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Lily pads on the surface of a lake double in surface area every 24 hours. If it takes 40 days for the lily pads to cover the lake completely, how many days does it take for half of the lake to be covered?

39 Days

If your answer changed before you submitted it , then you were able to successfully perform a forcing function to get to system 2 analytic thinking. Much like procedural time outs reduce operative errors, so too can “diagnostic time-outs.” Here’s a more relevant example:



















On first glance, you’d be forgiven for thinking STEMI or acute ischemia. But take a moment to look again the way you were trained to interpret ECGs – the way you train others to do. Is the left ventricular aneurysm more obvious now?
The trick with diagnostic time-outs is not to frame them in a way that biases the team toward the current diagnosis or management plan. What data goes for—and against—the diagnosis? What can—and can’t—be explained? This week, take time outs for a test drive and demonstrate for learners how questioning one’s own assumptions and decision making can positively impact patient care.


Croskerry P, Singhal G, Mamede S. (2013). Cognitive debiasing 1: origins of bias and theory of debiasing. BMJ Quality & Safety, 22 Suppl 2: ii58-ii64.

Croskerry P, Singhal G, Mamede S. (2013). Cognitive debiasing 2: impediments to and strategies for change. BMJ Quality & Safety,0:1-8.

Daniel M, Khandelwal S, Santen S, Malone M, Croskerry, P. (2017). Cognitive Debiasing Strategies for the Emergency Department. Academic Emergency Medicine,1:41-42.

Graber ML, Kissam S, Payne VL, et al. (2012). Cognitive Interventions to Reduce Diagnostic Error: A Narrative Review. BMJ Quality & Safety, 21:535-57.

Kahneman, Daniel. Thinking, Fast and Slow. (2011). New York: Farrar, Straus and Giroux.

Norman GR, Eva KW. (2010). Diagnostic error and clinical reasoning. Medical Education, 44(1), 94-100.

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