Re: convergent validity

[Paul R Swank]

You could do this best with a confirmatory factor analysis which would allow you to "compare" coefficients by restricting them to be equal. The measurement problem would be an issue for some programs although MPlus allows factor analysis with ordered categorical responses. It would require you having a sufficient sample size, but that would depend on the number of parameters in the model which is a function of the number of items and the number of expected latent variables. The typical minimum number is 200 although I have seen some papers with fewer than that.

At 08:30 PM 3/29/01 +0200, you wrote:
>Hi Statisticians,
>
>First of all, sorry for posting my question in 3 groups, but I'm a bit
>of a newby here and I can't find out what the difference is (where can I
>read the Charters, or whatever it's called?).
>
>I would love to have some help on the following:
>
>I have 2 questionnaires assessing (physical and emotional) health of
>heart patients. The 1st measures present state and it's assessed before
>treatment and a couple of months after treatment, so that difference
>scores can be calculated. The 2nd questionnaire is assessed after
>treatment only, and asks respondents how much they have changed on every
>aspect (same aspects as the first questionnaire) since just before
>treatment.
>Respondents received both questionnaires. Now I would like to
>investigate the convergent validity of the two domains assessed with
>both questionnaire versions. Is there a standard, straightforward way of
>doing this? Someone advised me to do a factoranalysis (PCA) (on the
>baseline items, the serially measured change scores and the
>retrosepctively assessed change scores) and then compare the
>factorloadings (I assume after rotation? (Varimax?)). I haven't got a
>good feeling about this method for two reasons:
>- my questionnaire items are measured on 5- and 7-point Likert scales,
>so they're not measured on an interval level and consequently not
>(bivariate) normally distributed;
>- I have no idea how to compare the factorloadings. Could I calculate
>confidence intervals for the loadings? (If yes: how?)
>
>Thanks in advance for any help or references.
>
>Heike
>
>
>
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------------------------------------
Paul R. Swank, PhD.
Professor & Advanced Quantitative Methodologist
UT-Houston School of Nursing
Center for Nursing Research
Phone (713)500-2031
Fax (713) 500-2033

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