Data and Mapping Notes

Data for the maps included in the health component of the Atlas of Canada have been acquired initially at several levels of details. Rates or other measures are then computed and displayed as choropleth maps (maps where predefined areas are shaded to illustrate a specific value or range of values that apply to the respective geographical unit).

The primary geographical units that are employed are "census divisions" and "health regions".

• Census Division (CD) is the general term applied to areas established by provincial law which are intermediate geographic areas between the municipality and the province levels. Census divisions represent counties, regional districts, regional municipalities and other types of provincially legislated areas. In Newfoundland, Manitoba, Saskatchewan and Alberta, provincial law does not provide for these administrative geographic areas. Therefore, census divisions have been created by Statistics Canada in cooperation with these provinces for the dissemination of statistical data. In the Yukon Territory, the census division is equivalent to the entire Territory. (Source: Statistics Canada). For the 1991 Census of Population, 290 census divisions existed. In 1996, 288 census divisions were defined. Nunavut did not exist at the time of the 1991 or 1996 Census as the territory was only created in April of 1999. For the maps based on CDs, Northwest Territories includes Nunavut.
• Health Region (HR) refers to a geographic unit defined by a provincial health ministry. It usually represents the area of responsibility for a regional health board or authority. In Saskatchewan, health regions are called "health districts" and "service areas"; in Ontario, "district health councils" and "public health units". (Source: Statistics Canada). For the analysis of Canadian health statistics, 139 health regions have been defined for the entire country.

The choropleth mapping technique is sometimes limited in use when displaying data for the large areas in the northern and rural regions which contain small and widely scattered populations. Consequently, the measures that have been calculated at the census division or health region level of geography are displayed using the concept of the population ecumene.

• Population Ecumene generally refers to land where people have made their permanent home and to all work areas that are considered occupied and utilized for agricultural or any other economic purpose (Statistics Canada).

Methodological Note (Nursing)

For many administrators and researchers involved with nursing workforce issues, the primary source of information is the Registered Nurses Database (RNDB) held by the Canadian Institute for Health Information (CIHI). CIHI gathers information about registered nurses (RNs) from the various provincial and territorial nursing associations across Canada. And they regularly generate population-to-nurse ratios for the country as a whole and for provinces/territories.

Even for CIHI, the computation of population-to-nurse ratios (number of people within a given geographical region divided by the number of nurses in that same area) is not always straight forward. In terms of the numbers of nurses, CIHI eliminates duplicate records (i.e. some nurses are registered with more than one provincial/territorial association) and also eliminates nurses not currently employed in nursing. In terms of population numbers, CIHI uses actual census counts for census years or Statistics Canada estimates for years between the Census (which occurs every five years only). Difficulties arise because these estimates may not be totally accurate and/or data from the registered nurses may not be complete. Sub-provincial population-to-nurse ratios, which would be desirable for use in the Atlas but that CIHI does not compute, suffer greatly because of these enumeration problems.

Another source of information about nurses in Canada is the actual Census of Population. Population-to-nurse ratios can be computed for census years with confidence in terms of the population numbers (actual rather than estimates). Included in that enumeration is a count of Canadians by occupations, one category of which is "Nurse Supervisors and Registered Nurses". But this count includes registered nurses who may not be employed in nursing. Ratios computed with those counts of nurses will not match with those reported by CIHI.

In 1996, 86.5% of the total number of registered nurses in Canada were employed in nursing. This proportion was applied to the 1996 census occupation category at the census division level to produce the sub-provincial population-to-nurse ratios that are mapped in the Atlas:

Population-to-Nurse Ratio = (1996 census population count) / ((1996 census nurses count) * .865)

Figure 1 compares this approach with the national and provincial/territorial ratios. Overall, the match is very good with only slight over estimations for most jurisdictions. The exceptions to this observation are for the Northwest Territories and Newfoundland where the over estimations are significant. However, the broad mapping classes that have been employed are believed to reflect the distributional pattern of population-to-nurse ratios accurately, if not precisely.

