The men were recruited from seven European countries (centers). Each
centre began recruitment at a different time, ranging from 1991 to 1998.
The last entry was in December 2003. The uniform censoring date was
December 31, 2006. The randomization ratio was 1:1 in six of the seven
centres. In the seventh, Finland, the size of the screening group was fixed
at 32,000 subjects. Because the whole birth cohort underwent randomization,
this led to a ratio, for the screening group to the control group, of
approximately 1 to 1.5, and to the non-screening arm being larger than the
screening arm.
The randomization of the Finnish cohorts were carried out on January 1 of
each of the 4 years 1996 to 1999. This, coupled with the uniform December
31 2006 censoring date, lead to large numbers of men with exactly 11, 10, 9
or 8 years of follow-up.
Tracked backwards in time (i.e. from right to left), the Population-Time
plot shows the recruitment pattern from its beginning in 1991, and in
particular the Jan 1 entries in successive years.
Tracked forwards in time (i.e. from left to right), the plot for the first
3 years shows attrition due entirely to death (mainly from other causes).
Since the Swedish and Belgian centres were the last to close their
recruitment - in December 2003 - the minimum potential follow-up is three
years. Tracked further forwards in time (i.e. after year 3) the attrition
is a combination of deaths and staggered entries.