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Re: st: PCA, reverse scorings
The two factors should be exactly the same. The original factor is
created using the folowing formula:
F1 = -0.51811*skillw + 0.5766*eduatt + 0.55153*rd + -0.30919*itexp
The new factor is created using the following formula:
F2 = 0.51811*-1*skillw + 0.5766*eduatt + 0.55153*rd + 0.30919*-1*itexp
The two formulae are exactly the same.
-- Maarten
--- Juan Julio Gutierrez <[email protected]> wrote:
> I am working on creating an index using PCA.
> When running PCA the first time, with the original variable values,
> the loadings come up with some unexpected signs
>
> KI index loadings
> original variables
>
> skillw -0.51811
> eduatt 0.576
> rd 0.55153
> itexp -0.30919
>
> I would expect that skillw and itexp would have positive values
> affecting the new variable I
> create with the command score (I am susing STATA 8).
>
> Reverse scoring: I have multiplied both variables (skillw and itexp)
> by -1 to get the opposite
> sign. the results now are:
>
> KI index loadings
>
> newskillw 0.51811
> eduatt 0.576
> rd 0.55153
> newitexp 0.30919
>
> Now I get loadings that make sense. However when using the score
> command to save the loadings and
> listing the values, both new variables (i.e. w. original variables
> and with opposite sign) are
> exactly the same.
>
> I would assume that the values should be different providing the
> different signs of the loadings.
-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands
visiting address:
Buitenveldertselaan 3 (Metropolitan), room Z434
+31 20 5986715
http://home.fsw.vu.nl/m.buis/
-----------------------------------------
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