How do we know when we’ve made the right generalization?

The always worth reading Malcolm Gladwell on “What pit bulls can teach us about profiling.” A short excerpt from an article more about decision-making than dogs:

Of course, not all pit bulls are dangerous. Most don’t bite anyone. Meanwhile, Dobermans and Great Danes and German shepherds and Rottweilers are frequent biters as well, and the dog that recently mauled a Frenchwoman so badly that she was given the world’s first face transplant was, of all things, a Labrador retriever. When we say that pit bulls are dangerous, we are making a generalization, just as insurance companies use generalizations when they charge young men more for car insurance than the rest of us (even though many young men are perfectly good drivers), and doctors use generalizations when they tell overweight middle-aged men to get their cholesterol checked (even though many overweight middle-aged men won’t experience heart trouble). Because we don’t know which dog will bite someone or who will have a heart attack or which drivers will get in an accident, we can make predictions only by generalizing. As the legal scholar Frederick Schauer has observed, “painting with a broad brush” is “an often inevitable and frequently desirable dimension of our decision-making lives.”