Fifty years of cancer incidence: CI5 I-IX.

The Cancer Incidence in Five Continents (CI5) series comprises nine volumes that bring together peer-reviewed results from population-based cancer registries worldwide. The aim of each is to make available comparable data on cancer incidence from as wide a range of geographical locations as possible. In addition, the existence of long time series of data allows the evolution of risk in different populations over time to be studied. The CI5 I-IX database brings together the results from all nine volumes, spanning a period of some 50 years. In addition, unpublished annual data, with more diagnostic detail, are made available for many cancer registries with 15 or more years of recent data. We describe the construction and composition of the CI5 databases, and provide examples of how they can be used to prepare tables and graphs comparing incidence rates between populations. This is the classical role of descriptive statistics: to allow formulation of hypotheses that might explain the observed differences (geographically, over time, in population subgroups) and that can be tested by further study. Such statistics are also essential components in the planning and evaluation of cancer control programmes.