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Prison Population

Background to Publication Delay

The delay in publication of the ‘Northern Ireland Prison Population’ series from 2011 onwards followed the discovery of a data anomaly in receptions information published in the ‘Northern Ireland Prison Population in 2009’. Specifically, information for prison receptions relating to the year 2009 in Tables 7-12 of that publication are not to be considered reliable. These figures represented a clear discontinuity with the data series for the years 2000-2008.

The source of this discontinuity for reception information was established as being the transition to a new and improved information management system (PRISM) within the Northern Ireland Prison Service, which became the source of statistical information for this publication for the first time for the calendar year 2009. It can be seen from the published 2009 data that the numbers of receptions were given as decreasing, in some cases dramatically, at a time when numbers on the whole were increasing. The reason for this was that the validation conducted on the dataset for the publication had failed to identify that in the process of migration to the new system, the traditional statistical base fields of the Custody History Section had not always been fully populated.

It was quickly established that there were no grounds for considering reception figures in these tables relating to the earlier years (2000-08) as other than reliable. Nor were there any grounds for doubting the accuracy of figures relating to average population itself, as contained in Tables 1-6 and related text.

Latest Developments

Since the introduction of this new system considerable work has been carried out to ensure that full custodial history for each prisoner can be analysed. Following on from this, a statistical mechanism has also now been derived to enable the compiling of statistics on receptions for each prisoner based on comparison of changes in daily snapshot information on prisoner population (i.e. to derive prisoner flow information from an analysis of daily changes in population stocks).

A pilot test of this mechanism was undertaken in December 2013 and further refinements were subsequently implemented leading to a successful validation exercise carried out in March/April 2014. Since that point competing priorities in prison population work have impacted on the planned timescale for producing retrospective receptions information. Subject to currently known (i.e. July 2014) priorities, the intention would be that receptions figures for the years 2009-2012 inclusive will now be published at end September 2014.

Population bulletins

Your views sought

A series of detailed consultation exercises of known and potential users of prison statistics were undertaken in late 2013 and early 2014 to identify the preferred longer-term structure and format of publications. If you would be interested in inputting additionally in contributing your views, have any other comments you would wish to make or would simply like to register interest in being informed of further publications, please Contact us.