Problems and issues with door-to-door, two-phase surveys: an illustration from central Spain

In 1994-1995, a screening and examination survey was conducted to ascertain the prevalence of dementia, Parkinson's disease and stroke in two urban communities and one rural community of central Spain. We use this survey to illustrate many nonclinical aspects of conducting two-phase prevalence surveys. Special emphasis is given to two common weaknesses in such surveys: screening nonparticipation and screening validation.