1 Division of Epidemiology and Biostatistics, Department of Social & Preventive Medicine, University of Bern, Bern, Switzerland. E-mail: zwahlen{at}ispm.unibe.ch
2 Laboratory of Epidemiology and Social Psychiatry, Istituto di Ricerche Farmacologiche Mario Negri, Milan, Italy
3 MRC Health Services Research Collaboration, Department of Social Medicine, 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 of Oncological Clinical Research, Istituto di Ricerche Farmacologiche Mario Negri, Milan, Italy
7 Cantonal Health Office, Via Orico 5, 6500 Bellinzona, Switzerland and Institute of Health Economics and Management (IEMS), University of Lausanne, Switzerland
We thank Bulliard and Levi for their interest in our international population-based survey of women's perception of the benefits of mammography screening.1,2 Our survey showed that in the US and three European countries (UK, Italy, Switzerland) a high proportion of women overestimated the benefits that can be expected from screening mammography.
Bulliard and Levi argue that the questions used in our survey could not adequately measure perceptions and that simpler, open-ended questions should have been used. Survey questions can always be improved, particularly in the light of answers received, but we do not think that the use of open-ended questions would have led to different conclusions. For example, even when classifying the answer that biannual screening in women older than 50 years reduces breast cancer mortality by about half as correct, 20% (Switzerland) to 38% (US) of women would overestimate benefits (Table 1 in ref. 2). These findings are in line with the results of a survey in the Canton of Geneva conducted in 1998.3
Bulliard and Levi believe that the wording of the question on whether screening prevents or reduces the risk of contracting breast cancer may have been misunderstood and that using the phrase avoids breast cancer would have yielded more appropriate responses. It is clear that the wording of closed questions can affect responses4 but the change suggested by Bulliard and Levi is subtle and unlikely to be of great importance. The question was asked in four different languages (English, Italian, German, French) and the frequency with which women erroneously chose to answer that regular mammography prevents or reduces the risk of breast cancer was above 50% in all countries. We think that a more plausible explanation for these results is the quality of the information that is disseminated on mammography screening. For example, an analysis of the contents of leaflets in Australia revealed a worrying emphasis on cancer incidence, despite the fact that the incidence of breast cancer is not reduced by screening.5 Similar results were recently obtained by Jørgensen and Gøtzsche who investigated relevant websites in Scandinavian and English speaking countries with national breast cancer screening programmes.6
Finally, Buillard and Levi disagree with the conclusion that our results raise doubt on informed consent procedures within mammography screening programmes. We agree with Buillard and Levi that women's perception will be shaped by several sources of information, and we acknowledge that we did not ask about these sources. Nevertheless, women with misconceptions about mammography who participate in breast cancer screening programmes may well have given consent that is not truly informed. Interestingly, the number of correct answers among British women aged 5059 (the women in our study with access to a national screening programme) was lower compared with women from Switzerland and the US, where opportunistic screening dominates. In Switzerland, when using the same question in a survey of women aged 5069 living in the Morges district of the Canton of Vaud, where a pilot breast cancer screening programme has been in place since 1995, 80% of respondents believed that that regular mammography reduces or prevents breast cancer7 compared with 65% in the national survey.2 These findings may reflect the dilemma that organized screening programmes face when attempting both to achieve high coverage and to provide balanced information.8 Indeed, the quality and the extent of the information provided about both the possible benefits and adverse events of a screening test may dramatically change the willingness of people to participate.9 We therefore maintain that the female populations studied in our survey in four countries appear to be poorly informed about the likely benefit of mammography screening and that many women offered screening may not be able to exercise informed choice.
References
1 Bulliard JL, Levi F. Re: Women's perception of the benefits of mammography screening: Population based survey in four countries. Int J Epidemiol 2004;33:DOI:10.1093/ije/dyh227.
2 Domenighetti G, D'Avanzo B, Egger M et al. Women's perception of the benefits of mammography screening: Population based survey in four countries. Int J Epidemiol 2003;32:81621.
3 Chamot E, Perneger TV. Misconceptions about efficacy of mammography screening: a public health dilemma. J Epidemiol Community Health 2001;55:799803.
4 Aday LA. Formulating questions about knowledge and attitudes. In: Aday LA. Designing and Conducting Health Surveys. San Francisco: Jossey-Bass Publishers, 1991, pp. 17586.
5 Slaytor EK, Ward JE. How risks of breast cancer and benefits of screening are communicated to women: analysis of 58 pamphlets. BMJ 1998;317:26364.
6 Jorgensen KJ, Gotzsche PC. Presentation on websites of possible benefits and harms from screening for breast cancer: cross sectional study. BMJ 2004;328:14854.[CrossRef][ISI][Medline]
7 Domenighetti G. Informed choice in screening. Position paper prepared for the British National Health Service, 2000.
8 Raffle AE. Information about screeningis it to achieve high uptake or to ensure informed choice? Health Expect 2001; 4:9298.[CrossRef][Medline]
9 Domenighetti G, Grilli R, Maggi JR. Does provision of an evidence-based information change public willingness to accept screening tests? Health Expect 2000;3:14550.[CrossRef][Medline]
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