Reaching and engaging hard-to-reach populations with a high proportion of nonassociative members.

Unlike research on "associative" hard-to-reach populations, such as those at risk of AIDS, which has been subject to extensive methodological scrutiny, few studies have explored strategies for researching nonassociative hard-to-reach populations: those whose members do not normally have contact with other members. This article contributes toward rectifying this imbalance. The literature review includes issues of representativeness, use of membership lists or other centralized sources of information, innovative ways of gaining access to nonassociative population members, and an overview of multiple approaches. The authors then explore strategies adopted by one of them in recent studies of three such populations in the United Kingdom of people with spina bifida and hydrocephalus, advanced Parkinson's disease, and skeletal dysplasia resulting in very short stature. They consider previously unreported problems with using membership lists and discuss strategies for finding population members not in contact with others in the population or membership organizations or professionals.