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, .,. Publication Bias and Public Health Policy on Environmental Tobacco Smoke Lisa A. Bero, PhD: Stanton A. Glantz. PhD: Drummond Rennie. MD Objective.-To examine the tobacco industry's claim that publication bias against negative studies invalidates the risk assessment of environmental tobacco smoke (ETS) conducted by the US Environmental Protection Agency and other re- views of the health effects of ETS. Design.-Determination of the number of published original research articles that tested the hypothesis that ETS exposure is associated with adverse health ef- fects and that reported statistically significant ("positive") or nonsignificant ("nega- tive") results; the number of articles that concluded that ETS is a health risk; and unpublished studies on the effects of ETS on health. Partlcipants.-Artides identified by a computerized search of the medical literature supplemented with material obtained from the tobacco industry and hand searching. Articles were classified as peer-reviewed journal articles or articles from sponsored symposia. Main Outcome Measure.-The statistical significance of results reported in the article and whether or not the article concluded that ETS exposure is a health risk. flesufts.-More symposium articles than journal articles were reviews (46% vs fi%; P=.0001). More original journal articles than original symposium articles reported the use of statistical tests (96% vs 54%; P=.0001). Of articles with statis- tical analyses, similar proportions of journal articles and symposium articles reported statisticaily significant results (57% vs 47%; P=.329). The conclusions of 80% of the original journal articles were positive, compared with 51 % of the original symposium articles (P=.006). Conclusions.-There is no publication bias against statistically nonsignificant results on ETS in the peer-reviewed literature. The high proportion of articles in symposia that reach the conclusion that ETS is not harmful primarily results from the inclusion of review articles. (J.aMA19942M133-136) PUBLICATION BIAS exists against negative studies: studies that do not present statistically significant results.'-' However, little is known about the ef- fect of publication bias on clinical prac- tice and public health policy. Meta-analy- sis, the combining of numerous small studies into one study for analysis, is a means of answering questions regard- ingthe usefulness of clinical procedures s If negative studies are not published, they might not be included in meta- analyses or widely disseminated .6 In- clusion of unpublished studies in meta- analysis could invalidate or weaken the meta-analysis. One example of how publication bias From the institute for Health Policy Studies (Ors 8ero. Glantz. and Renn e) and Div s on of Cardw+oqy (Dr G)antz). Scnod of fvledcne, and Div s on of C)in cal Pharmacy. Scnoa of Pharmacy (Or Bero), Unrversny of Califom a-San Franc sco. Presented in part at the Second Intemat onal Con- flress on Peer Review in Biomedica! Publicahon, Chi- caQo. I II, SeptemDer 11. 1993. Repnnt reeuests to Institute for Health Policy Stud- es. University of Califomia-San Pranc sco. 1388 Sutter St. 11th F)oor. San Franc sco. CA 94109 (Dr Bero). has been featured in a health policy de- bate has been the tobacco industry's criticism of scientific consensus, docu- ments, and review articles that conclude that exposure to environmental tobacco smoke (ETS) is harmful.''11 For many years some researchers have contended that conclusions regarding the adverse health effects of ETS are invalid be- cause publication bias exists.'2'1i The in- dustry's publication bias argument has been disseminated to the lay commu- nity through tobacco industry press re- leases and the lay press.ta'9 In December 1992, the US Environ- mental Protection Agency (EPA) pub- lished a risk assessment of ETS9 that con- cluded that ETS causes lung cancer in adults and respiratory problems in chil- dren. The risk assessment has significant policy implications, since its approval clas- sified ETS as a known human carcinogen (group A). In June 1993, several tobacco companies filed a lawsuit against the EPA to require the EPA to withdraw both its classification of ETS as a group A car- cinogen and the ETS risk assessment. The tobacco industry's pleading states that "various sources of bias, including publication bias ... could explain any as- sociation claimed by EPA between ETS and lung cancer' ' (emphasis added) and asserts that the EPA "cherry-picked sci- entific data, ignored recent studies that contradicted