c. n.a. 45.0 46.0 16.0 73.0   16th c. 7.0 25.0 21.0 11.0 47.0   17th c. 5.0 7.5 18.0 7.0 32.0   18th c. 1.5 5.5 1.9 7.5 10.5   19th c. 1.7 1.6 1.1 2.8 12.6   1900-1949 0.8 1.5 0.7 1.7 3.2   1950-1994 0.9 0.9 0.9 1.0 1.5     The steep decline of these numbers over the centuries suggests that, for one of the gravest human concerns-getting murdered-the incentives that we collectively cook up are working better and better. So what was wrong with the incentive at the Israeli day-care cen- ters? You have probably already guessed that the $3 fine was simply too small. For that price, a parent with one child could afford to be late every day and only pay an extra $60 each month-just one-sixth of the base fee. As babysitting goes, thats pretty cheap. What if the fine had been set at $100 instead of $3? That would have likely put an end to the late pickups, though it would have also engendered plenty of ill will. (Any incentive is inherently a trade-off; the trick is to balance the extremes.) But there was another problem with the day-care center fine. It substituted an economic incentive (the $3 penalty) for a moral incen- tive (the guilt that parents were supposed to feel when they came late). For just a few dollars each day, parents could buy off their guilt. Fur- thermore, the small size of the fine sent a signal to the parents that late pickups werent such a big problem. If the day-care center suffers only $3 worth of pain for each late pickup, why bother to cut short the ten- nis game? Indeed, when the economists eliminated the $3 fine in the seventeenth week of their study, the number of late-arriving parents didnt change. Now they could arrive late, pay no fine, and feel no guilt.