But the number is probably far higher, Marshall Project survey shows. Among the millions of people incarcerated in the United States, a significant portion have long been thought to be parole violators, those who were returned to prison not for committing a crime but for failing to follow rules: missing an appointment with a parole officer, failing a urine test, or staying out past curfew. But their actual number has been elusive, in part because they are held for relatively short stints, from a few months to a year, not long enough for record keepers to get a good count. To help fill the...