Cancer Incidence Rates and the Problem of Denominators - a New Approach in Indian Cancer Registries

In India, the national census provides population figures once every 10 years. However, since cancer incidencedata provide various rates for five year age groups, the calculation of the relevant population estimates for agiven year between any two-census years, serving as denominators, assumes importance. The IndividualExponential Growth Rate Method is in current use by various Indian cancer registries to estimate the populationby five yearly age groups. Using the five yearly age group estimates by the same method, various rates like theCrude rate, Age Standardized Rate and Cumulative Rates, are reported in Cancer Incidence in Five Continents,Vol. VIII. However, this approach has been shown to suffer from bias and often results in sacrificing the overallgrowth rate and corrections become necessary in five yearly age group populations to maintain it. We hereshow that the proposed Difference Distribution Method is able to maintain the overall growth rate and overcomesthe bias in estimation of different five yearly age group populations. Further, for population projections, thismethod scores over the Individual Exponential Growth Method, serving as a new methodology for populationestimation by five yearly age groups for inter-census years for Indian cancer registries.