Capital punishment information is collected annually as part of the National Prisoner Statistics program (NPS-8). This data series is collected in two parts: data on persons under sentence of death are obtained from the department of corrections in each jurisdiction currently authorizing capital punishment, and the status of death penalty statutes is obtained from the Office of the Attorney General in each of the 50 states, the District of Columbia, and the federal government.

NPS-8 covers all persons under sentence of death at any time during the year who were held in a state or federal nonmilitary correctional facility. This includes capital offenders transferred from prison to mental hospitals and those who may have escaped from custody. It excludes persons whose death sentences have been overturned by the court, regardless of their current incarceration status.

These statistics may differ from data collected by other organizations for various reasons: (1) NPS-8 adds inmates to the population under sentence of death not at sentencing, but at the time they are admitted to a state or federal correctional facility; (2) if inmates entered prison under a death sentence or were reported as being relieved of a death sentence in one year but the court had acted in the previous year, the counts are adjusted to reflect the dates of court decisions; and (3) NPS counts are always for the last day of the calendar year and will differ from counts for more recent periods.