Understanding trends and long-term trends in the incidence of diseases, particularly in cancer, is a major concern of epidemiologists. Several statistical methodologies are available to study cancer incidence rates. Age-Period-Cohort (APC) models may be used to study the variation of incidence rates through time. They analyse age-specific incidence according to three time scales: age at diagnosis (age), date of diagnosis (period) and date of birth (cohort). Classic and Bayesian APC models are available. Understanding geographical variations in health, particularly in small areas, has also become extremely important. Several types of spatial epidemiology studies are available such as disease mapping, usually used in ecological studies. The geographic mapping of diseases is very important in the definition of policies in oncology, namely on the allocation of resources, and on the identification of clusters with high incidence of disease. Geographical association studies, that allow the identification of risk factors associated with the spatial variation of a disease, are also indispensable and deserve special attention in disease incidence studies. For this purpose, Bayesian Hierarchical models are a common choice.

To quantify cancer survival in the absence of other causes of death, relative survival is also considered in cancer population-based studies. Several approaches to estimate regression models for relative survival using the method of maximum likelihood are available.

Finally, having an idea of the future burden of cancer is also of the utmost importance, namely for planning health services. This is why projections of cancer incidence are so important. Several projection models that differ according to cancer incidence trends are available.

The aim of this study is to investigate spatial and temporal trends in the incidence of colorectal cancer, to estimate relative survival and to make projections. It is a retrospective population-based study that considers data on all colorectal cancers registered by the Southern Portuguese Cancer Registry (ROR Sul) between 1998 and 2006.