Journal of Public Health Advance Access originally published online on August 10, 2006
Journal of Public Health 2006 28(3):197-202; doi:10.1093/pubmed/fdl030
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Women’s knowledge about breast cancer risk and their views of the purpose and implications of breast screening—a questionnaire survey
Premila Webster, Senior Lecturer1
Joan Austoker, Director2
1 Department of Public Health, University of Oxford, Institute of Health Sciences, Old Road, Headington, Oxford OX3 7LF, UK
2 Cancer Research UK, Primary Care Education Research Group, University of Oxford, Institute of Health Sciences, Old Road, Headington, Oxford OX3 7LF, UK
Address correspondence to Premila Webster, E-mail: premila.webster{at}dphpc.ox.ac.uk
Objectives To assess women’s knowledge and perception of breast screening, including its benefits and disadvantages, and explore whether demographic and other personal characteristics are associated with accurate knowledge.
Design Questionnaire survey of a random sample of 1000 women aged between 49 and 64 years registered with GPs in Oxfordshire.
Results Thirty-six per cent of women knew the lifetime risk of developing breast cancer, and the interpretation of numeric risks varied among women. There was an association between inaccurate knowledge and lower formal education (P = 0.05). Forty-five per cent of women believed that screening prevents breast cancer. Women were of the opinion that screening helps early detection, could result in less invasive treatment and reassured them. Sixty-three per cent had no concerns about breast screening. The main causes of concern were that they would not be invited for further screening (exclusively women in their 60s), screening is not offered earlier or more frequently, painful mammography and effects of radiation. A minority of women were concerned that the pressure exerted on the breasts during mammography may itself trigger cancer by displacing and spreading cancer cells.
Conclusions Women’s knowledge about breast screening was variable and sometimes incorrect, and those with less formal education were more likely to have inaccurate knowledge.
Keywords: breast cancer screening, informed choice, mammography
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Introduction |
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 TOP Introduction MethodsResultsDiscussionReferences |
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Women invited to attend breast screening are not ill and not all of them will develop breast cancer during the course of their lives. It is therefore vital that these women know the pros and cons of breast screening to help them make an informed choice about attending screening. When a woman chooses to attend mammography, she voluntarily agrees to undergo breast screening. However, this does not imply that she has knowledge and understanding of what is proposed. In order to provide relevant and appropriate information for women invited to attend breast screening, it is important to ascertain women’s current knowledge and understanding of breast screening. This study aims to assess women’s knowledge about mammography screening and gain an understanding of their perception about screening and its benefits and disadvantages.
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Methods |
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Sample size
The sampling frame was women aged 49–64 years registered with GPs in Oxfordshire as they would either have been invited or expect an invitation to attend breast screening in the near future. The sample size that would be sufficient to estimate the proportion of women correctly estimating the lifetime risk of breast cancer (based on the results of an Australian study1) with a 95% confidence interval (CI) and a precision level of 5% was calculated. A random sample of 1000 (8.3%) out of a possible 12 000 women was chosen as the largest sample that was possible to survey with the resources available. This would allow a precision level of 4% with a response rate between 50 and 70%.
Ethics committee approval was obtained for the survey.
Questionnaire design
Where appropriate, pre-validated questions were included in the questionnaire, the face and content validity were assessed and following piloting the questionnaire was posted with the covering letter and information sheet. A reminder was sent out to non-responders after 4 weeks.
Data analysis
Statistical analysis was performed using SPSS 10.0 for Windows.
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Results |
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TOPIntroductionMethodsResultsDiscussionReferences |
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The response rate was 67.5% (n = 640/948) (52 were returned because of wrong address, moved away or death), and in keeping with the population profile of this age group in Oxfordshire,2 the respondents were mainly white home-owning women but from a range of educational backgrounds.
Of the participants who responded to the question, 72% (456/633) had already been invited for screening, 92% attended and 19% were recalled for further tests. Of the respondents, 4% (21/503) had breast cancer, 24% (119/504) had a family history—of these, 45% had a close relative (31% mother and 14% sister).