its conclusions."4 This article tests the validity of the tobacco industry's argument that pub- lication bias invalidates the EPA's risk assessment of ETS and other reviews of the health effects of ETS. Our previous work shows that tobacco industry-spon- sored symposium proceedings are cited by the tobacco industry to support their position that ETS exposure is not harm- ful?t_22 Since symposium proceedings on ETS comprise a substantial proportion of the literature on ETS = we assessed the extent of publication bias among ar- ticles on the effects of ETS on health that had been published as either peer- reviewed journal articles or proceedings of symposia. MATERIALS AND METHODS Published Studies on the Effects of ETS on Heafth Symposium articles (n=297) and a ran- dom sample of peer-reviewed articles (n=100) on ETS were identified as de- scribed previously.-- The MEDLINE, DIALOG, CATALOG, CONFER- ENCE PAPERS INDEX, TOYLINE, and INTERNATIONAL GUIDE TO PERIODICALS databases were searched electronically by using the key words command with "environmental to- bacco smoke," "tobacco smoke pollution," "passive smoking," "involuntary smok- ing," and "symposia," "proceeding," and "conference paper" to identif} 297 sym- posium articles published between Janu- ary 1, 1965, and March 31, 1993. Two symposia were identified from tobacco industry publications and press releases. A MEDLINE search identified 583 non- symposium articles on ETS published in medical or scientific journals between January 1, 1965, and March 31, 1993. Random numbers were generated by computer and used to select 100 articles. Both original research and review ar- ticles were included in the random se- lection. Editorials, articles from con- trolled-circulation journals, and articles JAMA. Juty 13. 1994-Vol 272, No. 2 Pubiicatlort Bias and E1lvirorunenta) Tobacco Srrtoke-8ero et al 133

from supplements were excluded. From the 297 symposium articles and random sample of 100 journal articles, we selected all articles that studied at least one health effect of ETS (eg, epi- demiologic or animal studies on the ef- fect of ETS on lung cancer, pulmonary function, cardiac disease; in vitro stud- ies of ETS carcinogenicity). We identi- fied 114 articles (65 symposium and 49 peer-reviewed articles). We have found previously that sym- posia on ETS contain a larger proportion of review articles (41% reviews) than do the peer-reviewed literature (10% re- views) = Literature reviews provide an opportunity for negative conclusions, whether or not they reflect the conclu- sions of the literature as a whole.m There- fore, we hypothesized that review ar- ticles would contain a larger proportion of negative conclusions than would origi- nal research articl,~s. One of us (L.A.B.) classified each selected article as original or review according to definitions used by the National Library of Medicine. Original articles were those that pre- sented new data or new meta-analyses. Review articles were defined as articles published after examination of published material on a subject that provide an examination of recent or current litera- ture but not extensive critical analyses or statistical syntheses of the literature (Lois Ann Colaianni, written communi- cation, November 26, 1993). Our classi- fication was checked against the elec- tronic coding for articles that were listed in MEDLINE, and agreement was 100~'c. Our first measure of publication bias was to determine the number of articles that reported statistically nonsignificant results. For each article, two reviewers determined independently whether sta- tistical tests were reported for original data or meta-analyses. The quoting of statistical tests from other articles in review articles was not counted. If the results of statistical tests were reported, we classified the article as "positive" if it reported P<.05 (two tailed), confidence intervals excluding 1 for odds ratios, or other statistics that are typically char- acterized as "significant." The articie was classified as "negative" if it reported P>.05 (two tailed), confidence intervals including 1 for odds ratios, etc. If mul- tiple health outcomes were measured and some of the reported statistics were significant and some were not, then the article was classified as showing "mi.ced significance." There was 100,ic agree- ment between reviewers. Our second measure of publication bias was to determine the number of articles that concluded that ETS is not a health risk. We tested the hypothesis that the authors' conclusions regarding the health effects of ETS might not correspond