What is Item Response Theory

This chapter provides an introduction to a variety of essential issues concerning quality of life (QoL) as a social-scientific construct. The chapter begins with an introduction to the notion of QoL as an essentially contested concept and provides a taxonomy for classifying various instruments. The various methods of operationalizing the measurement of health-related quality of life (HRQoL) are outlined and a variety of practical examples are provided. A range of methods of determining the validity, reliability, and responsiveness of QoL measures are discussed to provide the reader with the tools necessary to critically evaluate the broad range of QoL instruments available. Finally, the scope of employment of QoL instruments is explored and several important limitations of this mode of assessment are discussed.