Item grouping effects on invariance of attitude items

The purpose of this study was to evaluate the effects of item grouping on local independence and item invariance, the characteristics of items scaled under the Rasch model that make them sample-free. Item fit and calibration for attitude items presented in a grouped versus random order were examined. It was hypothesized that grouping items to facilitate interpretation central to a construct may result in a failure of invariance. Data were 107 responses to a 40-item mail survey of teachers' opinions about the Ontario Ministry's grade 9 literacy test. Effects of grouping and item phrasing on invariance were found. Results, however, generally support the use of grouping of items to provide a higher person separation, and potentially higher quality data.