25 years ago the International Society of Quality of Life Research was founded with a mission to advance the science of quality of life and related patient-centered outcomes in health research, care and policy. While focusing on quality of life (QOL) in healthcare may seem like a no-brainer, measuring it is not as easy as conducting a blood test to detect disease. Medical professionals have used surveys and questionnaires for many years, and they are vital elements in health care assessment and diagnosis. Insurance companies use them to determine degree of disability in qualifying patients for long-term care benefits, for example. An internet search reveals 34 different survey instruments used in diagnosing and assessing strokes and post-stroke rehab.

Survey instruments such as these are inherently subjective and subject to self-report and other bias. Still, despite their qualitative foundation their outcomes must usually be converted into decisions. The founding of ISOQOL formalized and accelerated the application of statistical methods to the study of QOL instruments, helping to answer questions like How reliable is a survey instrument? Does an instrument measure what we think it does? How do instruments A and B (and C, D, etc.) compare and relate to one another?