To trial the provision of full information on the benefits and risks of mammography in women that are eligible for breast screening. The knowledge many women have of mammography is not reflective of the recent change in evidence; it is often missing information on over-diagnosis and over-detection. Women tend to overestimate their risk of breast cancer and the benefits of breast screening. In addition, universal breast screening programs are biased towards emphasizing screening. However, a mammogram is not a perfect test and there is no right or wrong decision about whether to have a screening mammogram. It is an individual woman's decision to make. To understand the effect of changing information to reflect the potential for over-diagnosis and over-treatment, we will carry out a pragmatic controlled trial of implementation of balanced information on mammography in family practice.

1:1 double-blinded randomized controlled trial of patients to receive the intervention or standard information (control) at the study start in an information package. The intervention includes a decision aid (previously developed by Hersch et al. 2015, with minor modifications to reflect the Canadian context), a YouTube video link and an invitation to attend a group information session. The intervention or standard information, depending on participants assigned study group, will be mailed or emailed to participants. The information packages will also include questionnaires to collect data on outcome measures. There will be two study waves to account for women's eligibility at different time points (i.e. when approaching a mammogram due date). The first wave of participants will receive their information package at the study start and the second wave of participants will be sent their information packages 6 months after the study start. Each wave of participants will be followed for one year. Data collection will include quantitative measures of factors relevant to the decision-making process. Screening participant rates will be measured for each wave of participants, 6 months and 12 months after their respective enrollment date. Qualitative methods will be used to obtain an understanding of clinician's perception of decision aids in a primary care setting. Outcome measures and analyses will be blinded.

Inclusion Criteria:

• Patient on the active roster of physicians of MUSIC (McMaster University Sentinel and Information Collaboration; McMaster Family Health Team).
• Due for a mammogram (have not had a mammogram ≥ 18 months) according to Canadian screening interval recommendations for routine screening.

Exclusion Criteria:

• Previous history of invasive or non-invasive breast cancer.
• At higher risk for breast cancer compared to the general population i.e. identified as having the BRCA1 or BRCA2 gene, immediate family member has had breast cancer.
• Have had a mammogram within the last 18 months (< 18 months).