Bulliard, J-L

Levi, F.

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Sirs—In their study on women’s perception of the benefitsof mammography screening in four countries, Domenighettiand colleagues found an overestimation of the benefits ofmammography screening.1 While every effort to tackle thedifficult but essential issue of balanced risk information inhealth prevention is commendable, we have serious concernabout two aspects of this study, i.e. its design and conclusions.Two of the three questions on which the study is basedaddressed, respectively, the perceived relative (Q2) and absolute(Q3) benefits of regular mammography screening. As thewording of both questions suggests that mammographyscreening reduces breast cancer mortality and the correctanswer is systematically the smallest positive effect among theproposed answers, underestimation of the quantification ofthe beneficial effect of mammography screening is virtuallyimpossible in this study.2Further, the restriction to one correct or most appropriateanswer for Q2 and Q3 is also questionable. Reporting of theimpact of regular mammography screening on breast cancermortality ranges from none3,4 to about a 50% reduction.5,6When, as is the case for mammography screening, disseminatedmessages about the effect are heterogeneous, reflecting in partthe diverging opinions held by health professionals on the issue,it is not surprising to observe comparable variations in theperceived quantification of the benefits among the femalepopulation. The complexity of Q3 may furthermore require aparticularly astute mind, from unprepared respondents, to workout the mathematics behind it (trying this question on workcolleagues is informative in this respect).Question 1, which highlights what screening cannot achieve(primary prevention), with a misleading statement, furtheremphasizes the crucial importance of wording and selection ofanswers for closed questions, and the distorting effect thatapriorism can have on a study design.2 In the Swiss canton ofVaud where organized screening has been offered to 50–69 yearold women for a decade,7 the question ‘What is the purpose ofmammography screening?’ was asked in two consecutiverandom phone surveys of 50–69 year old females, with differentallowed answers. One objective was to assess the possibleconfusion around the term prevention which was believed to beunderstood by some as ‘prevents the development of a breastcancer toward a fatal outcome’. When ‘to prevent cancer’ was aproposed answer, a majority of respondents opted for thischoice with only 43% of females agreeing that mammographyscreening enables detection of a lesion and the offer of a less-aggressive treatment (data available on request). However, 93%of respondents adequately stated that screening enablesdetection of a breast anomaly when ‘to prevent cancer’ wasreplaced by the probably less confusing ‘to avoid cancer’ (4% ofrespondents elicited this answer) in the second surveyconducted about 4 months later. Adequate quantification ofcurrent misconceptions about screening8 is necessary to assessthe effectiveness of future strategies aimed at improving publicunderstanding.Conclusive criticisms of ‘ill informed’ procedures arerestricted to breast screening programmes, even though no dataon the source of screening information appear to have beencollected.1 Sensitization to regular mammography examinationgenerally occurs from several complementary partners, withvarious incentives to do so. In the Vaud telephone survey, most(59%) women were informed and sensitized about theimportance of breast screening by their treating physicians (GPsor gynaecologists) with only 20% reporting the regionalscreening programme as her source of information. Further,having had a mammography in the last 2 years, whether forscreening or diagnostic purpose, is not an appropriate surrogatefor participation in organized screening programmes.While these ‘ill formulated’ questions cannot adequatelymeasure women’s perception of the benefits of mammographyscreening, as might have simpler, open-ended questions, theynevertheless enable two observations to be made: (1) Anoverwhelming majority of women knew and agreed with abeneficial effect of repeated mammography screening (5% statedthat regular mammography screening hardly reduces breastcancer deaths, Q2). (2) The lay public remains confused inappreciating absolute versus relative risks, and these statistics needto be demystified. In our increasingly risk conscious society, validstudies are urgently needed to further elaborate how riskinformation can be conveyed simply and objectively for improvingpresentation and content of mammography screening messages,9so that women could make informed, autonomous choices.AcknowledgementsThis work was performed during the tenure (by J-LB)of a Fellowship from the Swiss Science Foundation(Nr. 32–63130.00). The Service Cantonal de Recherche etd’Information Statistiques (SCRIS, Mr Y Ammann) madeavailable the data of the Vaud population surveys.References1 Domenighetti G, D’Avanzo B, Egger M et al. Women’s perception of thebenefits of mammography screening: population-based survey in fourcountries. Int J Epidemiol 2003;32:816–21.2 Abramson JH. Survey Methods in Community Medicine. 