Iowa radon vs lung cancer study

[Bernard L Cohen <blc+@pitt.edu>]

COMMENTS ON THE IOWA RADON VS LUNG CANCER STUDY

GENERAL COMMENT
	The principal reason why the Iowa study is claimed to be better
than previous studies is that they did a more elaborate job of estimating
radon exposure doses, by considering exposures outside the home and time
spent in various places inside and outside the home.  I view these
improvements as relatively unimportant because of the other much larger
uncertainties in radon exposures. For one example, they consider only
exposures 5-19 years prior to cancer diagnosis, neglecting earlier
exposures; among the Japanese A-bomb survivors, the majority of lung
cancer deaths occurred more than 20 years after exposure, and according to
the BEIR-VI models, the same should be true of lung cancers induced by
radon. Moreover, the procedures they use to take into consideration the
time spent in various places introduces a whole new set of uncertainties
derived from problems in remembering and reporting habits from 5-19 years
earlier. Are these memories unbiased by more recent times when the cases
were sickly while the controls were healthy? Does the interviewer treat
cases and controls without being biased by the fact that the former are
sick and dying while the latter are healthy? There are also uncertainties
in that radon levels in a particular house may have changed over time. For
example, a crack may have developed (or conversely, have become sealed) in
the basement floor, causing the radon level to be different 15 years ago
than it was in the recent measurement. Similar problems can arise from
changes in ventilation; do window opening habits and use of air
conditioning remain unchanged over 20 years, let alone between hot and
cool Summers?
	For these reasons, I do not accept the claim that this study is
far superior to the others. Uncertainties in radon exposures are important
factors in all of them.

SPECIFIC ISSUES
		The aspect of this study that bothers me most is that the
corrections for time spent in various places makes a very large difference
in the results, greatly enhancing their conclusion that radon exposure is
important, in spite of the fact that the average percentage of time spent
in various places is essentially the same for cases and controls: for
cases vs controls, average percent of time spent in the home is 73.2 vs
72.1, in another building is 14.2 vs 14.4, outside is 7.6 vs 8.5, and away
is 5.0 vs 5.0. While I can understand that mathematically it is possible
that  correcting for where each individual spends her time can make a big 
difference from considering onle the averages, it seems very
difficult to see how the effect can be so systematic as to grossly affect
the results. It seems to me that the authors owe us some explanation to
help us understand such a seemingly improbable situation.
	Another problem that bothers me is that there is no consideration
given to geography, which is a potential confounding factor very closely
correlated with radon levels. Controls are chosen randomly from the entire
state of Iowa, where average radon levels in different counties varies by
a factor of 3, from 1.7 to 5.0 pCi/L. Cases come largely from areas where
there is a high prevalence of smoking, which might easily have different
average radon levels than the controls. It seems important to me that
information be given at least on what counties the cases and controls come
from.
	The cases are nearly all smokers while the controls are nearly all
non-smokers. There are many differences in life styles of smokers and
non-smokers that can affect radon exposures. Some attention should be
given to these. Also there is a substantial difference in educational
attainment between cases and controls which could be a source of trouble.
This is one example of socioeconomic variations which can be important
both in disease vulnerability and in radon exposures, but essentially no
attention is given to socioeconomic factors other than education. The
basis for a case-control study is that cases and controls are matched in
every way except for having contracted the disease. Any deviation from
this would seem to be an issue for concern.
 
Bernard L. Cohen
Physics Dept.
University of Pittsburgh
Pittsburgh, PA 15260
Tel: (412)624-9245
Fax: (412)624-9163
e-mail: blc+@pitt.edu


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