The “metrics” system
If you would like to produce good quantitative social-science research, try remembering these two words: “ceteris paribus.” That’s Latin for “other things being equal.” And it’s a key principle when designing studies: Find two groups of people who, other things being equal, are distinguished by one key feature. Consider health care. If you can find two otherwise equal groups of people who differ only in terms of health care coverage — one group has it, one doesn’t — then you may be able identify a causal relationship at work: What difference does it make when people get health insurance? Without such a research strategy, scholars can be left staring at a tangle of potential causes and effects. Suppose you have one group of people with health insurance, and one without — but the insured people are wealthier. Are they better off financially because they have insurance, or do they have insurance because they’re...