x-ith the statistical results reported. For each article, two reviewers determined inde- pendently w hether the authors' conclu- sion regarding the effects of ETS on health was a "positive conclusion" or a "negative conclusion." One reviewer was masked to the authors. source of the article, and funding of the article. A "posi- tive conclusion" was defined as one that stated that there was an association be- tween ETS exposure and some adverse health outcome. A "negative conclusion" was defined as one that stated that there was no association between ETS expo- sure and any adverse health outcome. Agreement between review ers w as 92~'c, and discrepancies were adjudicated by discussion of the masked article. Identification of Unpublished Studies We attempted to identify studies on the health effects of ETS that have not been published by (1) contacting the US Tobacco Institute (Washingcon, DC), (2) exarnining publications that cited unpub- lished studies, and (3) examining the ci- tations made by tobacco industry-affiIi- ated reviewers in response to the EPA draft risk assessment. This identification process was intentionally biased in favor of the interests of the tobacco industry. The Tobacco Institute publishes sev- eral pamphlets that review the scientific literature on ETS and conclude that ETS is not harmful?l Therefore, we contacted the Tobacco Institute by telephone to see if they could provide for us information on negative studies that have not been published. The Tobacco Institute did not respond to our request for information. We identified publications claiming that negative studies have been excluded from evaluations of the health effects of ETS by searching on the key phrases "publi- cation bias" and "tobacco smoke pollu- tion" in the MEDLINE database and by reading tobacco industry literature on ETS.'2'''-'4-'r' We examined these publica- tions to identifir which unpublished stud- ies, if any, they cited to support the ar- gument regarding publication bias. During preparation of the EPA risk assessment of ETS, the draft was open to technical comment from June 25 to Oc- tober 1, 1990, and was also reviewed by the EPA's Science Advisory Board'° Dur- ing this time, the EPA received 49 com- ments from tobacco industry-affiliated in- dividuals criticizing the conclusions of the risk assessment:=' One argument used by tobacco industry-affiliated reviewers to criticize the draft risk assessment was that negative studies w ere excluded from EPA's risk assessment?' Both the EP A and tobacco industry-affiliated commen- tors cited unpublished studies to support their conclusions regarding the health ef- Tat)1e t-+rumDer ot Onginat ano Review Artiaes on tne r+eartn EHects ot Environmental Tocacco Smoke by Artrcte Classrf,cation• P..r-R.vi.w.o Sympcsium " Artlcl.s Articl.s (n.49) (nw65) Revtew art cies 3 30 Onginat art cles 46 35 •X==2,.7. 01 =1. Po ooo, fects of ETS =` Since the public comment period offered the tobacco industrv the opportunity to produce unpublished stud- ies that did not demonstrate an associa- tion between ETS and health effects, we hypothesized that the tobacco industry- affiliated reviewers would cite unpub- lished negative studies. We counted the number of negative unpublished studies identified by either the EPA or tobacco industrv-affiliated reviewers. Analyses Proportions of statistically significant results and positive and negative con- clusions were compared by means of con- tingency table analysis of symposium vs peer-reviewed articles. RESULTS Published Studies on the Effects of ETS on Health Table 1 shows that srmposium articles on the health effects of ETS were more likely to be reviews than were peer- reviewed articles. None of the review articles described statistical tests used to pool data and derive conclusions. A higher proportion of original. peer-reviewed articles (96`'c [4-1/46]) than original, symposium articles (547c [19/35]) on ETS reported the use of statistical tests (X =30.5. df=1, P<.0001). Table 2 shows that, of the ar- ticles that did report statistical tests. comparable proportions of peer-re- viewed articles and symposium articles reported statistically significant results. Table 3 shows that a larger propor- tion of symposium articles than journal articles had a negative conclusion, ie, they concluded that exposure to ETS is not harmful. When only the conclusions of original studies. regardless of whether they reported statistical results, are con- sidered, the conclusions of 20`<r (9/46) of the peer-reviewed articles were nega- tive. compared with 49<< (17135) of the symposium articles (X==7.67. d1=1, P=.006). The proportion of review ar- ticles in symposia (2 r`%r [SJ'30]) that con- cluded that ETS is a health hazard (a positive conclusion) was lower than the proportion of peer-reviewed review ar- ticles (100% [3/3]) that had a positive conclusion (Fisher's Exact Test, P=.03). 134 JAMA. Ju1y 13. 1992-Vo' 272 No 2 PuDl cat on Bias ano Env ronmental Tooacco Smoke.-3ero et at