2nd Edn.Edinburgh: Churchill Livingstone, 1979.IJE vol.33 no.4 © International Epidemiological Association 2004; all rights reserved. International Journal of Epidemiology 2004;33:903–904Letters to the EditorWomen’s perception of mammography screeningFrom J-L BULLIARD1 and F LEVI1,29031 Cancer Epidemiology Unit, University Institute of Preventive and SocialMedicine, Lausanne, Switzerland. E-mail: jean-luc.bulliard@hospvd.ch2 Vaud Cancer Registry, University Institute of Preventive and SocialMedicine, Lausanne, Switzerland.3 Gotzsche PC, Olsen O. Is screening for breast cancer withmammography justifiable? Lancet 2000;355:129–34.4 Olsen O, Gotzsche PC. Cochrane review on screening for breast cancerwith mammography. Lancet 2001;358:1340–42.5 Kerlikowske K, Grady D, Rubin SM et al. Efficacy of screeningmammography. A meta-analysis. JAMA 1995;273:149–54.6 Duffy SW, Tabar L, Chen HH et al. The impact of organizedmammography service screening on breast carcinoma mortality inseven Swedish counties. Cancer 2002;95:458–69.7 Bulliard J-L, De Landtsheer J-P, Levi F. Results from the Swissmammography screening pilot programme. Eur J Cancer2003;38:1760–68.8 Thornton H, Edwards A, Baum M. Women need better informationabout routine mammography. BMJ 2003;327:101–03.9 Paling J. Strategies to help patients understand risks. BMJ2003;327:745–48.doi:10.1093/ije/dyh227Advance Access publication 26 April 2004904 INTERNATIONAL JOURNAL OF EPIDEMIOLOGYWe thank Bulliard and Levi for their interest in ourinternational population-based survey of women’s perceptionof the benefits of mammography screening.1,2 Our surveyshowed that in the US and three European countries (UK,Italy, Switzerland) a high proportion of women overestimatedthe benefits that can be expected from screeningmammography.Bulliard and Levi argue that the questions used in our surveycould not adequately measure perceptions and that simpler,open-ended questions should have been used. Survey questionscan always be improved, particularly in the light of answersreceived, but we do not think that the use of open-endedquestions would have led to different conclusions. For example,even when classifying the answer that biannual screening inwomen older than 50 years reduces breast cancer mortality ‘byabout half’ as correct, 20% (Switzerland) to 38% (US) ofwomen would overestimate benefits (Table 1 in ref. 2). Thesefindings are in line with the results of a survey in the Canton ofGeneva conducted in 1998.3Bulliard and Levi believe that the wording of the question onwhether screening ‘prevents’ or ‘reduces’ the risk of contractingbreast cancer may have been misunderstood and that usingthe phrase ‘avoids breast cancer’ would have yielded moreappropriate responses. It is clear that the wording of closedquestions can affect responses4 but the change suggested byBulliard and Levi is subtle and unlikely to be of greatimportance. The question was asked in four different languages(English, Italian, German, French) and the frequency withwhich women erroneously chose to answer that ‘regularmammography prevents’ or ‘reduces the risk of breast cancer’was above 50% in all countries. We think that a more plausibleexplanation for these results is the quality of the informationthat is disseminated on mammography screening. For example,an analysis of the contents of leaflets in Australia revealed aworrying emphasis on cancer incidence, despite the fact that theincidence of breast cancer is not reduced by screening.5 Similarresults were recently obtained by Jørgensen and Gøtzsche whoinvestigated relevant websites in Scandinavian and Englishspeaking countries with national breast cancer screeningprogrammes.6Finally, Buillard and Levi disagree with the conclusion thatour results ‘raise doubt on informed consent procedures withinmammography screening programmes’. We agree with Buillardand Levi that women’s perception will be shaped by severalsources of information, and we acknowledge that we didnot ask about these sources. Nevertheless, women withmisconceptions about mammography who participate in breastcancer screening programmes may well have given consent thatis not truly informed. Interestingly, the number of correctanswers among British women aged 50–59 (the women inour study with access to a national screening programme) waslower compared with women from Switzerland and the US,where opportunistic screening dominates. In Switzerland, whenusing the same question in a survey of women aged 50–69living in the Morges district of the Canton of Vaud, where a pilotbreast cancer screening programme has been in place since1995, 80% of respondents believed that that regularmammography reduces or prevents breast cancer7 comparedwith 65% in the national survey.2 These findings may reflectthe dilemma that organized screening programmes face whenattempting both to achieve high coverage and to providebalanced information.8 Indeed, the quality and the extent of the1 Division of Epidemiology and Biostatistics, Department of Social &Preventive Medicine, University of Bern, Bern, Switzerland. E-mail:zwahlen@ispm.unibe.ch2 Laboratory of Epidemiology and Social Psychiatry, Istituto di RicercheFarmacologiche ‘Mario Negri’, Milan, Italy.3 MRC Health Services Research Collaboration, Department of SocialMedicine, University of Bristol, UK.4 Epidemiology Unit, National Cancer Institute Milan, Italy.5 Institute of Social and Preventive Medicine, University of Geneva, Geneva,Switzerland.6 Unit for Research on Patients’ Participation in Health Care, Laboratory ofOncological Clinical Research, Istituto di Ricerche Farmacologiche ‘MarioNegri’, Milan, Italy.7 Cantonal Health Office, Via Orico 5, 6500 Bellinzona, Switzerland andInstitute of Health Economics and Management (IEMS), University ofLausanne, Switzerland.Authors’ responseFrom MARCEL ZWAHLEN,1 BARBARA D’AVANZO,2 MATTHIAS EGGER,1,3 FRANCO BERRINO,4 THOMAS PERNEGER,5PAOLA MOSCONI6 and GIANFRANCO DOMENIGHETTI7

Women's perception of mammography screening

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