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Assessment of changes to screening programmes: why randomisation is important

BMJ 2015; 350 doi: (Published 30 March 2015) Cite this as: BMJ 2015;350:h1566
  1. Katy J L Bell, NHMRC early career research fellow1,
  2. Patrick Bossuyt, professor of clinical epidemiology2,
  3. Paul Glasziou, director1,
  4. Les Irwig, professor of epidemiology3
  1. 1Centre for Research in Evidence Based Practice, Bond University, QLD 4229, Australia
  2. 2AMC, Amsterdam, Netherlands
  3. 3Screening and Test Evaluation Program, School of Public Health, University of Sydney, Australia
  1. Correspondence to: K J L Bell katy.bell{at}
  • Accepted 17 February 2015

Screening programmes sometimes need to be adapted as new technologies and treatments become available. Katy Bell and colleagues argue the best way to assess such changes is through randomised trials within the programmes

Randomised controlled trials provide the best evidence of the benefits and harms of screening. Yet, once a screening programme is started, uncertainty may remain about specific components of the strategy. For example, what test should we use to screen for colorectal cancer? How long should we wait before re-screening? Should potential participants be given an information booklet? The screening technology itself is continually evolving and often there is uncertainty about to whether to introduce new testing methods, such as liquid based cytology for cervical cancer1 or 3D mammography to screen for breast cancer.2

We believe that such decisions should be based on the strongest available evidence. This requires pragmatic trials within the screening programme, with the eligible population randomised to different screening strategies. Here, we use the example of bowel cancer screening to show why randomisation is needed and how it can work. However, the general principles can be applied to population screening for other conditions.

Why randomise?

Although randomised controlled trials show that offering faecal occult blood testing prevents death from colorectal cancer, there is little evidence about which test should be used. Most trials used guaiac faecal occult blood tests, but since then several immunochemical tests have become available and are claimed to have better performance. There have also been suggestions that the threshold for diagnosis should be modified according to previous risk and that the screening interval be based on cancer risk .3 Randomisation within screening programmes can inform these decisions and help prevent problems, as the experience of the Australian screening programme shows.

Australia’s screening programme for bowel cancer started in August …

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