ets exposure, lung cancer - Legacy Tobacco Documents Library

http://legacy.library.ucsf.edu/tid/wyk81f00/pdf
310 I,F.VOIS AND UYAftU
marriagc to a smoker as the b`TS exposure indgx . The resulu of each study were
adjusted for smoking status misclassification-currtat or exsmoketa falsely declaring
themsalves to be never-smokcrs-betorc bcing comhined in th : rnetn•analysis . An
adjustment for background exposure (exposure from soutYxs other than the spouse)
increased the summary rclativc risk to 1 .59 (95% confidencc interval, 1 .02-2.90) . The
relative risk from bttckground ETS exposurc for women married to nonsmokers w-.u
estimsted to be 1 .34 (95% confidencc interval, 1 .01-2 .08) . On the basis of the U .S .
relativc risk estimate of 1 .19 before background adjustment, which was judged to be
statisticafly significant, ond on the basis of the rosults of foreign studies as well as
consideration ofthe biological plausibility of the association, the EPA repon concluded
that there was sufficicnt evidcnce from human studies to ciassify F.'rS as a Group A
(knawn humtin) carcinogen in terms of the EPA Guidelines for Cnrcinogen Risk
Assessment (U .S . EPA, 19$6) .
However, there are problems with the k.PA's risk determination . Its meta-analysis
of U .S . studies omitted two studies which were published before the EPA document
was rcleased ; Brownson et u! . (199' Z) and Stockwcll er ul . (1992) . Using the L'?A's
methods and assumptions, we have calculated a summary relative risk of 1 .07 from
a mera-analysis of 13 U .S . female spousal smoking studies, including these two recent
studies . This relative risk, with 95% conticJence intt :rval of0 .95-1 .21, is not atatistically
significant. Furthermure, iheru is a highly significant (P < 0 .001) inconsistency between
the summary relative risks for six country-specific groups of female spousal smoking
studies considered by the EPA (Table 1) . Thcse relative risks sre all either only wcakly
clevated or, in the atsz of China, below 1,0 . In Section 2 we point out that e likely
explanation for this geographic inconsistency is bias and confounding introduced by
using spousal smoking as an exposurt surrogate . In Section 3 we cxaminc the epidemiologic
data on workplace ETS exposure, which were ignored by the EPA but which
overall exhibit no risk elevation . The inconsistency between the spousul and workplace
studies supports the hypothesis that small risk elevations rcponed in some spousal
studies are due to uncontrolled bias and confounding .
2. BIAS ARISING FROM "I'fiE SPOUSAL SMOKING STUDY DES(GN
Grcc= 2 .01 1 .33 3 .04
Honj Kont 1 .49 1 .16 1 .88
lapan 1 .42 1 .15 1 .75
Western Europc 1,16 0,7E 1 .73
United States 1 .07 0 .95 1 .21
China 0 .34 0 .71 1 .00
Wii ST :ZB--`t66i'TZjSLL :-v6biSjb E) A='MIX01 NI S1N01'T1SNO :)
r
:
non<
evitl :
ine .>r
A
:LtT o:
1 ;10r
nftL
smus
be~ ;,
ciatic
in frL
cou ;
rc c .
ofe :
sn•,c
Stcr
an c!
spou
evar•
clcri~
a~cr
A
thru
tobe
13eca
c : nc
in sG
clas`
was .
et a/
The only explanntion offered by the EPA report for the geographic inconsistency a 2 . :
in the spousal smoking studies was that it could he due to d'tffcrences in the intensity is qt
of spousal exposure between countrics or to diffrrcnces in the ratio of spousal to nte .
0 .89
et a,
TARLE I
misc
MezA•AN&I.YSCS 6(' SKUtsAL St.tORtNG CrtoYMiotAGiC SttJUtES
clmc
fo rr i
Country Rclntivc risk 95% Cnn6dcnco intcrra7 O coul
N ~ relnt A
tion .
~ dosc :
~ ing-
~'°~ rclat