Analyzing mammograms is a repetitive task, so researchers took a closer look at accuracy rates to see if medical staff are less likely to spot breast cancer at the end of reading a batch of 35 mammograms.
The results, published in the Journal of the American Medical Association, of their analysis surprised them.
“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,” says Sian Taylor-Phillips, a researcher at the University of Warwick who led the study.
“They recalled fewer women for further tests as they got nearer the end of the batch while cancer detection rates stayed constant.”
“Psychologists have been investigating a phenomenon of a drop in performance with time on a task called ‘the vigilance decrement’ since World War II. In those days radar operators searched for enemy aircraft and submarines which appeared as little dots of light on a radar screen,” says Taylor-Phillips.
“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.”
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 scrutinize batches of around 35 women’s mammograms.
Breast x-rays or mammograms show lots of overlapping tissue and cancers can be quite difficult to spot.
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, randomized 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.
While 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.
Taylor-Phillips and her team are going to expand their research in this area. They are currently analyzing how performance changes over longer reading sessions, and whether examining mammograms at different times of day affects performance.
Source: University of Warwick