Scottish prison population statistics technical manual

Overview

This document contains information about the information presented in the Scottish Prison Population Statistics reports from 2019-20 onwards.

1. Data construction and implications
2. Analytical factors in cellWise statistics and their interpretation

Introduction to the prison population statistics

The prison population statistics are reconstructed from persistent information held on the Scottish Prison Service’s (SPS) prisoner records system (PR2). PR2 is a tool used by prison officers and administrators to understand and manage the current prison population day to day. As a result, it is not explicitly designed to be able to look back in time at the population as it was at any point in the past.

Previous Official Statistics relied upon the labour-intensive processing of daily snapshots, which were then strung together in such a way as to provide a longitudinal record. The vulnerability of this process was made evident when, in 2014, the data transfer of these snapshots broke down leading to a hole in the annual data collection.

In the absence of this continuous collection, the Official Statistics collection and publication schedule was discontinued. SPS stepped in to provide the basic aggregated information available to them as part of their management information platform. This was however limited by its initial settings to the information included when it was constructed. The outputs from that system continue, providing gender, age and legal status-based statistics on an annual basis.

From 2018, JAS analysts began seeking a better solution for providing transparency on a crucial subject for Scottish Ministers. A number of data models were attempted and compared against previous Official Statistics and the SPS Prison Populations. The chosen solution – cellWise – produced the closest match to available estimates.

The cellWise method is not a perfect picture of prison population over time. There are a number of innate issues with the design of the data, which is constrained by the information retained on PR2. Data sourced from PR2 itself are also inherently unstable, and liable to regular update and revision in the course of prisoner management.

As a result, we present a consistently compiled but “lower resolution” picture of the prison population. Nonetheless, if carefully used and interpreted, cellWise can provide a greater breadth and depth of information on the long-term trends to our user groups. 

The remainder of this document is intended to assist users in understanding the information they read in our Official Statistics reports or produce themselves in our interactive analytical tools.