Abstract
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Background
Keywords
Findings
Author
What is already known on this subject?
What does this study add?
Background
Relative survival analyses of cancer data often incorporate outdated information about expected survival when current information is not readily available. The assumption is that any bias introduced into the estimation of expected survival, and hence, into the estimate of relative survival, will be negligible. However, empirical studies of potential bias have yet to be published.
Data and methods
Data are from the Canadian Cancer Registry with mortality follow-up through record linkage to the Canadian Vital Statistics Death Database. Period method relative survival ratios (RSRs) for 2005-2007 were derived using life tables centred on the 2006 Census of Population to estimate expected survival. The analysis was repeated using life tables from 5 and 10 years earlier.
Results
Deriving expected survival from life tables 5 years out of date resulted in increases in RSRs for all cancers. These increases became greater with lengthening survival duration. For example, increases in 1-, 5- and 10-year RSRs were 0.2, 0.8 and 1.7 percentage units, respectively, for all cancers combined. Increases in 5-year survival were highest for prostate (2.0) and bladder cancer (1.6); among males (1.2); and among people aged 75 to 99 at diagnosis (1.9). Differences were approximately double when life tables 10 years out of date were used.
Interpretation
The use of historical rather than current expected survival data in calculating RSRs for cancer may lead to consequential overestimation of survival.
Keywords
Bias, epidemiologic methods, life tables, neoplasms, registries, survival
Findings
The relative survival ratio (RSR) is the preferred measure for evaluating and comparing survival in population-based cancer studies. It is defined as the ratio of the observed survival in a group of people diagnosed with cancer to the expected survival of a comparable group of people—free from the cancer under study—in the general population. In practice, expected survival is typically estimated from general population life tables. [Full Text]
Author
Larry F. Ellison (1-613-951-5244; larry.ellison@statcan.gc.ca) is with the Health Statistics Division at Statistics Canada, Ottawa, Ontario, K1A 0T6.
What is already known on this subject?
- Data on expected survival are necessary for the calculation of relative survival and are typically estimated from general population life tables.
- Relative survival analyses often incorporate outdated information on expected survival when current data are not available.
- Empirical studies of the potential bias introduced into relative survival ratios (RSRs) for cancer by using outdated life tables have yet to be published.
What does this study add?
- Deriving expected survival from life tables 5 years out of date resulted in increases in RSRs for all cancers and all survival durations studied.
- Increases were greater as survival duration lengthened.
- Cancers with better prognoses tended to be associated with large increases in RSRs, and vice versa.
- Increases in RSRs were approximately double using life tables that were 10 years out of date.
- The use of outdated expected survival data to calculate RSRs for cancer may lead to consequential overestimation of survival.
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