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# Re: st: How to implement Discrete Principal Component Analysis by using POLYCHORICPCA

 From 汪哲仁 To statalist@hsphsun2.harvard.edu Subject Re: st: How to implement Discrete Principal Component Analysis by using POLYCHORICPCA Date Fri, 6 Jan 2012 01:35:28 +0400

```Dear Cam,

result like this.
=================================================================================
pca foreign rep78 mpg

Principal components/correlation                  Number of obs    =        69
Number of comp.  =         3
Trace            =         3
Rotation: (unrotated = principal)             Rho              =    1.0000

--------------------------------------------------------------------------
Component |   Eigenvalue   Difference         Proportion   Cumulative
-------------+------------------------------------------------------------
Comp1 |       1.9703      1.34377             0.6568       0.6568
Comp2 |      .626528      .223359             0.2088       0.8656
Comp3 |      .403169            .             0.1344       1.0000
--------------------------------------------------------------------------

Principal components (eigenvectors)

----------------------------------------------------------
Variable |    Comp1     Comp2     Comp3 | Unexplained
-------------+------------------------------+-------------
foreign |   0.6084   -0.2732   -0.7451 |           0
rep78 |   0.5910   -0.4706    0.6551 |           0
mpg |   0.5296 0.8390    0.1249 |           0
----------------------------------------------------------

===================================================================================
but polychoricpca only give us results without eigenvectores, like below.
polychoricpca foreign mpg rep78

k  |  Eigenvalues  |  Proportion explained  |  Cum. explained
----+---------------+------------------------+------------------
1 |    2.206757   |    0.735586            |   0.735586
2 |    0.615445   |    0.205148            |   0.940734
3 |    0.177798   |    0.059266            |   1.000000

My question is that, after running polychoricpca procedure, how can I
know the eigenvectors to construct an index.

with kind regards,

Charles Wang
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```