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How information about overdetection changes breast cancer screening decisions: a mediation analysis within a randomised controlled trial
  1. Jolyn Hersch1,2,3,
  2. Kevin McGeechan1,2,3,
  3. Alexandra Barratt1,2,3,
  4. Jesse Jansen1,2,3,
  5. Les Irwig1,2,
  6. Gemma Jacklyn1,2,
  7. Nehmat Houssami1,2,
  8. Haryana Dhillon3,4,
  9. Kirsten McCaffery1,2,3
  1. 1 School of Public Health, The University of Sydney, Sydney, New South Wales, Australia
  2. 2 Wiser Healthcare, The University of Sydney, Sydney, New South Wales, Australia
  3. 3 Centre for Medical Psychology and Evidence-based Decision-making (CeMPED), The University of Sydney, Sydney, New South Wales, Australia
  4. 4 Central Clinical School, The University of Sydney, Sydney, New South Wales, Australia
  1. Correspondence to Dr Jolyn Hersch; jolyn.hersch{at}


Objectives In a randomised controlled trial, we found that informing women about overdetection changed their breast screening decisions. We now present a mediation analysis exploring the psychological pathways through which study participants who received the intervention processed information about overdetection and how this influenced their decision-making. We examined a series of potential mediators in the causal chain between exposure to overdetection information and women’s subsequently reported breast screening intentions.

Design Serial multiple mediation analysis within a randomised controlled trial.

Setting New South Wales, Australia.

Participants 811 women aged 48–50 years with no personal history of breast cancer.

Interventions Two versions of a decision aid giving women information about breast cancer deaths averted and false positives from mammography screening, either with (intervention) or without (control) information on overdetection.

Main outcome Intentions to undergo breast cancer screening in the next 2–3 years.

Mediators Knowledge about overdetection, worry about breast cancer, attitudes towards breast screening and anticipated regret.

Results The effect of information about overdetection on women’s breast screening intentions was mediated through multiple cognitive and affective processes. In particular, the information led to substantial improvements in women’s understanding of overdetection, and it influenced—both directly and indirectly via its effect on knowledge—their attitudes towards having screening. Mediation analysis showed that the mechanisms involving knowledge and attitudes were particularly important in determining women’s intentions about screening participation.

Conclusions Even in this emotive context, new information influenced women’s decision-making by changing their understanding of possible consequences of screening and their attitudes towards undergoing it. These findings emphasise the need to provide good-quality information on screening outcomes and to communicate this information effectively, so that women can make well-informed decisions.

Trial registration number This study was prospectively registered with the Australian New Zealand Clinical Trials Registry (ACTRN12613001035718) on 17 September 2013.

  • breast imaging
  • overdiagnosis
  • decision aid
  • informed decision making
  • cancer screening
  • mediation

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  • Twitter @jolynhersch @wiserhealthcare

  • Contributors All authors contributed to study design. KMC, AB, JJ, NH, HD and KMG obtained funding. JH, KMC and JJ led development of the intervention and implementation of the trial. KMG advised on the statistical analysis. JH performed the statistical analysis, produced the tables and figure and drafted the manuscript. All authors contributed to data interpretation and critically reviewed the manuscript.

  • Funding This work was supported by the National Health and Medical Research Council of Australia through project grant number 1062389.

  • Competing interests None declared.

  • Ethics approval This study was approved by the University of Sydney Human Research Ethics Committee (2012/1429). Participants gave informed consent to take part in the study.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data sharing statement The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

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