Knowledge
Lifetime risk
Two questions were included about lifetime risk, one numerical and the other ‘qualitative’.
Of the 608 who responded to this question, 58% (95% CI 54–62%) thought it was ‘inevitable’ or ‘very likely’ that the average woman would develop breast cancer and 42% (95% CI 38–46%) that this was ‘unlikely’ or ‘very unlikely’. When asked about lifetime risk, of the 626 who responded, 36% (95% CI 32–39%) gave the correct response, 12% (95% CI 10–15%) overestimated the risk, 13% (95% CI 10–16%) did not know and the rest underestimated it. Table 1 compares the interpretation of the probability of lifetime risk in the form of words and numbers. It is interesting to note that inevitable/very likely is interpreted over a range of numerical values.
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Associations between numerical lifetime risk knowledge and education, age, screening history (i.e. ever had mammogram, when the last mammogram took place) and personal or family history of breast cancer were examined. Characteristics of those who had a higher proportion of the correct answer included younger women, women with higher formal education, those who had had a mammogram in the last year, were diagnosed with breast cancer or recalled for further tests. However, only educational status was statistically significant (P = 0.05).
A logistic regression model using forward step-wise regression was used to analyse associations between the outcome (accurate numerical knowledge of breast cancer risk) and variables (identified by the previous analysis) that would potentially influence the likelihood of accurate knowledge (Table 2). Educational level was the only predictor of knowledge that was statistically significant. The difference between the unadjusted and adjusted Odds ratio for college-educated respondents was largely because of the influence of family history and diagnosis of breast cancer variables.
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Purpose of screening
Women were asked the purpose of regular breast screening (Table 3). Tests were carried out to explore associations between these variables and educational status, age and lifetime risk knowledge. Women who had answered the lifetime risk question correctly were less likely to respond that screening prevented breast cancer (38% vs. 50% P = 0.006), and women with higher formal education were more likely to respond that screening allows earlier detection of cancer (P = 0.009).
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Recall for further tests
Women were questioned about their knowledge of recall for further tests after breast screening (Table 4). Women who were recalled were more likely to think that recall happens quite often or very often (25%) compared to those who were not recalled (12%) (P = 0.003).
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False negatives
Women were questioned as to how often they thought screening misses cancer (Table 4). Women with less formal education responded that mammography very rarely or rarely misses breast cancer: women with primary/secondary education (45%) versus college-educated women (31%) or graduates or postgraduates (23%) (P 
0.0005).
Interim breast lump
Women were asked what they would do if they found a breast lump within 3 months of a mammogram. The majority, 93% (95% CI 91–95%) (n = 580/623), said they would visit their GP immediately and 6% said they would visit the GP if the problem persisted for more than a month. Of the remaining 1%, two said they would do nothing, one woman said she would wait for the next mammogram and two said they would visit their GP if the problems persisted for more than 3 months and one did not know what to do.
Views about screening
Women’s views about screening were elicited (Table 5). There was no association between these views and age, educational status or accurate knowledge about lifetime risk.
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Views about potential benefits and concerns
Women were asked if they had any views on the potential benefits of regular breast screening. Of the 603 who responded, 26% (95% CI 22–30%) said they had no views. The majority of the views about potential benefits were that screening helps early detection. Other potential benefits stated included (i) less invasive treatment, (ii) reassurance and (iii) women felt they were doing something positive about maintaining good health.
When questioned about any concerns regarding regular breast screening, 63% of the 582 who responded (95% CI 59–67%) said that they had no concerns. Of those who expressed concerns, the commonest were (i) that they would not be invited for further screening (exclusively women in their 60s) (n = 35), (ii) that screening is not offered earlier or more frequently (n = 60), (iii) how painful mammography was (n = 18) and (iv) effects of radiation (n = 25).
A minority of women (n = 5) were concerned that pressure exerted on the breasts during mammography may itself trigger cancer possibly by displacing and spreading cancer cells.
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Discussion |
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TOPIntroductionMethodsResultsDiscussionReferences |
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Women’s knowledge, perceptions and views must be elicited in order to provide appropriate ‘patient centred information’ to enable informed choice in screening.
