Abstract
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Background
Keywords
Findings
Authors
What is already known on this subject?
What does this study add?
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.
Keywords
Cancer, data collection, incidence, mortality, neoplasms, SEER Program, registries
Findings
Reliable cancer registry data are needed for planning, monitoring, and evaluating cancer control programs. An important aspect of data quality is case ascertainment, generally defi ned as the percentage of all incident tumours in a registry's surveillance population that are captured in the registry's database. Incomplete case ascertainment can lead to underestimated incidence and prevalence, and biased socio-demographic and clinical characteristics (for example, stage at diagnosis, treatment provided, survival) if the cancers recorded by a registry differ substantially from those that are missed. [Full Text]
Authors
Dianne Zakaria (1-613-951-4118; dianne.zakaria@statcan.gc.ca) is with the Health Statistics Division at Statistics Canada, Ottawa, Ontario, K1A 0T6.
What is already known on this subject?
- Incomplete ascertainment of cancer cases by cancer registries can lead to biased estimates, particularly if the missed cases differ substantially from those captured.
- The North American Association of Central Cancer Registries’ (NAACCR) completeness measure expresses the observed number of cancers as a percentage of the expected number, which is calculated using data from registries known to have superb case ascertainment.
- Despite its use, little has been published about the methodology, relative usefulness and accuracy of this measure in Canada.
What does this study add?
- NAACCR’s cancer site-specific completeness of case ascertainment indicator was associated with the basic incidence-to-mortality rate ratio for a region, but not with the percentage of cancers microscopically confirmed or the percentage registered by death certificate only.
- Undercoverage, as identified by the indicator, did not increase consistently with expected case-finding difficulty, but the indicator did identify known undercoverage issues in the Canadian Cancer Registry.
- The importance of examining cancer-specific indicators rather than an overall indicator of case completeness was reinforced, as aggregation of cancer sites with high and low completeness estimates can obscure undercoverage in specific cancers.
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