A wee bit of good news about American prisons for a change: after rising each year since the mid-1970s, the US incarceration rate has declined each of the past three years.

I hereby submit my nomination for the most underreported public policy story of the past year: The continuing decline in the number of Americans who are behind bars or on probation/parole. Both the change itself and low level of attention it has garnered are worthy of reflection.

At the time of President Obama’s inauguration, the incarceration rate in the United States had been rising every single year since the mid 1970s. The relentless growth in the proportion of Americans behind bars had persisted through good economic times and bad, Republican and Democratic Presidents, and countless changes in state and local politics around the country.

If a public policy trend with that much momentum had even slowed significantly, it would have been merited attention, but something far more remarkable occurred: The incarceration rate and the number of people under correctional supervision (i.e., including people on probation/parole) declined for three years in a row. At the end of 2011, the proportion of people under correctional supervision returned to a level not seen since the end of the Clinton Administration.