Hi everyone! I am trying to find the "how to" on item difficulty and discrimination on SPSS and its interpretation. I have read about and performed the command analyze> scale> reliability analysis, to get the corrected item total correlations (which I believe can be interpreted as a dicrimination analysis...?). I also watched videos that teach that you could calculate dificulty index by calculating means and sums in the analyze> descriptive statistics> frecuencies and interpreting the means. But this is a different method to the one I read about in books and articles (rbis).
I am using this article as reference:
Article Best Practices for Developing and Validating Scales for Heal...
It describes item correlation, discrimination index and difficulty index as different methods for item reduction. Is it adecuate to use just one or two of these analysis? Must we use all at the same scale construction proyect? According to the item correlation method, I only keep 4 of 30 initial items from the scale so far.
Proyect Description: Scale construction with 30 initial dichotomous items (True/False)
Maria Acevedo Velazquez, just quickly in case it helps, I think that obtaining item-total correlations (through the reliability section of SPSS) is not going to give you the kind of answers that you want.
I think you also need to be clear about what is mean by discrimination. In some contexts, it means that scores on one construct are different from scores on another construct so that researchers are assured they're not just measuring the same construct in two different ways. In your context (from what I can pick up from your question), you want to be able to discriminate participants one from the other. That's a different kettle of fish.
I hope my pointing out those different things (both of which are dealt with in the Boateng et al. article that you mention) helps you set your sights a bit more clearly.
CTTITEM: SAS macro and SPSS syntax for classical item analysis
https://www.youtube.com/watch?v=XxlhV0Zm9-4
Robert Trevethan Thanks for your help! I also feel uneasy about interpreting the item-total correlations (been looking at the corrected column on the output). My intention is to perform item reduction analyses for scale construction on SPSS. Been able to determine which items are too easy or difficult, and which items fit better together to measure a construct.
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