5.1 Method
As set out in section 2.2, the MHDCD Dataset is made up of a cohort of 2,731 individuals who have been in prison in New South Wales and whose mental health disorder and cognitive disability diagnoses are known. The MHDCD cohort is drawn from the NSW Inmate Health Survey (2001, 2009) and the NSW Corrective Services Statewide Disability Service database. Using linked but de-identified extant administrative records from criminal justice and human services agencies in NSW, the Dataset allows for the building of multilevel analysis of the experiences of this cohort through their contact with criminal justice and human service agencies. Each individual in the cohort was matched in each agency and all matches for each person for that agency were added to the database as an agency-specific subset. The data linking and matching took place in 2010 but with considerable reanalysis over the following two years to address anomalies that emerged as the data were merged.
There were significant barriers in achieving this linkage. For example, it was not possible to gain consent from all those in the potential dataset due to likely incapacitation of many and lack of information as to their present whereabouts. Advice was sought from the NSW Privacy Commissioner who ruled the public benefit outweighed the risk of identification of individuals. The project team was given permission from each ethics body to draw and link the data ensuring strict privacy and confidentially of the data. As the initial data was being drawn it became clear that some in the dataset had numerous aliases, some as many as 50. Altogether the average for aliases was 10 per person. This meant that it was not possible for standard linkage keys to be used to ensure the right person in each dataset was matched. Problems with aliases and incorrect individual matching were found even in the internal data from Courts, Police and Corrective Services. The project team had to develop a cascade of verifying methods in order to be certain the right individual was linked with his or her data in each dataset.
The method allowed for the linking of data related to each individual from any subset with any other subset, which enabled the creation of specifically compiled subsets of interest, overall administrative de-identified lifecourse ‘pathway’ case studies for individuals in the dataset, aggregated subset pathways and patterns of effects of agency interactions with individuals, subgroups and other agencies. Linking data across the criminal justice sub-systems and with relevant human services provides a broad, dynamic, trans-criminal justice and human service understanding of the involvement of vulnerable people in the criminal justice system.
Initial analyses indicated that Indigenous persons in the cohort had a higher rate of multiple diagnoses and disability. This provided the imperative for seeking to undertake further quantitative investigation of the pathways and experiences of Indigenous persons with MHDCD in the CJS.
