I am investigating a scale of consumer ethnocentrism - CETSCALE. I do not have much knowledge in econometrics, scales, etc., however:
a) research papers report that the standard 17-item scale is reliable and valid (some papers support also unidimensionality, but some multidimensionality)
b) some research papers use the same questions, but reduce the number from 17 to 10 items and also report scale reliability and validity
c) there are some that even use only 7 items from the same scale
The questions are -
a) what does it mean that both scales are reliable and valid?
b) how it can be that both of them are reliable / valid if both have similar questions (questions are similar, but 10-item scale is reduced)?
I want to use such a scale in my research, but I do not get which one to use.
I prefer smaller number of items in my questionnaire, but I am confused -
c) which one should I use if both are valid and reliable (based on research papers) -- are there some criteria that can help to determine which would be better to use?