The methods of the Million Women Study and the characteristics of the first 121,000 women recruited into the study have been described in detail in a published paper. See our Publications page for more information.

Study design: The Million Women Study is a multi-centre, population-based prospective cohort study of women aged 50 and over invited to routine breast cancer screening in the UK.

Population: All UK women aged 50-64 who are registered with a general practitioner are invited to attend routine mammographic screening for breast cancer, approximately once every three years, at one of about 100 NHS screening centres nationwide. Sixty-six of these centres are collaborating in the Million Women Study.

Recruitment: Women were recruited into the study between 1996 and 2001. At participating centres women received a Million Women Study questionnaire accompanying their invitation to screening, and were asked to return the completed questionnaire at the screening appointment. The questionnaire requested information on past medical history, lifestyle and reproductive factors as well as details regarding oral contraceptive and hormone replacement therapy use. Each woman was also asked for identifying information and written permission for follow-up.

The cohort: Women who participate in the Million Women Study are members of the general public, with a very broad range of backgrounds, health experiences and lifestyles. This range of experiences means that, in the future, it will be possible to investigate whether or not exposure to a particular factor is related to the risk of developing certain diseases. For example, the health outcomes of women who have used hormone replacement therapy can be compared with those who have not used it. Women participating in the Million Women Study were not asked to change their lifestyles in any way; they were only asked to provide information about their health, lifestyle and experience at the time of filling in the questionnaire.

Follow-up: Women who completed the recruitment questionnaire, provided signed consent and supplied information for follow-up are monitored for future health events in a number of ways: