Imagine I tell you that a group of 30 engineers and 70 lawyers have applied for a job. I show you a single application that reveals a person who is great at math and bad with people, a person who loves Star Wars and hates public speaking, and then I ask whether it is more likely that this person is an engineer or a lawyer. What is your initial, gut reaction? What seems like the right answer?
Statistically speaking, it is more likely the applicant is a lawyer. But if you are like most people in their research, you ignored the odds when checking your gut. You tossed the numbers out the window. So what if there is a 70 percent chance this person is a lawyer? That doesn’t feel like the right answer.
That’s what a heuristic is, a simple rule that in the currency of mental processes trades accuracy for speed. A heuristic can lead to a bias, and your biases, though often correct and harmless, can be dangerous when in error, resulting in a wide variety of bad outcomes from foggy morning car crashes to unconscious prejudices in job interviews.
David McRaney writing in BoingBoing