Breast cancer detection rates of mammogram readers don't decline over time

• Breast cancer detection rates of mammogram readers don't decline over time
• Accuracy of staff who report results doesn't drop towards end of a batch of readings
• Study suggests fewer recalls are made towards the end of batch

A new study has found there is no decline over time in the accuracy of medical staff who analyse mammogram scans for indications of breast cancer.

Research conducted at the University of Warwick investigated whether detection rates dropped towards the end of each batch of mammogram readings.

The study Improving breast cancer screening detection rates through understanding, modelling, and adapting patterns of radiologist performance has been published in JAMA, the Journal of the American Medical Association. The research was conducted by Dr Sian Taylor-Phillips who was funded by an NIHR Doctoral Research Fellowship.

Dr Taylor-Phillips examined whether a phenomenon called 'the vigilance decrement' would apply in which accuracy of repetitive tasks decreases over time.

Breast x-rays or mammograms show lots of overlapping tissue and cancers can be quite difficult to spot. To the research team's surprise they found that the cancer detection rates throughout each batch of approximately 35 readings didn't change. They had expected accuracy to decline towards the end of each batch.

Dr Taylor-Phillips said: "We found no reduction in performance or vigilance decrement at all. In fact, we found the opposite of what we were expecting - breast screening readers seemed to get 'into the zone' and their performance improved with time on task. They recalled fewer women for further tests as they got nearer the end of the batch while cancer detection rates stayed constant."

In the UK National Health Service Breast Screening Programme two readers separately examine each woman's mammograms for signs of cancer. Women have mammograms taken of both breasts and these are examined for signs of cancer by trained staff. Both readers scrutinise batches of around 35 women's mammograms. Current practice is that both readers examine the x-rays in the same order as one another, so if they both experience a vigilance decrement, the vigilance will be low for both readers when examining the same women's mammograms.

To test the vigilance decrement theory the researchers changed the case order for the two readers expecting them to experience low vigilance when examining different women's mammograms. A real-world randomised controlled study in UK clinical practice was conducted incorporating 1.2 million women's x-rays in the trial.

As well as finding no effect on cancer detection rate, in an exploratory post-hoc analysis, they found that their overall performance improved with time on task.

Whilst the readers kept up a constant rate of detecting cancer, the number of women they recalled for further tests to achieve this decreased over time. When readers first sat down and started the task they recalled on average 6.4 women per thousand screened, this decreased to 4.6 per thousand screened after examining 40 women's mammograms in a row.

Dr Taylor-Phillips said: "Psychologists have been investigating a phenomenon of a drop in performance with time on a task called 'the vigilance decrement' since World War 2. In those days radar operators searched for enemy aircraft and submarines which appeared as little dots of light on a radar screen.

"People thought that the ability to spot the dots might go down after too much time spent on the task. Many psychology experiments have found a vigilance decrement, but most of this research has not been in a real world setting, unlike our study."

Dr Taylor-Phillips and her team are going to expand their research in this area. They are currently analysing how performance changes over longer reading sessions, and whether examining mammograms at different times of day affects performance.

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For media enquiries please contact Nicola Jones, Communications Manager, University of Warwick 07920531221 or N.Jones.1@warwick.ac.uk

List of authors:
Sian Taylor-Phillips, Warwick Medical School, the University of Warwick
Matthew G Wallis, Cambridge Breast Unit, Cambridge Universities NHS Foundation Trust and NIHR Cambridge Biomedical Research Centre,
David Jenkinson, Warwick Medical School, the University of Warwick
Victor Adekanmbi, Warwick Medical School, the University of Warwick
Helen Parsons, Warwick Medical School, the University of Warwick
Janet Dunn, Warwick Medical School, the University of Warwick
Nigel Stallard, Warwick Medical School, the University of Warwick
Ala Szczepura, Warwick Medical School, the University of Warwick
Simon Gates, Warwick Medical School, the University of Warwick
Olive Kearins, Screening QA Service (Midland & East)
Alison Duncan, Warwickshire, Solihull and Coventry Breast Screening Service, University Hospitals Coventry and Warwickshire,
Sue Hudson, Peel & Schriek Consulting Limited
Aileen Clarke, Warwick Medical School, the University of Warwick

The National Institute for Health Research (NIHR) is funded by the Department of Health to improve the health and wealth of the nation through research. The NIHR is the research arm of the NHS. Since its establishment in April 2006, the NIHR has transformed research in the NHS. It has increased the volume of applied health research for the benefit of patients and the public, driven faster translation of basic science discoveries into tangible benefits for patients and the economy, and developed and supported the people who conduct and contribute to applied health research. The NIHR plays a key role in the Government's strategy for economic growth, attracting investment by the life-sciences industries through its world class infrastructure for health research. Together, the NIHR people, programmes, centres of excellence and systems represent the most integrated health research system in the world. For further information, visit the NIHR website (http://www.nihr.ac.uk).

The research is also supported by the NIHR CLAHRC West Midlands initiative