The initial contact with possible participants was made via Lothian Health Board, in a letter signed by the Director of Public Health. Researchers are not allowed to write to people on the CHI database directly. The mailing consisted of a letter from Lothian Health Board, an information sheet explaining why the contact was made by Lothian Health Board, an invitation letter written and signed by Professor Ian Deary (LBC1936 Study Director), an explanatory leaflet for the LBC1936 study, and a reply slip and a pre-paid reply envelope. The reply slip asked for normal contact details and date of birth, country of schooling, and schools attended. Individuals were also asked to indicate whether they were or were not interested in hearing more about the LBC1936 study. The reply slip was returned to the LBC1936 research team at the University of Edinburgh. This allowed the first direct contact between potential participants and researchers. Individuals were invited about 200–300 at a time (roughly according to postcode districts) to allow the LBC1936 study team to manage the responses efficiently.
