Because of this variance-bias trade-off, the results of a randomized screening trial vary with the length of follow-up after the last screening.
The CNBSS consists of two randomized screening trials of 98 835 women aged 40 59 recruited at 15 Canadian centres between 1980 and 1985.
Large randomized screening trials provide an estimation of the effect of screening at a population-based level.
In theory, overdiagnosis can be estimated by comparison of incidence in a randomized trial of screening, but this would require that the control group was never screened and that both intervention and control groups were followed up to expiry or for more than at least two decades.
Thus, in the CNBSS, as in other individual randomized screening trials, a substantial underestimation of the screening effect through contamination cannot be ruled out.
The National Breast Screening Study (NBSS) was a randomized trial of screening with mammography and physical examination [ 13].
Suppose we wish to design a randomized trial of screening in this population.
Prediction of deaths and surrogate end points can be used to estimate the required sample size and duration for designing a randomized trial of screening for NPC.
The beliefs of professionals are supported by the findings of a randomized trial of screening for suicidal thoughts which found no ill effect and some evidence of benefit [ 30].
The New Technologies in Cervical Cancer (NTCC) study is a randomized trial of screening methods (conventional cytology versus HPV testing) for which the main endpoint was histologic detection of cervical intraepithelial neoplasia of grade 2 or more.
