As a heart attack survivor who was sent home from the E.R. with a misdiagnosis of indigestion despite presenting with textbook symptoms (central chest pain, nausea, sweating and pain radiating down my left arm), I’m pretty interested in the subject of why women are far more likely to be misdiagnosed in mid-heart attack compared to our male counterparts.
Dr. Pat Croskerry is pretty interested in the subject of misdiagnosis, too. He’s an Emergency Medicine physician, a patient safety expert and director of the critical thinking program at Dalhousie University Medical School in Halifax. In fact, he implemented at Dal the first undergraduate course in Canada about medical error in clinical decision-making, specifically around why and how physicians make diagnostic errors. Every year, he gives a deceptively simple critical thinking quiz to his incoming first-year med students.
So here’s your chance to practice thinking like a doctor. Try answering these yourself, but as Dr. Croskerry advises, don’t think too hard. If you were an Emergency Department physician, paramedic or first responder, he warns, you’d have only seconds to size things up and make a decision. Don’t read ahead to peek at the answers! Now, here are your questions:
1. A bat and a ball cost a total of $1.10. The bat costs $1 more than the ball. How much does the ball cost?
2. If five machines take five minutes to make five widgets, how long would it take 100 machines to make 100 widgets?
3. In a lake with a patch of lily pads in the centre, every day the patch doubles in size. If it takes 48 days for the patch to cover the entire lake, how long did it take for the patch to cover half the lake?
4. A study of 1,000 people includes five engineers and 995 lawyers. A randomly selected participant named Jack is 36 years old, unmarried, introverted, likes to write computer programs, and reads science fiction in his spare time. Is Jack most likely to be an engineer or a lawyer?
Here are the answers:
1. The bat costs $1.05 and the ball costs five cents. (Most people would say that the bat costs $1 and the ball costs ten cents, which would make the bat $.90 more than the ball, not $1).
2. It takes 100 machines five minutes to make five widgets (as it would take 1,000 machines five minutes as well; the time would remain the same, not 1,000 minutes as most people might say).
3. If the patch of lilies doubles every 24 hours, then the day before the 48th day, the patch would be half what it is on the following day (not 24 days as many would guess).
4. Jack is a lawyer – who’s already been described as a “randomly selected” participant, meaning that the chance of him being one of the five engineers is only .5%. *
How did you do? Only 2-3% of Dr. Croskerry’s brainy med students get all four quiz questions right. As he told the Halifax Chronicle Herald last year:
“During the last 40 years, work by cognitive psychologists and others has pointed to the human mind’s vulnerability to cognitive biases, logical fallacies, false assumptions and other reasoning failures.
“It seems that much of our everyday thinking is flawed – and clinicians are not immune to the problem.”
He tells his medical students that about 75% of diagnostic errors are not due to a knowledge deficit, but to cognitive failures, or the way that people think.
Cognitive failures may be linked to the lack of what’s called situational awareness. This involves:
- knowing what has gone before
- what is happening now
- anticipating what is coming
- having one’s cognitive engine in the right gear
For many years, researchers have studied how critical signals guide decision-making (for example, Swets et al. 1961). But Dr. Croskerry warns that few signals arrive in complete isolation. They’re usually accompanied by some degree of noise or interference, as he explains:
“Similarly in medicine, a particular problem for physicians is the degree of overlap among diseases. Some conditions (like shingles, basal skull fracture or shoulder dislocation, for example) usually present little challenge for diagnosis; they are relatively unambiguous and readily identified, and accompanied by very little noise.
“Other diseases (pericarditis and acute myocardial infarction, for example) manifest themselves less clearly and may be mimicked by other conditions.
“Worse still, some conditions (such as ureteral colic and dissecting abdominal aneurysm, or subarachnoid hemorrhage and migraine) may show complete overlap in their symptomatic presentation.”
Dr. Croskerry adds that in these latter examples, the probability of correctly diagnosing the disease on the basis of clinical presentation may be no better than chance because noise may completely overlap the signal.
Diagnostic failure rates in modern hospitals approach 15%, a rate Dr. Pat describes as “staggering”.
In a 2011 study, for example, he and his team looked at factors contributing to what they called “abysmal diagnostic failure rates”. They studied patients who had been victims of “serious misdiagnoses” on a hospital’s internal medicine service. Here’s what they found:(1)
- 7% of diagnostic failures could not have been avoided (no fault)
- 28% – cognitive error only (error in the way the physician thinks)
- 19% – system-related (sent the wrong charts, mis-identified patient)
- 46% – a combination of both system-related and cognitive errors
Researchers concluded that the use of checklists could address many of these diagnostic failures:
“Diagnostic errors are common and can often be traced to physicians’ cognitive biases and mental shortcuts. A great deal is known about how these faulty thinking processes lead to error, but little is known about how to prevent them.
“Faulty thinking plagues other high-risk, high-reliability professions, such as airline pilots and nuclear plant operators – but these professions have reduced errors by using checklists.”
Surgeon-turned-author Dr. Atul Gawande has compared using checklists in medicine to a requirement that “house movers,wedding planners, and tax accountants figured out ages ago.”
As Dr. Croskerry’s team explained:
“Pilots do not have the option of skipping their checklists when the risk is low (sunny day, familiar airport, experienced crew). However, any recommendation to physicians to ‘use this checklist exactly when you think you don’t need it’ will likely be met with skepticism. “It would be tempting to use checklists only when we lack confidence in our diagnoses, but confidence is a poor predictor of diagnostic accuracy.”
In the 2011 research on diagnostic failure that Dr. Croskerry worked on, his team acknowledged some key differences between diagnostic checklists and those already well-accepted in aviation and industry.
In both medical and non-medical settings, for example, checklists are read aloud by teams rather than silently by individuals.
“But diagnosis is usually silent, lonely work, and a natural pause point to review the checklist, such as before takeoff or before incision, does not exist in diagnosis, which can stretch over hours, days or even months.”
Checklists have gained broad acceptance in medical settings such as operating rooms and intensive care units, but the 2011 study extended the checklist concept to diagnosing by providing an alternative to reliance on intuition and memory in clinical problem-solving.
“This kind of solution is demanded by the complexity of diagnostic reasoning, which often involves sense-making under conditions of great uncertainty and limited time.
“The key to reducing diagnostic errors may be less tied to checklists than to a diagnostic time-out – a brief pause to reflect on our diagnostic reasoning while reviewing a checklist and documenting the procedure in the medical record.”
* This cognitive reflective decision-making test was originally designed by Dr. Shane Frederick at M.I.T.*
(1) Checklists to Reduce Diagnostic Errors. Ely, John W. MD; Graber, Mark L. MD; Croskerry, Pat MD, PhD. Acad Med. 2011 Mar;86(3):307-13.
Q: Should diagnostic checklists be commonplace in medicine?
- When doctors can’t say: “I don’t know”
- Misdiagnosis: the perils of “unwarranted certainty”
- When your “significant EKG changes” are missed
- The ’18 Second Rule’: why your doctor missed your heart disease diagnosis
- Heart attack misdiagnosis in women
- Seven Ways To Misdiagnose a Heart Attack
- Doctors who aren’t afraid of “Medical Googlers”
- Experts: Why so wrong so often? from my other site, The Ethical Nag: Marketing Ethics for the Easily Swayed