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Validating test items with spss

The responses to the questionnaire are on a Likert scale; can anyone suggest any further tests to apply to help test its validity.

I am not an expert on statistics so any help would be appreciated.

I'll assume that you have, at this point, calculated the descriptive statistics et al. Use a form of factor analysis (not principal components) and an oblique rotation for each number of factors.

If not, the psych package has a describe() function which should give you the stats you need. If your factors do not appear to be correlated after an oblique rotation, switch to orhogonal rotation.

There are additional assumptions like, e.g., local independence (i.e., the correlations between responses are explained by variation on the ability scale).

Anyway, you will find a very complete documentation and useful clues to apply psychometric methods in R in volume 20 of the Journal of Statistical Software: Special Volume: Psychometrics in R.

by trying to induce such patterns with experimental manipulations, or using a think-aloud procedure ["protocol analysis", Ericsson & Simon, 1992]). patients with controls) that should have differing scores.

Or correlate it with an external criterion that should be correlated with the trait you're measuring.

This is as an orthogonal structure can be determined from an oblique rotation, but not vice versa.

Extract all the factor solutions between the MAP criterion and the parallel analysis criterion.

I am designing a questionnaire for my dissertation.

I am in the process of validating the questionnaire I have applied a Cronbach's alpha test to the initial sample group.

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