title: Frailty modelling of testicular cancer incidence using Scandinavian data.
abstract: The incidence of testicular cancer is highest among young men, and then decreases sharply with age. This points towards a frailty effect, where some men have a much greater risk of testicular cancer than the majority of the male population. Those with the highest risk get cancer, drain the group of individuals at risk, and leave a healthy male population which has approximately zero risk of testicular cancer. This leads to the observed decrease in incidence. We discuss a frailty model, where the frailty is compound-Poisson-distributed. This allows for a non-susceptible group (of zero frailty). The model is successfully applied to incidence data from the Danish and Norwegian registries. It is indicated that there was a decrease in incidence for males born during World War II in both countries. Bootstrap analysis is used to find the degree of variation in the estimates. In the Armitage-Doll multistage model, the estimated number of transitions needed for a cell to become malignant is close to 3 for non-seminomas and 4 for seminomas in both the Danish and Norwegian data. This paper demonstrates that a model including a frailty effect fits the incidence data well and gives interesting results and interpretations, although this is no proof of the effect's truth.
authors.affiliation: Section of Medical Statistics, University of Oslo, P.O. Box 1122 Blindern, N-0317 Oslo, Norway.
authors.forename: Tron A
authors.initials: TA
authors.lastname: Moger
authors.forename: Odd O
authors.initials: OO
authors.lastname: Aalen
authors.forename: Tarje O
authors.initials: TO
authors.lastname: Halvorsen
authors.forename: Hans H
authors.initials: HH
authors.lastname: Storm
authors.forename: Steinar
authors.initials: S
authors.lastname: Tretli
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D015331:Cohort Studies; D003627:Data Interpretation, Statistical; D003718:Denmark / Q000453:epidemiology; D004812:Epidemiologic Methods; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D009664:Norway / Q000453:epidemiology; D018239:Seminoma / Q000453:epidemiology*; D013736:Testicular Neoplasms / Q000453:epidemiology*