Academic journal article Canadian Journal of Public Health

An Analysis of the Geographic Variation in Cancer Incidence and Its Determinants in Ontario

Academic journal article Canadian Journal of Public Health

An Analysis of the Geographic Variation in Cancer Incidence and Its Determinants in Ontario

Article excerpt


Cancer incidence data for the Ontario Public Health Units in 1980-91 were examined to investigate regional patterns and the existence of outlier values after adjustment for known risk factors. Candidate risk factors were derived from the Ontario Health Survey and the census. Weighted regressions were fit to the data, and the spatial pattern of the residuals was analyzed.

The number of outlier data points with significant elevations or reductions in risk was close to that expected by chance. They were dispersed geographically, and occurred in a variety of cancer types. We conclude that, in general, most of the geographic variation in cancer risk can be associated with variation in known risk factors, and that there appear to be no broad regional effects remaining after adjustment for these factors. A few cancer sites provide limited evidence of regional effects that may warrant further investigation.


Nous avons revu les donnees statistiques des unites de sante publique de 1'Ontario (1980-91) concernant l'incidence du cancer dans le but d'identifier les determinants potentiels des variations regionales des risques a travers la province. L'information relative aux facteurs de risque provenait de l'Enquete sur la sante de l'Ontario de 1990 et du recensement. Une regression des carres minimises a etc effectuee, ainsi qu'une analyse des correlations spatiales des erreurs.

Le nombre de points extremes rEsultant en one augmentation ou une reduction significative du risque se rapprochait de celui anticipe par l'effet du hazard. Geographiquement, ces extremes etaient distribues a travers la province et etaient observes dans plusieurs types de cancer. Ces donnees demontrent qu'il n'y a pas d'unites oi l'on retrouve un risque de cancer anormalement eleve ou anormalement bas, comparativement a I'ensemble de la province, apres ajustement pour les facteurs de risque connus. Les donnees concernant quelques sites suggerent cependant la possibility d'effets regionaux qui meritent d'etre analyses davantage.

We have previously demonstrated significant spatial patterning in a variety of Ontario cancer incidence rates.' These findings motivated the further analysis, reported here, to investigate if additional regional effects or outlier points could be identified after adjustment for known socioeconomic, lifestyle and environmental risk factors. There are several reasons for carrying out this type of research in Ontario, including: the earlier observations of geographic patterns of cancer risk; the high quality and coverage of the Ontario Cancer Registry (OCR) data; the existence of other data sets on plausible determinants; and the large population base.


The data employed here included: ageand sex-specific cancer incidence rates for various cancer sites, by Public Health Unit (PHU); and selected variables from the Ontario Health Survey (OHS) and the census. Ontario's PHUs are combinations of census divisions (or equivalent), and represent county-level aggregations of municipalities.

Cancer incidence data

The OCR provided the annual number of cases of each of 24 types of cancer by age group (15-19, 20-24,....70-74, and 7584 years), sex and PHU, for 1980-91. The relatively few cases aged <15 or >84 years were excluded to yield comparability with the OHS, as were cases with unknown residence. There were sufficient cases to give a relatively stable estimate of the incidence rate in the majority of the PHUs for most cancer sites. Sex-specific, age-standardized incidence rates were adjusted to the Ontario population using the direct method. Population denominators were obtained from the census.

Ontario Health Survey (OHS) data

The 1990 Ontario Health Survey includes extensive data on social, economic, physical, behavioural, nutritional, occupational and other factors related to health.2 It was completed by 46,228 individuals aged 15-84. …

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