1. C

    Help me understand the unidimensionality assumption in test theory (CTT and IRT)

    De Ayala (2009) writes: This always made sense to me until recently. In any statement found in a psychological questionnaire, there is semantic overlap between constructs. Heck, we even allow factors to be correlated in obliquely rotaded PCAs and EFAs. As soon as any two factors are...
  2. E

    Psychometric sample size requirements

    Good afternoon, What is the guidance for psychometric sample size requirements? For instance, say I developed a psychometric tool to assess resilience with scores ranging from 0 to 100. Let’s say, the Los Angeles County Unified School District has agreed to use my tool to assess resilience...
  3. D

    Discriminant Function Analysis reveals cut off score?

    Hi everyone, I have a research project where I am looking at the psychometric properties of a new questionnaire about body image. I have two samples: an eating disorder sample and an undergrad control sample. I wanted to see how well my questionnaire discriminates between clinical cases...
  4. M

    One variable influencing the other

    Hey everyone! I'm new to statistics and would really appreciate some help. I have this one project, that I need to finish, and the objective of it is to see if one variable has any influence on the other. More precisely, I need to know if anxiety can influence the performance on tests (test...
  5. P

    Two CFA vs second-order CFA

    Hi All, I'm working on my dissertation, and am evaluating the internal structure of a 34-item scale. The model in which the scale is based off of is hierarchical, and is structured/ordered as such: (1st) items, (2nd) item-groups, & (3rd) sub-scales. To evaluate this information I would use a...
  6. H

    SPSS- How to do AUC/ROC analyses? Help

    Dear all, Would be grateful for any help/pointers. I've spent the weekend trying to work out how to do area under the curve (ROC) analyses in spss 18. I've done it a couple of years ago but just can't recall how to input the data and where to find the requisite commands! I have the...
  7. E

    Item difficulty/percentile ranking and z-score

    Hi I am taking a course in psychometrics and am studying for my final exam, which is in two days. I was going over some old exam questions and found one that confuses me: "What is the z-score of an item, which 16% answered correctly" Instinctively, I want to say 1.0. I am then...
  8. N

    Restriction of range

    Is it possible to control for restriction of range in SPSS and if so, how?
  9. D

    Psychometrics with small datasets?

    Hi, I am developing a new measurement scale for cannabis withdrawal, but only have 50 people in my dataset (they filled the scale in every day for 3 weeks - 1 week was a baseline smoking as usual phase, the other two were abstinence from cannabis). I want to do a full psychometric...
  10. D

    Using Generalized Estimating Equations to test item validity on a scale

    Hi, I am creating a new measurement scale for withdrawal from cannabis, and have daily withdrawal data from 50 people for 1 week before abstinence (baseline smoking as usual) and then for 2 weeks of abstinence. There are 26 items on this new scale, and essentially what I want to is to rank...