Approximately 10-14% of adults The group of people being studied. Populations may be defined by any characteristics e.g. where they live, age group, certain diseases. have moderately to severely disabling A health condition marked by long duration, by frequent recurrence over a long time, and often by slowly progressing seriousness. For example, rheumatoid arthritis. pain: we need to know what works and what doesn’t work to help them manage their pain.