Background

In the health and medical fields, most quality of life (QoL) measures focus on health-related quality of life (HRQOL) or the functional effects of respondents ’ perceived mental and physical health [1]. However, as Gill and Feinstein [1] note, QoL is a reflection of respondents’ perceptions and reactions to not only their mental and physical health, but also to non-health related aspects of their lives (e.g., family, friends, work). A recently developed QoL measure, the Injection Drug User Quality of Life (IDUQOL) scale, was designed to capture the health and non-health related aspects of injection drug users ’ (IDUs) lives that comprise important components of their QoL, particularly given their individual circumstances and environment [2, 3]. IDUs live in a distinct environment characterized by a high prevalence of infectious disease, crime, violence, and lack of stable housing. Many IDUs cannot depend on basic necessities and experience considerable instability in many aspects of their lives. When selecting and using an instrument, it is important that there be validity evidence that the instrument is meaningful, useful, and appropriate for a given population in a given context [4-6]. Previous research on the IDUQOL has examined content validity via subject matter experts (SMEs) [7] as well as factor structure, internal consistency, test-retest reliabilit