After 1900 individuals had been invited using the recruitment process detailed above, a second invitation was sent out to give the non-responders another chance to participate and to increase the response rate. Due to the confidentiality of the CHI, it was not possible to contact only those who had not responded to the first invitation. Rather, all individuals invited up to that time were re-mailed. In total, second invitations were sent to 1741 individuals (this is lower than the 1900 previously invited due to updating of the CHI over time). From this second invitation, 615 responses were received (35.3% of those mailed). Seventy eight were not marked as interested or not interested although, of these, 4 were returns from incorrect addresses, 52 noted that they had already participated, and 22 marked that they were ineligible. Of the 321 who responded as not interested, 44 were ineligible, and 5 had already attended; the remaining 272 gave no reason. Two hundred and sixteen individuals were interested, but this included 62 who were already participants in the study, and 45 who were ineligible.
