The data for the Incentives and Earned Privileges Scheme (IEPS) is recorded on the Prison Service management information system (PSIMON). PSIMON is independent of the system recording population data, this is why there is a shortfall against the published population data. The information is only used to provide indicators for monitoring, and at a national level, the operation of the system.
The variation between the totals of reported IEP levels and the population summary is due to the two sets of data being recorded at different times. There may also be an element of misreporting.
Copies of the requested data have been placed in the Libraries of the House.