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Study Points to Cognitive Bias in Medical Decision-making

In This Article

  • A recent study published in the New England Journal of Medicine found that heart attack patients two weeks after turning 80 years old are less likely to receive bypass surgery than those two weeks short of the same age
  • A common cognitive bias, called the left-digit bias, leads to individuals focusing on the first number in a sequence, perceiving a larger difference between two numbers
  • This bias may play a part in medical decision-making on the basis of age

A study published in The New England Journal of Medicine, led by Anupam Jena, MD, PhD, clinician in the Department of Medicine at Massachusetts General Hospital and associate professor of health care policy and medicine at Harvard Medical School, found that heart attack patients who had turned 80 in the last two weeks were less likely to get bypass surgery than patients who were two weeks shy of that same age.

Dr. Jena and his team studied Medicare records from 2006 to 2012 on 70,000 heart attack patients. Ten thousand of those patients were within two weeks of their 80th birthday. The study found that 5.3% of patients who had turned 80 two weeks prior received bypass surgery, while 7% of patients who were two weeks from their 80th birthday received the same surgery.

Other age differentials were examined and no such differences in rates were found. This data suggests that the 80-year-old mark is a significant one when determining risk for bypass surgery. However, patients over the age of 80 have higher death rates during the first two months after a heart attack, meaning those patients are the ones more in need of the surgery.

One Explanation: The Left-digit Bias

Dr. Jena and his team point to the "left-digit bias" to explain the perception that it is less risky to perform bypass surgery on a 79-year-old versus an 80-year-old, even when the actual age difference is less than one month. This psychological bias is the tendency to focus on the first number that appears in a sequence. It is commonly used to explain purchasing behavior—for example, individuals are more likely to purchase an item priced at $4.99 than at $5. The left-digit bias may subconsciously be playing a part in medical decision-making on whether or not to perform a surgery. In Everyday Health, Dr. Jena notes that while doctors might not be able to eliminate every bias, being aware of the existence of this bias is a good start to improving care.

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