HomeGeneral Q&A

General Q&A

Thank you: The staff at the Million Women Study co-ordinating centre would like to thank all of the women who have taken the time to fill in questionnaires. The response of women across the country has been fantastic, and thanks to these women we are helping find answers to many of the most important and pressing questions about women’s health.

Here are answers to some of the most commonly asked questions about the Million Women Study. The questionnaires page features some useful tips for filling in Million Women Study questionnaires.

What is the Million Women Study investigating? The Million Women Study is investigating how various reproductive and lifestyle factors affect women’s health in the long term. While the initial stimulus for the study was to study risk of breast cancer in women using different types of hormone replacement therapy (HRT), the overall aim was – and remains – to investigate common, largely modifiable, risk for serious and common diseases in women. Our work includes a broad range of risk factors (eg. smoking, diet, alcohol, physical activity, social interaction, genetics) and of health conditions (eg. cancer of many types, heart disease, stroke, dementia, mental health and fracture).

Who is sent a questionnaire? Women were sent the initial Million Women Study recruitment questionnaire with their invitation to attend the National Health Service Breast Screening Programme at participating centres across the country, between 1996 and 2001. Approximately 3 years after completing the first questionnaire, participants were sent a re-survey questionnaire to keep track of their health and to ask new questions about factors such as diet, family history, vitamins and supplements and early life experiences. Re-survey questionnaires have been sent to all surviving women in the study every 3-5 years since then. Some women have also been sent additional postal or online questionnaires.

Why are MY answers important? The Million Women Study aims to provide information which is relevant to all women. To do this as many women as possible, from all walks of life and from all over the UK need to take part. You may think that because you are very healthy/not using hormone replacement therapy/a lifelong non-smoker etc., your answers are not important. In fact, the opposite is true; the only way the study can obtain reliable information about the factors affecting women’s health is to get information from a whole range of different types of women, with different experiences, lifestyles, diets and family histories.

Can I join the study even if I didn’t receive a questionnaire? Recruitment for the study is now finished we are not taking on any new participants. If you are interested in the Million Women Study and would like to know about study results as they emerge, you can go to the study progress section of this web site, which includes up-to-date study findings and publications.

How can I find out what The Million Women Study has found out so far? The Million Women Study web site features the publications produced from The Million Women Study data, newsletters and findings so far. The web site also contains information for those who are taking part in the study, news and event updates and links to other cancer sites. The media and medical journals, some of which are available online, also feature some results and findings from the study.

I need some advice about my health: The Million Women Study cannot advise individual women about hormone replacement therapy, or any other health issues. Anyone with any questions or concerns should contact their general practitioner or other health professional.

I have been asked to give a blood sample what happens next? Please visit the DSW section in our Protocol for further information on this part of the study.

What information does the study hold about me, how is it used and how is it kept secure? Information held includes study questionnaires (postal and email) and data derived from them; linked medical record data for follow-up; blood samples and derived genetic and biochemical data for women in the Disease Susceptibility Study; and records of correspondence with participants. A list of data held by the study can be viewed here.

Data Linkage Linked medical records data are obtained under contract from central NHS record holders (primarily NHS Digital), in England and the Information Services Division in Scotland in Scotland. The Million Women Study provides identifying details such as name, address, date of birth and NHS number for participants, and the provider body uses these to link to their records, and returns linked coded health data to the study. Linked data include Hospital Episode Statistics and Cancer and ONS Mortality data – a full list can be found here.

We use your information in two main ways:
1. Identifying details – name, address, NHS number – are used so we can contact you when necessary, and so that, as you agreed when consenting to take part in the study, we can link to your medical records for follow-up information on your health. A strictly limited number of study staff have access to identifying data.

2. For study analyses, we use pseudonymised datasets containing questionnaire and linked record data. These datasets contain no identifying details. Women are listed only by a study code number- we keep the ‘key’ linking this code number with your identity separately and securely under strictly controlled access. Because we can link back to your identity if we need to, the coded datasets are not irreversibly anonymised and so are referred to as pseudonymised.
Most of the analyses are done by the Million Women Study team. We have a controlled data access policy which means that selected external medical researchers may also use study data, to maximise the benefits of the study. . We share only anonymised or pseudonymised data, under strict regulation.

All study data are held in a secure database in the Cancer Epidemiology Unit at the University of Oxford. The Cancer Epidemiology Unit’s data security processes are approved under the NHS Information Governance Toolkit; our Information Governance and Information Security Policies are available on the Cancer Epidemiology Unit website.

How can I change my contact details? Please telephone us on Freephone 0800 262872 or email us at if you wish to let us know of changes to your name, address or email.

How can I withdraw from the study? You are free to withdraw from the Million Women Study at any time. Please let us know in writing to:

The Million Women Study Co-ordinating Centre
Cancer Epidemiology Unit
Richard Doll Building
Roosevelt Drive
Oxford OX3 7LF
United Kingdom


There are three options if you wish to leave the study, and it is helpful if you can let us know which one you prefer:

No further contact: we will no longer contact you, but you give us permission to keep and continue to use information (and any blood samples) you have already provided, and to continue to obtain and use information from your medical records to follow your health, as before.

No further contact or access to your health records: we will not contact you again and we will not collect any more information through your health records; but you give us permission to keep and use the information (and any samples) already provided.

Complete withdrawal (no further use of data): in addition to no longer contacting you or obtaining information through medical records, we will stop new use of the information and of samples already provided (your information may be included in anonymised datasets already being analysed and it may not be possible to remove your data from these; but we will ensure that your information is not used in future).