According to the 2006 Canadian Census, there were 1 159 405 people living in Peel Region. Peel contained a total of 207 CTs, 205 of which had both ethnicity information and cancer screening information available from the census. Peel is divided into three Census subdivisions: Caledon, Brampton and Mississauga.
We accessed information about Peel Region’s population eligible for health services and adults receiving cancer screening through a comprehensive research agreement with Ontario’s Ministry of Health and Long-Term Care. The research protocol was approved by the Research Ethics Board at Sunnybrook Hospital in Toronto.
Several databases were accessed for this study. Ontario’s health care registry, the Registered Persons Database (RPDB), includes all Ontario residents eligible for health coverage by age, sex and address. To be eligible for health coverage, one must be a Canadian citizen, permanent resident, or convention refugee, make one’s permanent and principal home in Ontario, and be physically present in Ontario for 153 days in any 12-month period. The Ontario Health Insurance Plan (OHIP) Physicians’ Claims Database contains claims for physician and hospital services and includes approximately 95% of physician claims in the province . The Ontario Cancer Registry is a registry of all Ontario residents who have been newly diagnosed with cancer or who have died of cancer. The Canadian Institute of Health Information Discharge Abstract Database contains fee codes and corresponding diagnostic codes claimed by Ontario’s physicians. Cytobase is Ontario’s electronic Pap test registry. The Ontario Breast Screening Program (OBSP) data record date of mammography for all women who participate in the province’s breast cancer prevention program. The Corporate Provider Database (CPDB) provides postal codes of primary care providers in the province.
Determination of rates of appropriate cancer screening by census tract
To determine cancer screening rates by CT, we used the RPDB to identify Peel residents eligible for breast, cervical and colorectal cancer screening based on provincial guidelines. Provincial guidelines by Cancer Care Ontario recommend that women aged 21–70 years be screened at least once every three years for cervical cancer, that women aged 50–69 years be screened at least once every two years for breast cancer, and that adults aged 50 years and over be screened at least once every two years for colorectal cancer.
Using postal codes from the RPDB, residents were assigned to specific 2006 CTs using Statistics Canada’s Postal Code Conversion File Plus . Anyone in the RPDB who had no contact at all with the health care system, including a physician office visit, hospitalization, emergency room visit, or drug benefit claim between April 1, 2008-March 31, 2011 was excluded, as these people are more likely to have died or moved out of the province. Across the screening cohorts (described below), an average of 6.5% of people were excluded due to lack of contact in the RPDB.
Eligibility for colorectal cancer screening was defined as being alive, living in Ontario, and 52–74 years of age on April 1, 2011. Anyone who had ever been diagnosed with colorectal cancer or severe inflammatory bowel disease was excluded. A total of 276 314 Peel residents were eligible. We used three definitions of appropriate colorectal cancer screening. People were considered appropriately screened if they had: i) FOBT between April 1, 2009 and March 31, 2011, or ii) colonoscopy between April 1, 2001 and March 31, 2011, or iii) sigmoidoscopy or barium enema between April 1, 2006 and March 31, 2011.
Eligibility for breast cancer screening was defined as being female, alive, living in Ontario and 52–69 years of age on April 1, 2011. Anyone who had ever been diagnosed with breast cancer was excluded. A total of 120 111 women were in this cohort. Women were considered appropriately screened if they had a mammogram between April 1, 2009 and March 31, 2011.
Eligibility for cervical cancer screening was defined as being female, alive, living in Ontario and 24–69 years of age on April 1, 2011. Anyone who had ever been diagnosed with cervical cancer, or who had any record of a hysterectomy or colposcopy, was excluded. There were 333 072 women in this cohort. Women were considered appropriately screened if they had a Pap test between April 1, 2008 and March 31, 2011.
Determination of ethnicity by census tract
2006 Census data were used to determine the ethnic origins of residents of each CT, namely, the proportion of residents of each CT who were identified as being of South Asian ethnicity. The South Asian region includes India, Pakistan, Bangladesh, and Sri Lanka.
Creation of maps
Two versions of each map were created. Choropleth (shaded) maps were used to depict the proportion of eligible adults in each CT who had each form of cancer screening (cervical, breast, colorectal), where the intensity of shading indicated the magnitude of screening. Circles were then overlaid, proportionate in size to the proportion of the population who identified as being of South Asian ethnicity.
Maps depicting results of Local Indicator of Spatial Association (LISA) analyses were also created. The LISA analysis used local Moran’s I indicator at the 0.05 significance level. These maps showed overlaid outcomes of two univariate LISA analyses, which identified clusters of high (or low) cancer screening rates and high (or low) percentages of South Asian populations.
In all maps, dots and stars, respectively representing locations of family physician practices and community health centres, were overlaid based on postal codes from the CPDB.