Objective-The aim was to assess the extent to which selection bias affects a casecontrol study of breast cancer screening in which attenders and non-attenders for screening are compared.Design-There were two retrospective case-control studies, one estimating the risk ofdeath from breast cancer in women in the screening district relative to those in the comparison district (study A), the second estimating the relative risk for women who had ever been screened compared with women who had never been screened in the screening district alone (study B The evidence to date for the effectiveness of screening in reducing mortality from breast cancer has come from randomised trials,'4 from population based studies for which control populations were available,5 and from case-control studies conducted for population based screening programmes with no control population.6-8The United Kingdom trial of early detection of breast cancer (TEDBC), while not a randomised trial, included four separate "comparison" populations, from which the same data on breast cancer incidence and mortality were collected as in the four "intervention" districts.9 The first results on mortality from this trial showed a reduction in breast cancer mortality in the two districts offering annual screening of 140% relative to the comparison districts; this reduction increased to 20% when the breast cancer mortality in the different districts in the 10 year period before the start of the trial was taken into account.5The present study is a case-control evaluation comparing one of the screening districts with one of the comparison districts in this trial. A second case-control evaluation was conducted solely within the screening district, and compared screened and unscreened women. The purpose of undertaking two studies was to assess the extent of selection bias in the latter comparison. A subsidiary aim was to collect additional information on risk factors in order to estimate any underlying difference between the two districts and the extent to which such differences might have affected the results of the trial. MethodsThe methodology of the trial has been described in detail elsewhere. The present study includes data from Guildford, where screening was offered to all women aged 45-64 years by mammography and clinical examination every two years, with clinical examination in the intervening years; and Stoke-on-Trent, which acted as one of the comparison districts. In both districts the entire trial population has been flagged at the National Health Service Central Registry, which supplies the TEDBC coordinating centre with information on all breast cancer registrations and deaths. In Guildford, 72% of women accepted the initial invitation to screening and information on a number of risk factors for breast cancer was
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.