I remember the story of "9-enders" (aged twenty-nine, thirty-nine, fifty-nine) who are much more enthusiastic to run their first marathon. In many ways, the left-digit bias reinforces our tendency to categorize continuous variables on the basis of the left-most numeric digit.

The susceptibility of our brains to fall into the trap of heuristics or hard-wired mental shortcuts is common. It can affect many of us. And we (and by we I mean runners, customers, parents, and doctors) tend to be affected without being aware of the cognitive biases.

Hey, I just found out doctors are also making clinical decisions with left-digit bias. For those of you who think high-tech physicians are awesome in calculating the risk-benefit trade-off to manage patients with acute heart attack, go and read the recent issue of the New England Journal of Medicine . Based on data of patients who were admitted to hospital with acute myocardial infarction over six years, those admitted in the 2 weeks after their 80th birthday were significantly less likely to undergo bypass surgery than those who were admitted in the 2 weeks before their 80th birthday.

The creepy reason of your being turned down for a life-saving heart surgery, in short, could have simply been the way you're categorized as being "in your 80s" rather than "in your 70s", and that, in turn, is a matter of few weeks' difference in your birthday.

Amen.