RE: st: Checking to see if the association between two variables is linear or otherwise

[Amal Khanolkar <Amal.Khanolkar@ki.se>]

Hi Justina,

Education is measured in years and the kind of degree qualification obtained - I have 6 categories of education: high school; no diploma, high graduate, some college, bachelors degree, masters degree etc

I see that if I plot histograms for BMI separately for each educational group - the distribution of BMI gets narrower as educational level increases (as expected) - which made me wonder that assuming a linear relationship between education and BMI (and thus using linear regression) may not be the best choice.

Do you mean, that I don't have to worry about the relationship being not linear then...?

Thanks,

/Amal,
________________________________________
From: owner-statalist@hsphsun2.harvard.edu [owner-statalist@hsphsun2.harvard.edu] on behalf of Justina Fischer [JAVFischer@gmx.de]
Sent: 13 October 2012 00:55
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: Checking to see if the association between two variables is linear or otherwise

Hi

unless education is measured in years I would create a set of dummy variables in educational level (i.education).

The effect of low education on BMI will then be driven by the systematic relation with BMI that exists for the _majority_ of the low-edu-population.

Pls do not forget to control for income - low education might correlate with low income, and low income earners may not afford healthy food.

HTH

Justina


-------- Original-Nachricht --------
> Datum: Fri, 12 Oct 2012 21:56:35 +0000
> Von: Amal Khanolkar <Amal.Khanolkar@ki.se>
> An: "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
> Betreff: st: Checking to see if the association between two variables is linear or otherwise

> Hi,
>
>
> I'm trying to figure out if linear regression is the appropriate choice
> for my research question - I would like to analyze the association of BMI and
> education (BMI is continuous and education categorical). Ideally I would
> just run a linear regression with BMI as the outcome and education as the
> principle explanatory variable.
>
> However my hypothesis is that low educated people are both likely to have
> a low and a high BMI, i.e. the association between education and BMI is
> probably more 'u shaped' than linear.
>
> What is the best way to check if the association between a continuous and
> categorical variable is linear or otherwise...? Preferably, I would like to
> be able to plot such a shape using Stata.
>
> Thanks,
>
> /Amal.
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