Data sources, methods, and limitations

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Data sources

Canadian Community Health Survey

Data from the 2000/2001 Canadian Community Health Survey (CCHS) (cycle 1.1) were linked to the Hospital Morbidity Database (HMDB) (2000/2001 to 2004/2005). The CCHS collects cross-sectional information about the health and health care use of Canadians. The survey covers the non-institutionalized household population aged 12 or older in all provinces and territories, except members of the regular Canadian Forces and residents of Indian reserves, Canadian Forces bases (military and civilian) and some remote areas. A description of the methodology has been previously reported.¹⁸ The overall response rate in 2000/2001 was 85%; the total sample numbered 131,535. Insufficient information was available in the hospital data for Quebec residents' records to be linked (see Hospitalization data); therefore, the 22,667 (17%) CCHS respondents in Quebec were dropped from this analysis. Of the 108,868 respondents who remained, 90,450 had given permission for their survey data to be linked to administrative data. Check-digit algorithms were used to verify the plausibility of the health numbers they provided; 72,363 provided a plausible health number required for data linkage.

Hospitalization Data

Statistics Canada's Hospital Person-Oriented Information Database (HPOI) is a person-level dataset derived from discharge records of inpatients in most of the acute care hospitals and some psychiatric, chronic and rehabilitation hospitals.¹⁹ The discharge records contain demographic (gender, date of birth, postal code), administrative (health number, admission and separation dates) and clinical information derived from the the Hospital Morbidity Database (HMDB) maintained by the Canadian Institute for Health Information.²⁰ During data processing at Statistics Canada, about 3% of HMDB records for patients aged 12 or older were excluded because of missing or invalid health numbers. The HPOI represents approximately 3.4 million inpatient acute care admissions each year.

Linking health survey and hospital data

The survey and administrative data were linked at the individual level using probabilistic linkage methodology.  Unique identifying information including health number, postal code, date of birth and age were used in the linkage. Linkage was conducted only for CCHS respondents living outside Quebec who provided consent to link their survey data to other sources of health information. The linkage was conducted by Statistics Canada. Additional information about the process is provided elsewhere.²¹ A recently published evaluation of the linkage between the CCHS and HPOI reported high coverage for the population younger than age 75.²²

Methodology

Sample

The study sample consists of CCHS respondents aged 12 to 74 (excluding Quebec residents) who gave permission to have their survey data linked to the HMDB and who indicated that they have been diagnosed with at least one of the following ACS conditions:  asthma, emphysema/ chronic obstructive pulmonary disorder (COPD), diabetes, epilepsy, heart disease or high blood pressure (n=16,931; N=2.75 million). CCHS interviews were conducted from September 1, 2000 to November 3, 2001. Starting from the date of the CCHS interview, linked hospital records were searched prospectively for four years (1,462 days) for each respondent. Individuals were then "followed" over time in the linked hospital administrative data to determine if they experienced one of the following events:  at least one ACSC-related hospitalization admission (n=840); at least one other type of hospitalization (n=4,149); or no hospitalization (n=11,942). Censoring before the end of the four-year period to account for events such as death or moving out of the province was not possible because information about these events was not available or incomplete.

ACSC-related hospitalizations were defined as acute care inpatient hospital admissions for angina, asthma, COPD, diabetes, grand mal status and other epileptic convulsions, heart failure and pulmonary edema and hypertension. ICD9/10 codes listed as the "most responsible" diagnosis were used to identify ACSC-related admissions in accordance with methodology developed by the Canadian Institute for Health Information (see Appendix A).

Table A
Selected characteristics by hospital admission status, household population aged 12 to 74 with ambulatory care sensitive conditions (ACSCs), Canada excluding Quebec, 2000/2001

Analytical techniques 

Descriptive analyses were conducted to estimate the prevalence of various demographic, socio-economic, health status and health care use indicators using the SAS software (version 9.1).  Prevalence estimates were adjusted to the nationally representative sample of individuals aged 12 to 74 with an ACS condition, as defined in the 2000/2001 CCHS.  Bivariate logistic regressions (weighted; adjusted for age and sex) were conducted to identify factors significantly associated with experiencing at least one ACSC-related hospitalization in the four-year period following the survey.  Separate analyses were conducted to compare individuals with an ACSC-related hospitalization to: 1) those who experienced at least one other type of hospitalization; and 2) those with no hospitalizations.  (Results are provided in the Appendix Tables B and C). Gender-specific multivariate logistic regression analyses were conducted to consider the full range of patient and primary care factors associated with ACSC-related hospitalizations.  Only factors that were significant in the bivariate analyses were selected.  The stepwise technique was applied to ensure selection of a parsimonious list of factors.  The multivariate analyses were conducted using SAS-callable Sudaan (version 9.1.3).

Table B
Age/sex adjusted odds ratios relating selected demographic, socio-economic, health status, health behaviour and health care experience characteristics to ACSC-related hospitalizations versus no hospitalizations, household population aged 12-74 with ambulatory care sensitive conditions, Canada excluding Quebec, 2000/2001

Table C
Age/sex adjusted odds ratios relating selected demographic, socio-economic, health status, health behaviour and health care experience characteristics to ACSC-related hospitalizations versus non-ACSC related hospitalizations, household population aged 12-74 with ambulatory care sensitive conditions, Canada excluding Quebec, 2000/2001

The bootstrap technique was applied to all analyses to account for the complex survey design and to estimate variance and confidence intervals.  Survey weights were specifically produced by Statistics Canada for the linked file to adjust for non-response to the CCHS and for the exclusion of records of respondents who did not provide plausible health numbers or give permission for linkage to administrative data.  These weights were applied to the analysis file. The weighted data were representative of the Canadian household population residing outside Quebec.

Independent variables

A comprehensive set of patient characteristics was considered to assess the association with ACSC-related hospitalizations.  Variables were derived from the CCHS survey data and grouped in the following categories: demographic (age, sex, rural/urban status, race), socio-economic status (household income, education, family/marital status, immigration status), health status (self-reported health, disability level, presence of co-morbidities, self-reported daily stress, impact of health problems, pain), health behaviours/risk factors (smoking status, body mass index (BMI), physical activity index, fruit and vegetable consumption, community belonging), and access to health care services (access to regular medical doctor, use of family physician and specialist services, hospitalization, unmet healthcare needs) (see Appendix Table A for complete list of variables).

Limitations

• While the use of population-based health surveys provides the opportunity to assess ACSC-related hospitalizations among those "at risk" (with an ACS condition), the generalizability of the results is restricted to the household population aged 12 or older.   Consequently, the results do not necessarily represent the experiences of the very young or the institutionalized population.

• Selection of the sample was based on self-reported information provided in the CCHS about an ACS condition that had been diagnosed by a health care provider, and that had lasted or was expected to last more than six months.  This information has not been clinically validated.

• Information about disease severity was not available.  General health status measures, such as self-reported health, disability level and co-morbidities, were used as proxy indicators.   

• The CCHS information about the primary care experiences of respondents is limited.  Thus, access to primary care was based on information about access to a regular medical doctor and volume of family physician visits.  The study cannot address the role of the type or quality of primary care in ACSC-related hospitalizations nor assess the appropriateness of service use.