You'd hope every diagnosis made about your health was evidence based, but there are five common assumptions doctors make that are getting in the way of good treatment.
Doctors' intuition can save lives, but it's also undermining efforts to reduce over-treatment and misdiagnosis of Australian patients, according to a review of medical bias published in the Medical Journal of Australia.
"Doctors are humans, and like every other human, are vulnerable to being biased," said Professor Ian Scott, director of Internal Medicine and Clinical Epidemiology at Brisbane's Princess Alexandra Hospital, and one for the authors of the study.
"A lot of the time our intuition is correct. We don't get it wrong that often. But where we get it wrong, we often over-investigate and over-treat."
An epidemic of over-treatment - too many scans, tests, prescriptions and operations - is costing the nation at least $40 billion a year as well as exacting a human toll of anxiety, pain and medical complications.
Up to one third of many medical procedures are now being done unnecessarily, according to an international review of common medical procedures published in The Lancet medical journal in January this year.
The most common cognitive bias held by Australian doctors, according to the report in the MJA, is perhaps the most understandable. It's the commission bias, or the urge to do something.
Doctors have a "strong desire to avoid experiencing a sense of regret (or loss) at not administering an intervention that could have benefited at least a few recipients", the report said.
A list of questions for doctors to ask themselves includes this one: "I may suffer (medico-legally or in other ways) if I do not do this - so am I treating myself or the patient?"
But the fear of getting sued for failing to prescribe a treatment could be exaggerated, Professor Scott said.
Even when patients sue over a delayed diagnosis, doctors are not always found to be at fault, he said.
"There are legal precedents that counteract the belief that if doctors don't do something, they will have an adverse opinion given to them."
Four other common biases are outlined in the report:
Attribution bias leads to "undue confidence in [the] effectiveness" of treatments that have been seen to work for some patients sometimes, such as surgery for back pain or chemotherapy for certain cancers.
Impact bias occurs when patients and clinicians "overestimate the benefits of any intervention and underestimate the harms".
Availability bias is reinforced when a dramatic, "emotionally charged and vivid" case leads to either a good or bad outcome, and doctors are more likely to assume all related cases will have the same result.
Ambiguity bias comes into play when the doctor doesn't know the problem is, but admitting so "may threaten clinicians' sense of authority and credibility". This can lead to what's known as "the cascades of care", as doctors order more tests and treatments, even the ones for which there isn't good evidence.
"These cognitive biases are widespread across all disciplines," Professor Scott said.
"GPs work in circumstances where there is greater uncertainty, often with patients who have vague presentations, so they might have more of an ambiguity bias. Specialists may have a stronger desire towards a commission bias, there's greater pressure for them to intervene."
The best way to combat these biases is for doctors to talk with each other more often, Professor Scott said, to debate the effectiveness of treatments and challenge their own assumptions.
