http://www3.who.int/whosis/discussion_papers/pdf/paper35.pdf

To understand the challenge of cross-population comparability, this paper reviews the basic paradigm for measurement of health status in multiple dimensions. The problem with the comparability of results is formulated in terms of response category cut-point shift, sometimes called differential item functioning in the psychometric literature. The main part of the paper presents a series of alternative methods to address the problem of response category cut-point shift in order to enhance cross-population comparability of results.