Objective: The essential assumption of random missing age behind the “conventional method” of handlingcancer patients of unknown age does not often hold. This article is to introduce four alternative methods basedon more acceptable assumptions.
Methods: More cases with unknown age are allocated to the older age-groupsin all the new methods. In the “weighting method,” cases of unknown age are distributed according to distributionof cases of known age, whereas in the “last-group method,” all of them are added to the oldest age-group. In the“progressive method,” unknown-age cases are added to the age-groups above 60 progressively (weighting=1/63,2/63, 4/63, 8/63, 16/63, and 32/63), whereas in the “additive method,” they are allocated to the age-groups above60 additively (weighting=1/21, 2/21, 3/21, 4/21, 5/21, and 6/21). Data were from the Cancer in Five Continentdatabase, vol. VIII.
Results: Age-standardized rates for “All sites” in Zaragoza (Spain), Cali (Colombia), Algiers(Algeria), and Gambia showed that results by all the methods differed, the magnitude ranging from 0.1 to 3.1%depending on the method, registry, sex, and the defined last age-group.
Conclusion: Conventional and weightingmethods are not based on acceptable assumptions. The last-group method is not stable because it depends onthe defined age-group as last (65+, 75+ or 85+). Both progressive and additive methods have more acceptableassumptions. The progressive method is preferable above all others because it can produce an age-specific curvewith the expected exponential increase.