The 1930's HCS follows over 3,000 men and women who were born between 1931 and 1939, and still resident in the English county of Hertfordshire. The participants were recruited from birth records and completed their baseline assessments in 1998-2004, when they were 59-73 years old. The NHS Central Register at Southport in the United Kingdom was used to trace potential HCS participants whose birth and infant data were recorded in historical Hertfordshire birth records.