chronic difficulties was completed by each respondent. In
1989/90, (Phase 2), repeat questionnaire data were collected
by post, and between 1992–1993 a further round of clinical
screening and questionnaire data collection was completed
(Phase 3). Phase 4, a postal questionnaire, was completed in
1995/6 and further screening and questionnaire data were
collected between April 1997 and August 1999, Phase 5. Data
for this work were derived from Phase1, Phase 4, and Phase 5.