This was estimated by assuming that the 44 sampled
diagnostic centres were representative of the population of
551 centres in terms of the number of tests per centre, allowing
Tdt to be calculated as 14,000 ± 1100. This approach is considered
reasonable, as the 44 sampled centres were found to be
quite homogeneous in terms of the number of tests per centre
per day (25 ± 2). However, it is likely that 551 is a slight underestimate
of the number of centres.