t I TaCie 2.-Stausticai S gnrflcance of AruGes on tne Hearm Effects ot Environmentai Tobacco 7y ArnUe Ctassjficat,on' No. (X) . P..r-R.vi.w.d. oriqinai Articf.s WIM Stutfstics (n.44) Symposium. Oriqin.I Artlcles Wtth Statistics (n=t 9) Srgnd cant 25(57) 9(47) Not s gndicant 5(11) 5(26) M«ed s gn thcance 14(32) 5(26) 'x~=2.2. C1=2. P=.329. Table 3-Conclusions of Articles on the Health Effects of Environmental Tobacco Smoke by Article Ctassification• No. (%) P..r•Rovi.wad Symposium Articl.s ArUcl.. Conclusion (n=49) (n-65) Positrve 40(82) 26(40) Negative 9(18) 39(60) d(=t. PS.0001. Identification of Unpublished Studies Of the 11 publications identified that discussed publication bias and the litera- ture on ETS, four cited unpublished studies.t'31"' The remaining publications discussed theoretical reasons for the ex- istence of publication bias but did not cite any unpublished studies.i="'5't'X30 Wood- ward and Mc.'4lichaell conducted the most comprehensive search for unpublished data on ETS because they contacted the tobacco industry and surveyed investi- gators listed in the Directory of Ongoing Research in Cancer Epidemiology regard- ing unpublished studies. They identified one unpublished, negative study of ETS and bladder cancer and one dissertation. We&' cited unpublished data from two studies-the unpublished data on men from the Humble et al-" and Brownson et a131 studies. When Wells added these two unpublished studies to a previously pub- lished analysis, the relative risk of lung cancer increased from 1.5 to 1.7, suggest- ingthat inclusion of the unpublished stud- ies did not invalidate the previous con- clusion that ETS increased the risk of lung cancer. Kilpatrick," in an article pub- lished in a symposium proceeding,l' added one unpublished study to a previously published meta-analysis of ETS and lung cancer and found that the relative risk decreased to less than one. The unpub- lished study identified by Kilpatrick was the same dissertation identified by Wood- ward and Mc-TVlichaeL" Lee presented an unsubstantiated claim that the Ameri- can Cancer Society has never published the results of its large study on ETS and heart disease because the resu,lts are negative. The EPA draft risk assessment con- tained 391 citations," of which three were unpublished studies, two of these being dissertations." Tobacco indus- trv-affiliated reviewers cited 1620 ref- erences.;-! Three references were the same unpublished studies cited by the EPA r-" In addition, tobacco industry- affiliated reviewers cited six additional unpublished studies on the health ef- fects of ETS (T. Sterling, D. Sterling, J. Weinkam, unpublished data)'" Four of the six negative unpublished studies were submitted for publication in peer-reviewed journals'' By the time this article was written, one of these four had been published in a peer-re- viewed journal and one had been pub- lished as a letter to the editor.'6-'' Two of the unpublished studies cited by the tobacco industry-affiliated reviewers were dissertations "•u In summary, we identified five un- published negative studies, two of w hich were dissertations" and none of which was cited among the 501 references in the final draft of the EPA risk assess- ment of ETS ? COMMENT - Our results suggest that there is no publication bias against original research that does not report statistically signifi- cant results on the effects of ETS on health. Almost half of the original re- search published in the peer-reviewed literature reported statistically nonsig- nificant results or results of mixed sig- nificance. The lack of publication bias against negative studies on ETS may not correspond to the occurrence of pub- lication bias as a whole because the great public interest in ETS might favor pub- lication of negative results on ETS. Although similar proportions of both peer-reviewed journal articles and sym- posium articles on the health effects of ETS report statistically significant re- sults, a larger proportion of journal ar- ticles than symposium articles have nega- tive conclusions, ie, conclusions that ETS exposure is not harmful. Although 80% of the journal articles had positive conclu- sions. only 57% of