The Statistical Power of Epidemiological Studies Analyzing the Relationship between Exposure to Ionizing Radiation and Cancer, with Special Reference to Childhood Leukemia and Natural Background Radiation

Abstract

Little M.P., Wakeford R., Lubin J.H. and Kendall G.M., The statistical power of epidemiological studies analyzing the relationship between exposure to ionizing radiation and cancer, with special reference to childhood leukemia and natural background radiation. Radiat. Res. The etiology of childhood leukemia remains generally unknown, although risk models based on the Japanese A-bomb survivors imply that the dose accumulated from protracted exposure to low-level natural background ionizing radiation materially raises the risk of leukemia in children. In this paper a novel Monte Carlo score-test methodology is used to assess the statistical power of cohort, ecological and case-control study designs, using the linear low-dose part of the BEIR V model derived from the Japanese data. With 10 (or 20) years of follow-up of childhood leukemias in Great Britain, giving about 4600 (or 9200) cases, under an individual-based cohort design there is 67.9% (or 90.9%) chance of detecting an excess (at 5% significance level, 1-sided test); little difference is made by extreme heterogeneity in risk. For an ecological design these figures reduce to 57.9% (or 83.2%). Case-control studies with five controls per case achieve much of the power of a cohort design, 61.1% (or 86.0%). However, participation bias may seriously affect studies that require individual consent, and area-based studies are subject to severe interpretational problems. For this reason register-based studies, in particular those that make use of predicted doses that avoid the need for interviews, have considerable advantages. We argue that previous studies have been underpowered (all have power <80%), and some are also subject to unquantifiable biases and confounding. Sufficiently large studies should be capable of detecting the predicted risk attributable to natural background radiation.

Impacts of Terrestrial Ionizing Radiation on the Hematopoietic System

“…The hematopoietic system endures energy in mammals and includes bone marrow, which is the main blood-forming system [1][2][3][4][5]. Blood-forming cells are located in bone marrow, and these are highly vulnerable to radiation damage [1, 6-8, 13, 32, 64].…”

Spatial prediction of naturally occurring gamma radiation in Great Britain

“…(Evrard et al, 2006; Richardson et al, 1995; United Kingdom Childhood Cancer Study Investigators, 2002)), most of them reporting a null result. However, the lack of statistical power in these studies (Little et al, 2010) suggests that reliable conclusions cannot be made. A recent and more adequately powered case-control study in Great Britain (GB: England, Scotland and Wales) by Kendall et al .…”

Ionizing radiation and atherosclerosis: Current knowledge and future challenges

“…Finally, Little et al estimated population mortality risks for circulatory disease from exposure to low-level ionizing radiation by extending previous meta-analyses [52] of Japanese atomic-bomb survivors and occupationally exposed groups [53]. Exposures had to involve moderate-or low-dose (cumulative mean < 0.5 Sv) whole-body exposure or exposures at a low dose rate (i.e., <10 mSv/day).…”