Message-ID: <3EDA4D9B.4050609@pdf.com>
Date: 2003-06-01T19:01:47Z
From: Spencer Graves
Subject: compositional data: percent values sum up to 1
What are you trying to do? What I would do with this depends on many
factors.
spencer graves
Christoph Lehmann wrote:
> again, under another subject:
> sorry, maybe an all too trivial question. But we have power data from J
> frequency spectra and to have the same range for the data of all our
> subjects, we just transformed them into % values, pseudo-code:
>
> power[i,j]=power[i,j]/sum(power[i,1:J])
>
> of course, now we have a perfect linear relationship in our x design-matrix,
> since all power-values for each subject sum up to 1.
>
> How shall we solve this problem: just eliminate one column of x, or
> introduce a restriction which says exactly that our power data sum up to
> 1 for each subject?
>
> Thanks a lot
>
> Christoph