the studies actually reported statistically significant results. This discrepancy is primarily caused by the reporting of results of mixed signifi- cance as being positive. In contrast, the symposia report results of mixed signifi- cance as being negative: When health out- JAMA. July 13, 199a--Vo1 272. No. 2 comes are studied. draw-irtg positive con- clusions from results of mixed significance is justif ed because an intervention (such as ETS exposure) can have adverse health consequences when it affects one physi- ologic measure, even if it does not affect every possible physiologic measure as- sociated w-ith the health outcome. In the symposia. the large proportion of articles with negative conclusions pri- marily results from the inclusion of 22 review articles and 19 original articles that did not report statistical tests. Gen- erating review articles might be one means of publishing negative data on ETS, and such reviews may not be based on a thorough evaluation of the peer- reviewed literature:= In addition, the con- clusions of reviews have been shown to be influenced by the biases of the au- thors'' As none of the review articles identified in this study reported the meth- ods used for pooling data or performing statistical tests, it was impossible to evaluate the selection criteria for articles or the validity of the conclusions. The finding that the symposia contain more review articles and articles without statistical analyses concluding that ETS is not harmful than do peer-reviewed jour- nals supports the supposition that spon- sorship can influence the presentation of results as being positive or negative. We found previously that six of 11 symposia on ETS were sponsored by the tobacco industry.= Anassoaation has been dem- onstrated between pharmaceutical-indus- try sponsorship for research and positive conclusions that support the use of new therapies.' Publication bias has been de- fined as a "systematic tendency to pub- lish any one type of result, be it positive, negative, or null."60 In the ETS symposia, there appears to be a bias toward the publication of negative conclusions that are not supported by the available data. It is hypothetically possible that sta- tistically nonsignificant studies on ETS have been submitted to peer-reviewed journals, rejected for publication, and remain unpublished. However, exhaus- tive searches for unpublished data by ourselves and others have produced only a few dissertations and articles. Al- though industries strive to keep their data proprietary,st they should make available negative data if they are going to claim that publication bias invalidates conclusions based on the medical litera- ture. The failure of researchers with negative findings to submit their papers to peer-reviewed journals has been shown ~= It has also been argued that relying on statistical cutoffs, such as P<.05 or 95% confidence intervals, is inappropriate and discourages authors from submitting nonsignificant re- sults.5'S' There is, however, no evidence Publication Bias and Environmental Tobacco Srno+ce-8ero et a( 135

that these issues have prevented put•- lication of negative studies on ETS. The tobacco industry has used the poe- sibility of publication bias to argue that reviews of the literature on the health effects of ETS are invalid.'7,t"2",y4&56 In the case of Flue-Cured Tobacco Co- operative Stabilization Carp v EPA. the tobacco industry claims that publication bias invalidates the EPA risk assessment because negative studies have been ex- cluded."' Our findings suggest that nega- tive studies, such as those published in s,vmposia, should be carefully scrutinized before they are included in reviews or considered by the courts because the negative conclusions may not be sup- ported by any statistical analyses. The R.fsrsnc.s 1. Sterling TD. Publication dedsions and their pos- sible effects on inferences drawn from tests of sig- nificance-or vice versa. J Am Stat Assoc. 1959; 54:30-34. 2. Dickerain K The existence of publication bias and risk factors for its occurrence. JAMA. 1990; 263:1385-1389. S. Easterbrook PJ, Berlin J, Copalan R. Matthews DR. Publication bias in clinical research. Lancet• 1991;337:86 i-872- 4. Rennie D. Flanagin A. Publication bias: the tri- tunph of hope over experience. JAMA. 1992:.°67: 411412. 5. L'A bbe KA. Detsky AS. O'Rourke K. Meta-analy- sis in clinical research. Ann Intern Med. 1987;107: 224-233. 6. Cook DJ• Guyatt GH. Ryan G• et aL Should unpublished dat3 be included in meta-analyses? cur- rent comictions and controversies. JAMA 1993; 2692749-2753. 