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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