Poor and incomplete data collection makes it difficult to know the full scope of people held in solitary confinement in U.S. prisons and jails. But a first-of-its-kind analysis is aiming to become a benchmark for tracking the practice — part of a larger effort as cities, states and the federal government weigh how to limit its use.

About 122,840 people in federal and state adult prisons and federal and local jails were placed in restrictive housing — informally known as solitary confinement — for 22 hours or more on a given day in mid-2019, according to a new report released Tuesday. That amounts to about 6% of the total U.S. prison and jail population at the time.