ABSTRACT
This chapter discusses the concepts and measurement ideas underlying measures of disease impact. It presents examples of disease impact measures: the Headache Impact Test (HIT-6), the Asthma Control Test, and the Pain Impact Questionnaire. The chapter describes the development, the psychometric properties, and the interpretation of scores. Disease impact tests typically include items measuring symptoms as well as items measuring disease impact. The psychometric properties of the disease impact measures are specific to each measure and the populations where it is used. Item response theory information functions and content validity were considered in selecting a subset of items for a short version of the HIT question pool. The final phase in the development of the HIT-6 consisted of a linguistic translation of the six items into 27 languages. The chapter also discusses the issues of disease impact assessment in case of multimorbidity and the practical applications in population health and primary care.
