Cohen's Ecologic Studies

[epirad@mchsi.com]

FYI 



Radiol. Prot. 22 (June 2002) 141-148



The potential for bias in Cohen's ecological analysis of 

lung cancer and residential radon

Jay H Lubin



Biostatistics Branch, Division of Cancer Epidemiology 

and Genetics, National Cancer Institute, EPS/8042, 6120 

Executive Blvd, Rockville, MD 20892-7244, USA



E-mail: lubinj@mail.nih.gov



Received 7 November 2001, in final form 28 January 2002, 

accepted for publication 5 March 2002

Published 30 May 2002 



Abstract. Cohen's ecological analysis of US lung cancer 

mortality rates and mean county radon concentration 

shows decreasing mortality rates with increasing radon 

concentration (Cohen 1995 Health Phys. 68 157-74). The 

results prompted his rejection of the linear-no-

threshold (LNT) model for radon and lung cancer. 

Although several authors have demonstrated that risk 

patterns in ecological analyses provide no inferential 

value for assessment of risk to individuals, Cohen 

advances two arguments in a recent response to Darby and 

Doll (2000 J. Radiol. Prot. 20 221-2) who suggest 

Cohen's results are and will always be burdened by the 

ecological fallacy. Cohen asserts that the ecological 

fallacy does not apply when testing the LNT model, for 

which average exposure determines average risk, and that 

the influence of confounding factors is obviated by the 

use of large numbers of stratification variables. These 

assertions are erroneous. Average dose determines 

average risk only for models which are linear in all 

covariates, in which case ecological analyses are valid. 

However, lung cancer risk and radon exposure, while 

linear in the relative risk, are not linearly related to 

the scale of absolute risk, and thus Cohen's rejection 

of the LNT model is based on a false premise of 

linearity. In addition, it is demonstrated that the 

deleterious association for radon and lung cancer 

observed in residential and miner studies is consistent 

with negative trends from ecological studies, of the 

type described by Cohen.

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