The techniques used to examine the psychometric properties of instruments that measure concepts where individual responses are aggregated to form an index describing a group level phenomenon are reviewed. This examination includes assessing the content validity of items to determine how well they measure group level concepts as well as analyzing reliability and validity at the aggregated rather than individual level. Additional techniques to test for within and between group variability are presented. The latter approaches are useful in determining the consistency and adequacy of individual responses at the group level.
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