Prison sentences are getting shorter. But racial disparities are getting worse.

There's good news and bad news about sentences in federal prison. The good news: Prison sentences are getting shorter. The bad news: Black defendants are still getting longer sentences than white ones for the same crimes — and the racial gap is actually growing.

That's the conclusion of a new study conducted for the Bureau of Justice Statistics, based on data from 2005 — after a Supreme Court decision gave judges more flexibility in sentencing — through 2012. But it's certainly not the first study to find that even when...