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:
- The breast screening centres provide information on breast cancer diagnosed through screening in Million Women Study participants.
- Participants are also followed through linkage to medical records, which ensures complete and unbiased follow-up of the whole cohort so that our analyses are reliable. This information is provided to the study through NHS Digital in England and the Information Services Division in Scotland. Details of the linked information held and of data processing and storage can be seen here.
- ‘Update’ follow-up questionnaires are sent to all participants every few years, to find out about changes in factors which may affect health, such as HRT use and smoking, and about health conditions recently diagnosed. So far there have been four update questionnaires, at about 3, 8,12 and 15 years after recruitment, the most recent in 2013/2014.
- Extra questionnaires asking for more detailed information are sent to women who have reported having particular conditions of interest. e.g. breast cancer, and those invited to take part in the Disease Susceptibility Study.