In order to fill the data gap, a linkage of the Census 2006 to hospital information included in the Discharge Abstract Database (DAD) from the Canadian Institute for Health Information (CIHI) was undertaken. This was to investigate the hospitalization patterns among key subgroups (e.g., Aboriginal groups, immigrant groups and older adults) in order to fill the existing data gap. In addition, the linked data will provide researchers the opportunity to investigate those characteristics that place individuals at higher risk of using hospital services. Identifying and documenting the differences in patterns of health services utilization will provide evidence for policy makers and health care planners.
In order to investigate hospitalization patterns among key subgroups, a linkage between the Census 2006 and the Discharge Abstract Database (DAD) was performed. This linkage included the long form component of the 2006 Census of the Population and three fiscal years of DAD data (2006/2007 to 2008/2009). Residents of Quebec were excluded.
2006 Census of the Population
The 2006 Census, which included both a short- and long-form questionnaire, was used in this linkage project. Approximately, 80% of households received only the short-form questionnaire which included information on date of birth, sex and marital status of all household members. The remaining 20% of households received both the short- and long-form questionnaire. The long-form included questions related to education, ethnicity, mobility, income and employment. The Census represents 95 to 97% of the population in the provinces and 93 to 94% of the population in the territories.
For the purpose of this linkage project, only those respondents who completed the long-form questionnaire were included in the linkage study cohort and Quebec residents were excluded from the Census cohort due to a lack of corresponding hospitalization data. For specific details about the in-scope 2006 Census population used in this linkage please consult Rotermann et al. 1
Detailed information about the Census, including the Census dictionary and references, the questionnaire and the codebooks (with or without frequencies), as well as various technical reports are available to RDC researchers. For more information please speak to your RDC analyst.
Discharge Abstract Database (DAD)
The Discharge Abstract Database (DAD) captures administrative, clinical and demographic information on hospital discharges (including deaths, sign-outs and transfers) from all provinces and territories, except Quebec. Over time, the DAD has also been used to capture data on day surgery, long-term care, rehabilitation and other types of care.
In the DAD, jurisdiction-specific instructions for collection of data elements evolve over time. Collection of each data element may be mandatory, mandatory if applicable, optional or not applicable. Collection requirements can vary by jurisdiction and by data year.
Researchers will find the listings of DAD data elements under the heading “Data Elements” at the DAD Metadata website. Please note that not all DAD data elements are included in the RDC DAD datasets for this linkage project. A list of available DAD variables is contained in Appendix A. The documents on the website include information on mandatory versus optional collection status for each data element by jurisdiction, which is key to understanding coverage of data elements in the DAD.
For this record linkage, DAD data from the fiscal years 2006/2007 to 2008/2009 were included, representing 9,623,313 hospitalization records (3,186,079 in 2006/2007; 3,204,838 in 2007/2008 and 3,232,396 in 20087/2009). For specific information about the in-scope DAD population used in this linkage please consult Rotermann et al. 1
File structure, layout
The 2006 Census File was modified for this project to provide a file for researchers that includes only those records that were eligible for linkage (e.g., Quebec residents excluded). This Census 2006 Cohort file includes a unique identifier variable called Person_ID that researchers will use to merge to each year of the DAD. Not all records in the Census cohort have a link in the DAD.
Users should note that 101 institutional records included in the original Census 2006 cohort are not included in the Census file available in the RDCs. The Census 2006 cohort for the RDC contains 4,652,582 records. The corresponding DAD records which had been linked to these Census records are also not included in the DAD files provided to the RDC for this linkage.
Researchers should consult the Census documentation (available from your RDC analyst) to obtain detailed information about the Census variables.
The DAD is an event based file meaning that there will be more than one record for a person who was hospitalized more than once in the same fiscal year. During the linkage process, all records belonging to one person were identified and a unique linkage key for that person, inclusive of all hospital events, was created. This allows the researcher to identify individuals with multiple hospitalizations. Researchers can then choose to use the DAD file as an event based file (each row of data represents a hospitalization) or a person based file (each row of data represents an individual).
In order to use the file as a person based file, the researcher must transform the data to include all hospital information for one person as one record (one row on the data file).