Main findings of this study
In order to make an informed choice about attending breast screening, women will need to know the lifetime risk of breast cancer to determine the likelihood of developing the disease and put the rest of the information in context. In this study, just over a third knew the lifetime risk which is similar to the results of an Australian study.1 Of the few studies carried out to determine women’s knowledge of lifetime risk of breast cancer, the majority were conducted on those with a family history.3–5 In these studies, over a third of the women had overestimated the risk. In the present study, only 12% overestimated the risk and 39% underestimated it. However, 58% thought it was inevitable or very likely that the average women would develop breast cancer in their lifetime.
The results of the present study indicate that the interpretation of numerical risk varies. This is also borne out in the literature6,7 which suggests that patient’s own risk models bear little relation to the mathematical risk models (i.e. absolute risk, relative risk and numbers needed to treat) used by doctors, and what individuals want is the effect for them as individuals which the doctor’s mathematical model will not tell them. Work done in this area has emphasized that the interpretation of numerical risk information is subject to a wide range of biases.8–10 Ohnishi et al.7 exploring patients’ and physicians’ interpretation of probability found that patients want probability information in the form of words and not numbers.
Although the majority of women (94%) thought that the purpose of screening was early detection, 45% wrongly believed that one of the purposes of screening was to prevent breast cancer.
In order to decide if they want to attend screening, women must be aware that screening is not foolproof and can miss cancers. In this study, in keeping with an Australian study that looked at the public understanding of medical screening,1 32% were not aware of false negatives, and women who held this view were more likely to have less formal education (P 0.0005).
There is evidence to suggest that11 women may undertake screening to be reassured that ‘everything is alright’. Eighty-eight percent of women in this study agreed that screening reassures them. This may result in symptoms being ignored in the future. In addition, false-negative results may create a false sense of security and future symptoms may be ignored. Although the majority of women said they would visit their GP immediately if they noticed a breast lump, a very small minority said they would ignore it.
Studies12,13 carried out in women recalled for further tests following breast screening found evidence that they were significantly less likely to worry about recall if they had received information about the possibility of recall with the initial screening invitation—15% of women in the present study did not know this information.
In keeping with the studies in different countries with differently organized breast screening programmes, women were, in general, positive about breast screening.14–16 Almost all the women who responded to the survey had attended breast screening when they were sent an invitation. A minority of the women expressed concerns about the effects of radiation and pain during mammography. This is reflected in work by other researchers.17,18 An Australian study19 found that providing information about the procedure, the importance of compression and associated discomfort before screening had a significant effect on reducing the levels of discomfort experienced. An interesting finding was the fear women expressed that the compression could itself ‘start’ the cancer. This has the potential to cause unnecessary anxiety, and work needs to be done to explore these beliefs and take measures to allay anxiety.
What is already known on this topic
The majority of researches published assesses information leaflets or gives health professionals views on what information women need to make an informed choice to attend breast screening. Most researchers are of the opinion that the information included with invitations should be more balanced, using absolute numbers to describe the likelihood of benefits and harms.
What this study adds
Our study shows the following:
- Only 36% of women knew the lifetime risk of developing breast cancer and the interpretation of numeric risk varied among women;
- Inaccurate knowledge was associated with lower formal education (P = 0.05);
- Women with lower formal education were also more likely to respond that screening only rarely or very rarely missed breast cancer (P 0.0005);
- Forty-five per cent of women believed that screening prevents breast cancer.
Limitations of this study
The preponderance of white home-owning women makes it difficult to generalize the results to a wider population and to determine if socio-economic conditions or ethnicity has an impact. However, the range of educational backgrounds in the present study was useful to gain some insight into the knowledge and perceptions of women over a range of educational backgrounds.
