Problem of small numbers in reporting of cancer incidence and mortality rates in Indian cancer registries.

The present paper examines the problem of small numbers (<20 cases) associated with many sites of cancers in Indian cancer registries. The cancer incidence data of 14 Population Based Cancer Registries for the periods of 2001-03 and 2004-05 were utilized for the analysis. Nine out of 14 registries had more than 50% of their sites being associated with small numbers while seven registries had 50% of their sites having as low as 5 cases. Sites associated with small numbers showed a lot of variation and significant differences in their incidence rates within two years duration which are not feasible. The percentage age distribution was also found to vary with different periods. The paper has effectively shown the effect of population size on incidence rates. For a registry of population size 300,000, the incidence rate of 6 can very well be unstable. There are many registries in the world with their population size less than 200,000. Even in the case of registries with high population (>or= 500,000) the practice is to report the cancer incidence by different ethnic groups with populations less than 200,000 and thereby introduce the problem of small numbers in reporting the incidences of various cancer sites. To overcome this problem, pooling of data over broad age groups or ten years age groups or 3 to 5 years periods is one immediate solution.