Summarizing indices for comparison of cancer incidence data

Abstract

The desirability of achieving agreement on a method of summarizing cancer incidence is emphasized, and the advantages and disadvantages of the use of the traditional standardized incidence rates are discussed. It is concluded that: No single index is capable of replacing the individual sex‐ and age‐specific incidence rates, and these should always be presented when basic cancer incidence data are published. For aetiological studies age‐specific incidence rates can usefully be summarized in two indices, one (a truncated standardized incidence) showing a standardized incidence over a restricted age range, and the other indicating the rate at which cancer incidence increases with age. An appropriate truncated rate for most epithelial cancers is one for the age range of 35 to 64 years, using weights of 6, 6, 6, 5, 4 and 4 for the individual 5‐year age groups, derived from Segi's (1960) world standard population. For other cancers, age ranges of 0 to 14 years and of 0 to 44 years would be more suitable, with weights of 12, 10 and 9, and 12, 10, 9, 9, 8, 8, 6, 6 and 6 for the corresponding 5‐year age groups. An indication of the general character of a given set of incidence data may be obtained by calculating the ratio of the rates at ages 55 to 64 years and at 35 to 44 years for a combined group of cancers that normally increase rapidly in incidence with age. Further research on practicable ways of indicating the shape of the age‐incidence curve for individual types of cancer is required.