Austin Nichol wrote in reply to my question:
>Sure:
>corr y x
The problem is that I have non-independent observations. Longitudinal (panel) data. Multiple measurements per patient over time. Pearson's correlation assumes independence, therefore -corr- is not appropiate.
Thank you,
Ricardo.
Ricardo Ovaldia, MS
Statistician
Oklahoma City, OK
Ricardo Ovaldia<[email protected]> :
Sure:
corr y x
but I guess you have something else in mind--perhaps you could
clarify. Maybe you want to allow mean and SD to change over time, and
standardize by time e.g.
webuse psidextract, clear
corr lwage ed
ren lwage y
ren ed x
egen my=mean(y), by(t)
egen sy=sd(y), by(t)
egen mx=mean(x), by(t)
egen sx=sd(x), by(t)
g zy=(y-my)/sy
g zx=(x-mx)/sx
reg zy zx, nocons
corr zy zx
On Mon, Jul 20, 2009 at 9:51 AM, Ricardo Ovaldia<[email protected]> wrote:
>
> Dear all,
>
> Is there a way to estimate a correlation coefficient of two continuous measurements each collected over time on a sample of patients? Not sure if I can do this with -xtreg- for example.
>
> Thank you,
> Ricardo
>
>
> Ricardo Ovaldia, MS
> Statistician
> Oklahoma City, OK
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