title: Bias in relative survival methods when using incorrect life-tables: lung and bladder cancer by smoking status and ethnicity in New Zealand.
abstract: Relative survival and excess mortality approaches are commonly used to estimate and compare net survival from cancer. These approaches are based on the assumption that the underlying (non-cancer) mortality rate of cancer patients is the same as that of the general population. This assumption is likely to be violated particularly in the context of smoking-related cancers. The magnitude of this bias has not been estimated. The objective of this article is to estimate the bias in relative survival ratios (RSRs) and excess mortality rate ratios (EMRRs) from using total population compared to correct subpopulation specific life-tables. Analyses were conducted on 1996-2001 linked census-cancer data (including smoking status) for people with lung and bladder cancer, using sex-specific (standard practice), sex- and ethnic-specific, sex- and smoking-specific and sex-, ethnic- and smoking-specific life-tables. Five-year RSRs using sex-specific life-tables, compared to fully stratified life-tables, were underestimated by 10-25% for current smoking and Maori populations. For example, the current smoker male bladder cancer RSR was 0.700 for sex-specific life-tables, compared to 0.838 for fully stratified life-tables. Similarly, EMRRs comparing current to never smokers and Maori to non-Maori were overestimated using sex-specific life-tables only: modestly only for lung cancer, but markedly for bladder cancer. For example, the EMRR comparing current to never smokers with bladder cancer in a fully adjusted regression model was 1.475 when using sex-specific life-tables only, but reduced to 1.098 when using fully stratified life-tables. Substantial bias can occur when estimating relative cancer survival across subpopulations if non-matching life-tables are used.
authors.affiliation: Department of Public Health, University of Otago, Wellington, New Zealand. tony.blakely@otago.ac.nz
authors.forename: Tony
authors.initials: T
authors.lastname: Blakely
authors.forename: Matthew
authors.initials: M
authors.lastname: Soeberg
authors.forename: Kristie
authors.initials: K
authors.lastname: Carter
authors.forename: Roy
authors.initials: R
authors.lastname: Costilla
authors.forename: June
authors.initials: J
authors.lastname: Atkinson
authors.forename: Diana
authors.initials: D
authors.lastname: Sarfati
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015982:Bias; D005260:Female; D006801:Humans; D015993:Life Tables; D008175:Lung Neoplasms / Q000208:ethnology / Q000401:mortality*; D008297:Male; D008875:Middle Aged; D009520:New Zealand / Q000453:epidemiology; D012907:Smoking / Q000009:adverse effects*; D001749:Urinary Bladder Neoplasms / Q000208:ethnology / Q000401:mortality*