…Well, “plunge” is a real stretch. But I’m invoking alliterative license — four P’s in a row, zing! — to headline the news that the number of inmates in America looks to go down this year, for the first time since 1972.

Not surprisingly, it’s not because there are fewer crimes being committed:

Instead, the economic crisis forced states to reconsider who they put behind bars and how long they kept them there, said Kim English, research director for the Colorado Division of Criminal Justice.

In Texas, parole rates were once among the lowest in the nation, with as few as 15 percent of inmates being granted release as recently as five years ago. Now, the parole rate is more than 30 percent after Texas began identifying low-risk candidates for parole.

In Mississippi, a truth-in-sentencing law required drug offenders to serve 85 percent of their sentences. That’s been reduced to less than 25 percent.

California’s budget problems are expected to result in the release of 37,000 inmates in the next two years. The state also is under a federal court order to shed 40,000 inmates because its prisons are so overcrowded that they are no longer constitutional, [prison-issues advisor James] Austin said.

Not that a sub-one-percent drop in incarcerations is going to dent the U.S.’s distinction in having the largest prisoner population among the world’s nations — some 1.6 million people behind bars in Federal and State institutions. And I’m sure a re-crackdown on crime will gain steam as soon as recovery-fattened tax rolls are able to pay for it.

Still, it seems counter-intuitive that a slow economy would lead to fewer jailings. When business is bad, it gets bad all over, it seems.