All of the previous scenarios involve single-item measures; often, contributing studies use multi-item scales. In discussing multi-item scales within the IDA framework, we distinguish between creating harmonized items, a term which we use to refer to creating comparable items across studies (by transforming the original items/response scales), and creating commensurate measures, a term which we use to refer to creating scales which have the same meaning and metric across studies (by using measurement models). The process of creating commensurate measures is thus more complex than simple harmonization.
