antiselection in health

Imagine an insurer offers a health plan at one price to anyone who wants it, no questions asked. Who rushes to buy? Disproportionately the people who already know they will need care — someone planning surgery, managing a chronic condition, or expecting a baby. The healthy may wait or skip it. This tilt, where those most likely to claim are the most eager to buy, is antiselection, and it is the quiet force that can unravel a health plan.

Antiselection happens whenever buyers know more about their own risk than the insurer can price for, and act on it. The mechanics are a vicious circle: if the sick buy more than the healthy, claims exceed the premium, so the insurer raises the price; the higher price drives out the healthiest remaining members first (they value the cover least); the pool gets sicker still; the rate rises again. Left unchecked this can spiral toward collapse — sometimes called a death spiral. In health it shows up in many guises: people buying just before a planned procedure, choosing richer plans because they expect to use them, or dropping cover once healthy.

Fighting antiselection is central to health-actuarial and product design. The classic tools are medical underwriting (asking health questions and pricing or declining accordingly), waiting periods and pre-existing-condition limits, enrollment windows so people cannot buy only when sick, and incentives or mandates that bring healthy people in to balance the pool. Where regulation forbids underwriting (community rating with guaranteed issue), antiselection must be offset some other way — broad participation, risk adjustment between insurers, or subsidies — or premiums climb for everyone. Recognizing where a design leaks selection is one of the most valuable instincts a health actuary has.