Wednesday, October 26, 2011

Standardize & Normalize Health Data


Could you please send me the formula that Statistics Canada uses to standardize and normalize its heart attack or diabetes rates per 100,000?


The Health Statistics Division provided the following response and attachments:

Age Standardized Rates (taken from Vital Stats methodology section) Mortality rates, with the exception of crude rates, potential years of life lost (PYLL) and infant and perinatal mortality, as well as cancer incidence and certain CIHI-based data, are age-standardized using the direct method, and the 1991 Canadian Census population structure. The use of a standard population results in more meaningful rate comparisons, as it adjusts for variations in population age distributions over time and across different geographic areas.

Table 5 -  Age standardized rates

Age (in years) Standard population
Less than 1 403,061
1 to 4 1,550,285
5 to 9 1,953,045
10 to 14 1,913,115
15 to 19 1,926,090
20 to 24 2,109,452
25 to 29 2,529,239
30 to 34 2,598,289
35 to 39 2,344,872
40 to 44 2,138,891
45 to 49 1,674,153
50 to 54 1,339,902
55 to 59 1,238,441
60 to 64 1,190,217
65 to 69 1,084,588
70 to 74 834,024
75 to 79 622,221
80 to 84 382,303
85 to 89 192,410
90 and over 95,467
Source: Statistics Canada Cat. No. 84F0208XPB, Causes of Death 1997 The formula for age-standardized death rate r is:

r is equal to the summation over i, for i is between 1 and 20, of w subscript i multiplied by the ratio of d subscript i by p subscript I

Where for age group i,
  is the age-sex specific death count,
  is the population size for a given cause of death and geographical area, and
  is the weight for that group.

Note(s): that the same weight is used for each sex. To yield a rate per 100,000 population, r is multiplied by 100,000.
The confidence intervals for the age-standardized cancer incidence rates were produced using the method found in Estève et al.

For more information on the standardization of rates using the direct method, please refer to the following article found on the Association of Public Health Epidemiologists in Ontario webpage: Standardization of Rates - Namrata Bains

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