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Figure 1. Comparison Between 1996 CIHI Computed and Census Imputed Population-to-Nurse Ratios

Standardization of Rates: A Methodological Note

In general, many diseases show a strong relationship with age and often with gender. Crude incidence or mortality rates may therefore be misleading when comparing regions or time periods where the age- and or sex-composition of the populations differ from one region to another or from one time period to another.

• "Standardized" (by age, sex, or age-sex) Rates can be calculated to adjust for these age-sex compositional differences in populations. The calculations of these rates are somewhat complex where the specific region (or period of time) rates are compared with a standard or reference population. Many disease rates (including the breast cancer incidence rates used in the Atlas) in Canada are standardized by the age distribution characteristics of Canadians in 1991. Essentially, age-standardized rates allow one to answer the question "Suppose these populations have the same age distribution, how would their overall experience with this disease compare?" (Valanis, 1992).
• Age-Standardized Ratios further aid in regional comparisons. These are often computed by dividing the age-standardized rate for a particular region by the rate for the geographical unit that has been employed as the standard or reference (for example, all of Canada). A value of 1.0 would indicate that the region rate is identical to the overall Canadian rate; a value greater than 1.0 would indicate that the rate for that region is higher than the Canadian rate; and, in turn, a ratio value less than 1.0 would indicate that the rate for the specific region is lower than the Canadian rate.
• Significantly different. Computed age-standardized (or sex-standardized, etc.) ratios rarely equal 1.00000, exactly. Questions then arise, for example, "Are the ratio values 0.9 or 1.1 really different from 1.0?" Statistical tests are employed that allow us to state whether a ratio is significantly different at a specified confidence, for example, "I am 95% confident that this ratio is significantly different from 1.0. Its magnitude is not due merely to chance alone".
• Breast Cancer Incidence Maps described in the previous page show age-standardized rates and ratios. Following from the paragraph above, four categories of ratios were mapped and these are listed below. In addition, for each of the ratio mapping categories, the mean or average rate is provided in brackets.

Lower rate (ratio <1.0) that is significantly different from the Canadian rate (73 per 100 000)

Lower rate (ratio <1.0) but not significantly different (88 per 100 000)

Higher rate (ratio >1.0) but not significantly different (102 per 100 000)

Higher rate (ratio >1.0) and significantly different (110 per 100 000)

Income Measures: Methodological Note

(A) Average Income

Average income has been derived from the 1996 Census. These values, computed for census divisions, are based on the total 1995 income reported by individuals 15 years of age and older.

(B) Income Adequacy: Methodological Note

In the 1996 to 1997 National Population Health Survey, income adequacy categories (Table 1) have been defined based on combinations of household income and size of household.

Table 1. Income Adequacy Categories: National Population Health Survey, 1996 to 1997

(C) Low Income Cut-off (LICO) Values (Source: Statistics Canada)

The incidence of low income is the proportion or percentage of economic families or unattached individuals in a given classification below the low income cut-offs. These incidence rates are calculated from unrounded estimates of economic families and unattached individuals 15 years of age and over. Since all members of an economic family share a common status, incidence of low income can also be calculated for the total population in private households.

Measures of low income known as low income cut-offs (LICOs) were first introduced in Canada in 1968 based on 1961 Census income data and 1959 family expenditure patterns. At that time, expenditure patterns indicated that Canadian families spent about 50% of their income on food, shelter and clothing. It was arbitrarily estimated that families spending 70% or more of their income on these basic necessities would be in 'straitened' circumstances. With this assumption, low income cut-off points were set for five different sizes of families.

Subsequent to these initial cut-offs, revised low income cut-offs were established based on national family expenditure data from 1969, 1978, 1986 and 1992. These data indicated that Canadian families spent, on average, 42% in 1969, 38.5% in 1978, 36.2% in 1986 and 34.7% in 1992 of their income on basic necessities. By adding the original difference of 20 percentage points to the basic level of expenditure on necessities, new low income cut-offs were set at income levels differentiated by family size and degree of urbanization. Since then, these cut-offs have been updated yearly by changes in the consumer price index. (refer to Table 2).

Table 2. Low Income Cut-offs for Economic Families and Unattached Individuals, 1995

Additional LICO matrices for the years 1980 to 1998 are provided in the 1999 Statistics Canada publication Low Income Cut-offs (Catalogue 13-551-XIB).