Women's perception of mammography screening

J-L Bulliard1 and F Levi1,2

1 Cancer Epidemiology Unit, University Institute of Preventive and Social Medicine, Lausanne, Switzerland. E-mail: jean-luc.bulliard{at}hospvd.ch
2 Vaud Cancer Registry, University Institute of Preventive and Social Medicine, Lausanne, Switzerland

Sirs—In their study on women's perception of the benefits of mammography screening in four countries, Domenighetti and colleagues found an overestimation of the benefits of mammography screening.1 While every effort to tackle the difficult but essential issue of balanced risk information in health prevention is commendable, we have serious concern about two aspects of this study, i.e. its design and conclusions.

Two of the three questions on which the study is based addressed, respectively, the perceived relative (Q2) and absolute (Q3) benefits of regular mammography screening. As the wording of both questions suggests that mammography screening reduces breast cancer mortality and the correct answer is systematically the smallest positive effect among the proposed answers, underestimation of the quantification of the beneficial effect of mammography screening is virtually impossible in this study.2

Further, the restriction to one correct or most appropriate answer for Q2 and Q3 is also questionable. Reporting of the impact of regular mammography screening on breast cancer mortality ranges from none3,4 to about a 50% reduction.5,6 When, as is the case for mammography screening, disseminated messages about the effect are heterogeneous, reflecting in part the diverging opinions held by health professionals on the issue, it is not surprising to observe comparable variations in the perceived quantification of the benefits among the female population. The complexity of Q3 may furthermore require a particularly astute mind, from unprepared respondents, to work out the mathematics behind it (trying this question on work colleagues is informative in this respect).

Question 1, which highlights what screening cannot achieve (primary prevention), with a misleading statement, further emphasizes the crucial importance of wording and selection of answers for closed questions, and the distorting effect that apriorism can have on a study design.2 In the Swiss canton of Vaud where organized screening has been offered to 50–69 year old women for a decade,7 the question ‘What is the purpose of mammography screening?’ was asked in two consecutive random phone surveys of 50–69 year old females, with different allowed answers. One objective was to assess the possible confusion around the term prevention which was believed to be understood by some as ‘prevents the development of a breast cancer toward a fatal outcome’. When ‘to prevent cancer’ was a proposed answer, a majority of respondents opted for this choice with only 43% of females agreeing that mammography screening 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 enables detection of a breast anomaly when ‘to prevent cancer’ was replaced by the probably less confusing ‘to avoid cancer’ (4% of respondents elicited this answer) in the second survey conducted about 4 months later. Adequate quantification of current misconceptions about screening8 is necessary to assess the effectiveness of future strategies aimed at improving public understanding.

Conclusive criticisms of ‘ill informed’ procedures are restricted to breast screening programmes, even though no data on the source of screening information appear to have been collected.1 Sensitization to regular mammography examination generally occurs from several complementary partners, with various incentives to do so. In the Vaud telephone survey, most (59%) women were informed and sensitized about the importance of breast screening by their treating physicians (GPs or gynaecologists) with only 20% reporting the regional screening programme as her source of information. Further, having had a mammography in the last 2 years, whether for screening or diagnostic purpose, is not an appropriate surrogate for participation in organized screening programmes.

While these ‘ill formulated’ questions cannot adequately measure women's perception of the benefits of mammography screening, as might have simpler, open-ended questions, they nevertheless enable two observations to be made: (1) An overwhelming majority of women knew and agreed with a beneficial effect of repeated mammography screening (5% stated that regular mammography screening hardly reduces breast cancer deaths, Q2). (2) The lay public remains confused in appreciating absolute versus relative risks, and these statistics need to be demystified. In our increasingly risk conscious society, valid studies are urgently needed to further elaborate how risk information can be conveyed simply and objectively for improving presentation and content of mammography screening messages,9 so that women could make informed, autonomous choices.

Acknowledgments

This 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 et d'Information Statistiques (SCRIS, Mr Y Ammann) made available the data of the Vaud population surveys.

References

1 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;32:816–21.[Abstract/Free Full Text]

2 Abramson JH. Survey Methods in Community Medicine. 2nd Edn. Edinburgh: Churchill Livingstone, 1979.

3 Gotzsche PC, Olsen O. Is screening for breast cancer with mammography justifiable? Lancet 2000;355:129–34.[CrossRef][ISI][Medline]

4 Olsen O, Gotzsche PC. Cochrane review on screening for breast cancer with mammography. Lancet 2001;358:1340–42.[CrossRef][ISI][Medline]

5 Kerlikowske K, Grady D, Rubin SM et al. Efficacy of screening mammography. A meta-analysis. JAMA 1995;273:149–54.[Abstract]

6 Duffy SW, Tabar L, Chen HH et al. The impact of organized mammography service screening on breast carcinoma mortality in seven Swedish counties. Cancer 2002;95:458–69.[CrossRef][ISI][Medline]

7 Bulliard J-L, De Landtsheer J-P, Levi F. Results from the Swiss mammography screening pilot programme. Eur J Cancer 2003;38:1760–68.[CrossRef][ISI]

8 Thornton H, Edwards A, Baum M. Women need better information about routine mammography. BMJ 2003;327:101–03.[Free Full Text]

9 Paling J. Strategies to help patients understand risks. BMJ 2003;327:745–48.[Free Full Text]





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