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st: PCA


From   "[email protected]" <[email protected]>
To   [email protected]
Subject   st: PCA
Date   Fri, 16 Jan 2009 13:23:24 +0100 (CET)

hELLO!

I want to use a PCA with a dataset of  17 variables (congeners) 
measured in 120 food and air samples.
The concentrations are expressed in 
different units of measurement (ng/Nm3, ng/kg)
Is it correct assign to each 
variable a value that corrispond to the concentration measured for the 
congener, reported in relation to the sum of the 17 congener concentrations?

I 
use the covariance matrix in PCA, with this output:

    
--------------------------------------------------------------------------

       Component |   Eigenvalue   Difference         Proportion   Cumulative

    -------------+------------------------------------------------------------

           Comp1 |     .0474947     .0380502             0.6869       0.6869

           Comp2 |    .00944454    .00531611             0.1366       0.8234

           Comp3 |    .00412843   .000944856             0.0597       0.8831

           Comp4 |    .00318357    .00184526             0.0460       0.9292

           Comp5 |    .00133831   .000309329             0.0194       0.9485

           Comp6 |    .00102898   .000329951             0.0149       0.9634

           Comp7 |    .00069903   .000190709             0.0101       0.9735

           Comp8 |   .000508321    .00011746             0.0074       0.9809

           Comp9 |   .000390861  .0000988767             0.0057       0.9865

          Comp10 |   .000291985   .000103161             0.0042       0.9908

          Comp11 |   .000188823  .0000422023             0.0027       0.9935

          Comp12 |   .000146621  .0000242402             0.0021       0.9956

          Comp13 |   .000122381  .0000341471             0.0018       0.9974

          Comp14 |  .0000882337  .0000235538             0.0013       0.9986

          Comp15 |  .0000646799  .0000359076             0.0009       0.9996

          Comp16 |  .0000287723  .0000287712             0.0004       1.0000

          Comp17 |  1.03334e-09            .             0.0000       1.0000

    --------------------------------------------------------------------------


2 principal components accounted for a total of 82% of variance in the data set


Is it correct?

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