ONE MIGHT HAVE expected that with a few years of an underperforming economy, crime -- which has dropped precipitously over the past decade -- would have begun ticking up again. Yet new data from the Justice Department's National Crime Victimization Survey suggest otherwise. Violent and property crime in 2003 remained essentially unchanged from the previous year: that is, at the lowest levels since the survey began in 1973 and at roughly half the level of the early 1990s. This particular survey excludes murders, which increased by about 1 percent between 2002 and 2003, and property crime nudged up insubstantially during that time. But violent crimes other than murder declined marginally. In other words, while the steep decline in crime appears to have leveled off, there is little sign that the gains the United States made were a mere gift of a humming economy. That fact, however, only raises the question of what has caused this dramatic change in American life and how policymakers can make it last.

Unfortunately, nobody really knows the answer to these questions with any precision, and much discussion of them is too political to be of much use. Conservatives point to longer prison sentences that have landed more than 2 million people behind bars in this country. Some Democrats point to the tens of thousands of new police officers hired during the Clinton administration. Both of these probably had an impact, yet it is far from clear that the drop is chiefly a function of policy at all. The waning of the crack cocaine epidemic probably played a significant role, as did demographic trends, which reduced the number of young men as a percentage of the population, and there was the backdrop of the strong economy.

Identifying the key factors in a social phenomenon influenced by so many variables necessarily involves a measure of guesswork. But it is important to have a better sense of the effectiveness of some of these policies, because the costs have been staggering. While increasing prison time has probably had an impact, having 2 million Americans locked up -- many for nonviolent offenses -- has taken an enormous human, financial and moral toll on the country. The imprisonment of a group of people that rivals in magnitude the combined populations of a few of the smaller states is not the only possible way to hold down crime. Yet even as prisons have grown, other crime-fighting strategies have gotten short shrift: Guns remain pervasively available, while drug treatment, which costs a fraction of the price of incarceration, is far less so. While it is tempting to assume that dramatic policy changes must have caused the decline in crime, it's worth asking whether a more humane strategy would have produced the same -- or maybe even better -- results.