The second requirement is a clear and well defined starting point. For popu- lation-based cancer registries, the starting date (from which the survival is calculated) is the incidence date (see Section ). The third requirement is a clear and well defined outcome. Death is gener- ally the outcome of interest, but some registries collect enough data to allow them to conduct analyses using recurrence of tumour, or first recurrence of a particular complication, as the outcome of interest. It is also necessary to formulate clear criteria for deciding who should be considered ‘lost to fol- low-up’. For instance, certain registries would assume that cases for which it was not.
