# Re: st: RE: PCA, reverse scorings

 From Juan Julio Gutierrez <[email protected]> To [email protected] Subject Re: st: RE: PCA, reverse scorings Date Sun, 30 Dec 2007 11:33:53 -0800 (PST)

```Thanks Maarten and Jay,

I have tried to follow Jay's suggestion "to pick reference items to fix the signs of the solution"
without luck.

If you could provide guidance on this, it would be greatly appreciated.

Thank you

Juan Julio

--- "Verkuilen, Jay" <[email protected]> wrote:

> >>I am working on creating an index using PCA.
> When running PCA the first time, with the original values the loadings
> come up with some unexpected signs<<
>
> reflection. You have to pick reference items to fix the signs of the
> solution. As Maarten noted, you're getting exactly the same scores back.
>
>
> Jay
>
> *
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,
>
>  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:
>
>
>  newskillw	0.51811
>  eduatt	         0.576
>  rd	         0.55153
>  newitexp	0.30919
>
> Now I get loadings that make sense. However when using the score
> 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

-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands

Buitenveldertselaan 3 (Metropolitan), room Z434

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