Data were collected by computer-assisted telephone interview initially in 2003 (T1), at the 2-year follow-up in 2005 (T2), and at the 5-year follow-up in 2008 (T3). Before calling the participants, a letter explaining the study aims and the procedures was sent out. At T2 and T3 letters were sent to participants who had agreed to take part in the follow-up. If necessary, an extensive search was undertaken to find their new addresses and phone numbers, including checking different telephone directories and contacting the Residents’ Administration Offices. If the new telephone number could not be found, or after 40 unsuccessful attempts to reach participants, they were allocated to the dropout group. At the 5-year follow-up, the option of completing an online questionnaire instead of a telephone interview was offered to those who lived abroad.
