Geographic methods for understanding and responding to disparities in mammography use in Toronto, Canada

Abstract

Objective: To use spatial and epidemiologic analyses to understand disparities in mammography use and to formulate interventions to increase its uptake in low-income, high-recent immigration areas in Toronto, Canada.

Design: We compared mammography rates in four income-immigration census tract groups. Data were obtained from the 1996 Canadian census and 2000 physician billing claims. Risk ratios, linear regression, multilayer maps, and spatial analysis were used to examine utilization by area for women age 45 to 64 years.

Setting: Residential population of inner city Toronto, Canada, with a 1996 population of 780,000.

Participants: Women age 45 to 64 residing in Toronto's inner city in the year 2000.

Measurements and main results: Among 113,762 women age 45 to 64, 27,435 (24%) had received a mammogram during 2000 and 91,542 (80%) had seen a physician. Only 21% of women had a mammogram in the least advantaged group (low income--high immigration), compared with 27% in the most advantaged group (high income--low immigration) (risk ratio, 0.79; 95% confidence interval, 0.75 to 0.84). Multilayer maps demonstrated a low income-high immigration band running through Toronto's inner city and low mammography rates within that band. There was substantial geographic clustering of study variables.

Conclusions: We found marked variation in mammography rates by area, with the lowest rates associated with low income and high immigration. Spatial patterns identified areas with low mammography and low physician visit rates appropriate for outreach and public education interventions. We also identified areas with low mammography and high physician visit rates appropriate for interventions targeted at physicians.

FIGURE 1

Choropleth (shaded) map of census tracts showing distribution of income and immigration groups in Toronto's inner city, 1996.

FIGURE 2

Proportional symbol map of women with mammograms (circles) in relation to choropleth (shaded) layer of income and immigration group by census tract in Toronto's inner city.

FIGURE 3

Moran's scatterplot of proportion of women with mammograms (2000).

FIGURE 4A

Proportional symbol map of women needing a mammogram (circles) in relation to an interpolated grid layer (background shading) of women without an ambulatory care visit by census tract in Toronto's inner city.

FIGURE 4B

Dot density map of number of women needing a mammogram (dots) in relation to an interpolated grid layer (background shading) of women without an ambulatory care visit by census tract in Toronto's inner city.