Re: Logistic regression - basics

    I am not too familiar with STATA, but also you have all of your categorical variables entered as categorical variables into the model, yes?
    Stop cowardice, ban guns!

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    Re: Logistic regression - basics

    Thanks for the reply maarenbuis. It produces the correct result - could you please explain me briefly why? What does age10 tell?

    Thanks

    Jeff

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    Re: Logistic regression - basics


    Quote Originally Posted by hlsmith View Post
    I am not too familiar with STATA, but also you have all of your categorical variables entered as categorical variables into the model, yes?
    Yes, all variables except for age are categorical variables/dummies.

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