7. The Health Consequences oflnvoluntary Smok- ing: A Report of the Surgeon General. Washington, DC: US Dept of Health and Human Services; 1986: 332. DHHS publication CDC 87-8398. 8. National Research Council. Environmental To- bacco Smoke: Meaauring Ezposures and Assess- ing Health Effects. Washington. DC: *Iational Acad- emy Press; 1986. 9. Respirarory Health Effects of Pasaive Smoking: Lung Cancer and Other Disorde•rs. Washington, DC: Indoor Air Division. Office of Atmospheric and Indoor Air Programs. Office of Air and Radiation, US Environmental Protection Agency- 1992. 10. Glantz SA. Parmley WW. Passive smoking and heat2 disease: epidemiology, physiology and bio- chemistry. Cirrulatura. 1991:83:1-12. 11. Steenland K. Passive smoking and risk of heart disease. JAMA 1992267:94-99- 12. Vandenbroucke JP. Passive smoking and lung csncer- a publication bias? BMJ. 1988296:391392. 13. Mantel N. The passive smoidng myth. In: Bieva CJ, Courtois Y. Govaerts M, eda. The Present and Future of Indoor Air Quality. Amsterdam, the .Netherlands: Excerpts Medics; 1989:155-159. 14. KilpatrickSJ.Theepidemiologyofenvironmen- ul tobattro smoke (ETS) and the weight ofevidence argument. Int Surg. 1992:771:131-133. I5. Sugita M. Kanamori M, Izuno T. Miyakawa M. Estimating a summarized odds ratio whilst elimi- nating publication bias in meta-anatysis. Jpn J Clin f?nco l. 1992:=-354358. 16. Armitage AK. Environmental tobacco smoke and coronary heart disease. J Smoking Rel Disord 1993:4•_7-36. 17. Caldwell ADS. Give a dog-end a bad name. .1 Smoking Rel Diaord. 1992;4:1 -1 18. Science Does Not Support Draft Documents L'ndtrgotng Erpert Review. Washingtan. DC: To- bacco Institute: 1990. recent US Supreme Court decision in Daubert v Merrell Dow Pharmacetcticala Inc regarding the standards that govern the admissibility of scientific evidence at a trial suggests guidelines regarding the consideration of data for public health policies (New York Tim.es. June 30,1993: AS) a' The court ruled that federal judges must ensure that scientific evidence and testimony admitted in trials are "not only relevant, but reliable." Judges were urged to consider'~vhether the theory in ques- tion can be (and has been) tested, whether it has been subjected to peer review and publication, its known or potential error rate, and the e)istence and standards con- trolling its operation, and whether it has attracted widespread acceptance Within 19. Huber GL. 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DC: Indoor Air Di- vision, Office of Atmospheric and Indoor Air Pro- grams, Office of Air and Radiation, US Environ- mental Protection Agency; 1990. 35. Humble CG, Samet JM. Pathak DR• Marriage to a smoker and lung cancer risk. Am J Public Health. 1987: '~ 0986()2. 36. Brownson RC. Reif JS• Keefe TJ, Ferguson SW, Pritzl JA. Risk factors for adenocarcinoma of the lung. Am J Epidrntioi. 1987;1252534. 37' 4arela L. Assessment of the r1Asocsatura Be- tween Passive Smokinq and Lung Cancer. New Haven• Conn: Yale Univetsity: 1987. Dissertation. 3& Svensson C, Perahagen G, Klominek J. Smok- a relevant scientific community-."' For negative unpublished data, we recom- mend that the courts, as well as all sci- entists, asse~ whether the data have been submitted for publication in a peer-re- viewed journal, whether the article pre- sents original research, whether the ar- ticle actually reports statistical tests, the quality of the methods, and the source of funding for the research. This study was supported by funds provided by the Cigarette and Tobacco Surtsx Fund of the Sute of California through the Tobacco-Related Disease Research Program of the University of California under awards 2KT0072 (Dr Bero) and 1RT52D (Dr Glantz). We thank Mildred Cho, PhD• for comments and Phillip Lollir for administrative help. inp and Patrive Smoking in Relation to Lung Can- cer in Womert. Stockholm. Sweden: Dept of Epi- demiology, National Institute of Emvronmental Hedidne; 1988. 39. Lsrn WIi. A Clinical and Ep dEmuilogical Study of Carrinoma of Lung in Hong Kong. Hong Kong: University of Hong Kong; 1985• Dissertation. 40. SterlingT, Sterling D, WeinkamJ. Comparison of risk of chronic conditions and cancer between homemakers and otherwise unemployed women. Submitted for publication. 41. SteriingTD,RoeenbaumWL,WeinkamJJ.Bins in the diagnosis of lung cancer and its possible consequences in establishing smoking related risks. Submitted for publication. 42 Feuer G, Ecobichon DJ. 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Publ cauon Bias and Enwronmentai Tobacco Smo+ce-Bero et ai 136 JAMA, Juty 13. 199_?-VOt 272. No. 2