Study Design
We conducted a population-based retrospective cohort study of home care clients in the provinces of Ontario and Alberta, and in the regions surrounding Winnipeg, Manitoba and Whitehorse, Yukon.
Data Sources
We linked multiple, anonymized, administrative health databases to construct our cohort. Home care clinical assessment data was extracted from the Home Care Reporting System, a national database that contains demographic, clinical, functional and service utilization information on publicly funded home care clients in Canada. Emergency department utilization data were extracted from the National Ambulatory Care Reporting System, which houses comprehensive data on hospital and community-based ambulatory care visits in Canada. The databases used in this study are routinely checked for validity and have been extensively used in health services research.18-22 We received ethics approval from the Hamilton Integrated Research Ethics Board.
Participants
Home care clients in Canada are periodically assessed using the Resident Assessment Instrument for Home Care (RAH-HC). We created a retrospective cohort of all RAI-HC assessments completed between April 1, 2011 and September 30, 2014. Data were accessed on clients in the provinces of Ontario and Alberta. as well as in the Winnipeg Regional Health Authority in Manitoba and in the Whitehorse census subdivision of the Yukon Territory. The cohorts in Manitoba and Yukon were restricted to areas surrounding the cities of Winnipeg and Whitehouse due to limitations in the coverage of the National Ambulatory Care Reporting System. The RAI-HC assessments in the cohort were linked to emergency department records to identify all ED visits within six months of the assessment date.
Measurement.
The DIVERT scale was developed through the use of recursive partitioning on the assessment items of the RAI-HC. The RAI-HC is a comprehensive clinical assessment of over 250 items that have demonstrated validity and reliability in documenting the domains of function, health, social support, and health service use.22,23 The RAI-HC is currently used for standardized home assessments in most Canadian provinces and territories, half of U.S States, and in many countries around the world including: Estonia, Finland, Hong Kong, Iceland, Ireland, Italy, Japan, The Netherlands, New Zealand, Singapore, Spain, and Switzerland. At this time, the DIVERT scale has been implemented as a standard scale within the RAI-HC assessment.
Outcome Measure. The primary outcome of this study was an ED visit within 6 months after a RAI-HC assessment date. Secondary outcomes include: (a) two or more ED visits within 6 months of a RAI-HC assessment, and (b) any ED visits that resulted in a hospital admission. Data were censored at date of death. All outcomes were selected to parallel the figures in the original derivation study.14 A 6-month follow-up period was chosen to reflect the contemporary home care assessment intervals.
Data Analysis
The DIVERT scale was derived and validated using home care assessment data linked to ED records from Ontario and Winnipeg between 2006 and 2010.14 Our examination of data from Ontario, Alberta, Winnipeg, and Whitehorse between 2011 and 2014 enables us to test of the scale’s validity within the two original regions, but also at a later time period validating the temporality of the predictions. We measured the predictive ability of the DIVERT scale using the area under the receiver operating curve (AUC), or c-statistic. The AUC is the area under the curve created by plotting sensitivity against 1-specificity at various thresholds and is a common measure of the discriminative ability. Within each region, we calculated the AUC of the DIVERT scale for each outcome. All analysis was performed using SAS/STAT 13.1.