On crude and age-adjusted relative survival rates

Relative survival rates, such as 5- or 10-year relative survival rates, which quantify "net survival" of cancer patients, are the most commonly reported measures of cancer outcome by cancer registries. Because relative survival rates vary with age for many forms of cancer, and because the age distribution of cancer patients varies between different populations or within one population over time, age adjustment of relative survival rates is often employed in international comparisons or in time series analyses of cancer patient survival. In this article, we show that derivation of crude and of age-adjusted relative survival rates in the traditional way is conceptually inconsistent, and that this inconsistency has important practical implications. We show ways to overcome this inconsistency in the derivation and interpretation of crude and age-adjusted relative survival rates.