An examination of the NAACCR method of assessing completeness of case ascertainment using the Canadian Cancer Registry.

BACKGROUND

Despite use of the North American Association of Central Cancer Registries' indicator for assessing completeness of case ascertainment in population-based cancer registries, little has been published about its methodology, usefulness and accuracy in Canada.

DATA AND METHODS

Canadian cancer incidence, cancer mortality, and population census data were used to quantify case completeness in 2007. Two indicators (I₁ and I₂) that expressed the observed age-standardized incidence rate relative to the expected rate were calculated. The assumption of stable age-standardized sex- and cancer-site-specific incidence-to-mortality rate ratios across regions was assessed. Associations between I₁, I₂ and simpler indicators of completeness were examined.

RESULTS

The assumption of stable age-standardized sex- and cancer-site-specific incidence-to-mortality rate ratios across regions was not consistently supported—substantial regional differences emerged. I₁ was strongly correlated with I₂ (r=0.93, n=315, p<0.0001), and both were most strongly and consistently associated with the age-standardized incidence-to-mortality rate ratio. The frequency of undercoverage did not increase consistently with expected case-finding difficulty.

INTERPRETATION

The age-standardized incidence-to-mortality rate ratio may provide a less complicated method of identifying undercoverage.