C1a took place from 10 March 1997 to 1 June 1998 and has been
described in more detail previously.
6
Participants were invited for
follow-up between 22 February 2008 and 11 February 2010. All the
information gathered and the procedures followed were standardized in both cities and similar in both studies. The study protocols were approved by the Danish Ethics Committee (No 2-16-4-0001-97 and VN 96/208mch and N-VN-19960208MCH, the
Northern Jutland Region Committee). All participants gave written
informed consent.