a two-stage
stratified sampling process is employed to obtain an independent,
nationally representative sample each year. The core sample from
the general population is boosted by sampling from population
groups of interest in some years i.e. persons from ethnic minorities
in 2004. Interviewers obtain household, socioeconomic and
personal details, information on health and illness, and health
service use from respondents. Respondents aged above the age of
16 years are then visited separately by a trained nurse. The nurse
visit involves anthropometric measurements, blood and urine
samples. Respondents are asked for information about prescribed
medications