The study asked only one question about knowledge of numerical epidemiological data on breast screening. There is a point of view20 that this information is essential for women to make an informed choice. It would have been useful to ascertain the understanding of information about risk, false positives and negatives and recall by including numerical statements about risk information. However, experience from other studies in the area suggested that such questions are not completed and lead to too many missing responses.21
It may have been useful to target women recently invited for breast screening to determine their perceptions of screening. However, it was not possible to get the addresses of this sample of women because of data protection.
This study has endeavoured to find out women’s knowledge and perceptions of breast screening as a first step towards providing ‘patient centred information’ to those invited to attend breast screening.
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References |
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- Cockburn J, Redman S, Hill D, et al. Public understanding of medical screening. J Med Screen 1995;2:224–7.[Medline]
- Vital Statistics 2000. Oxfordshire Health Authority.
- Watson M, Duvivier V, Wade-Walsh M et al. Family history of breast cancer: what do women understand and recall about their genetic risk? J Med Genet 1998;35:731–8.
[Abstract/Free Full Text] - Andermann AAJ, Watson EK, Lucassen AM et al. The opinions, expectations and experiences of women with a family history of breast cancer who consult their GP and are referred to secondary care. Community Genet 2001;4:239–43.[CrossRef][Medline]
- Evans DG, Burnell LD, Hopwood P et al. Perception of risk in women with a family history of breast cancer. Br J Cancer 1993;67:612–14.[Web of Science][Medline]
- Misselbrook D, Armstrong D. Thinking about risk. Can doctors and patients talk the same language? Fam Pract 2002;19:1–2.
[Free Full Text] - Ohnishi M, Tsuguya F, Matusi K. Interpretation of and preference for probability expressions among Japanese patients and physicians. Fam Pract 2002;19:7–11.
[Abstract/Free Full Text] - Fischhoff B, Bostrom A, Jacobs Quadrel M. Risk perception and communication. Annu Rev Public Health 1993;14:183–203.[CrossRef][Web of Science][Medline]
- Weinstein ND. What does it mean to understand risk? Evaluating risk comprehension. JNCI Monogr 1999;25:15–20.
- Tversky A, Kahneman D. Judgment under uncertainty; heuristics and biases. In: Kahneman D, Slovic P, Tversky A (eds). Judgment Under Uncertainty: Heuristics and Biases. New York: Cambridge University Press, 1982.
- Milburn K, MacAskill S. Cervical screening: continuing concerns in the 1990s. Health Educ J 1994;53:201–13.
- Wardle J, Pope R. The psychological costs of screening for cancer. J Psychosom Res 1992;36:609–24.[CrossRef][Web of Science][Medline]
- Austoker J, Ong G. Written information needs of women who are recalled for further investigation of breast screening: results of a multicentre study. J Med Screening 1994;1:238–44.[Medline]
- Decker K-M, Harrison M, Tate R-B. Satisfaction of women attending the Manitoba breast screening program. Prev Med 1999;29:22–7.[CrossRef][Web of Science][Medline]
- Roworth MA, McIlwaine GM, Wallace AM. Women’s views of the Scottish Breast Screening Programme: a national consumer opinion survey. Public Health 1993;107:185–92.[CrossRef][Web of Science][Medline]
- Seow A, Straughan P-T, Ng E-H et al. Population-based mammographic screening in Singapore: what are participants’ views? Ann Acad Med Singapore 1998;27:154–60.[Medline]
- Sapir R, Patlas M, Strano S-D et al. Does mammography hurt? J Pain Symptom Manage 2003;25:53–63.[Web of Science][Medline]
- Salazar M-K. Hispanic women’s beliefs about breast cancer and mammography. Cancer Nurs 1996;19:437–46.[CrossRef][Web of Science][Medline]
- Shrestha S, Poulos A. The effect of verbal information on the experience of discomfort in mammography. Radiography 2001;7:271–7.[CrossRef]
- Slaytor EK, Ward JE. How risks of breast cancer and benefits of screening are communicated to women: analysis of 58 pamphlets. BMJ 1998;317/7153:264.
- Anderman A. Patient Education, Risk Communication, and Informed Choice: Women with a Family History of Breast Cancer who Present to Primary Care. DPhil Thesis. University of Oxford, 2002.
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