Introduction to special section on response shift at the item level

Methodological developments for detecting response shift have enabled increasingly sophisticated analyses over the past decade. While most response shift research has focused on effects on patient-reported outcome (PRO) subscales, the emergence of item response theory applications to PRO research led to the following questions: Does response shift at the item level have particular importance or significance, and is it worthwhile to address such effects in addition to subscale-level analysis? The International Society of Quality of Life Research (ISOQOL) Response Shift Special Interest Group (SIG) undertook an international collaboration to address these questions, and the resulting special issue is presented in this issue of Quality of Life Research. …