1) The most widely available source for population research is the electoral roll: it contains recent data on age and place of residence for all citizens entitled to vote. But it only includes Certified citizens enrolled, which means it definitely misses illegal migrants, legal migrants who are not citizens, and nationals who have not bothered to enrol.

2) Cancer screening registers: detailed demographic, risk factor and clinical details of women who have used the public sector screening service. Access restricted to health authorities, and some authorised researchers. It does not cover women at high risk who may not use services, and women who attend screening in the private sector (separate registers).

3)Hospital inpatients: as before, but obviously it does not cover healthy or ambulatory ill women.

4)Some hospital hold their own injury or cancer registers, and some health centres hold diabetes registers. Access restricted to hospital staff.

5)Family planning and termination clinics hold computerised socio-demographic and paper-based clinical data only related to the procedures performed in those settings. Usually access restricted to clinic staff.

6) Longitudinal studies: involve the collection of comprehensive data on socio-demographic, risk factor and various health issues. Access to raw data limited to researchers but aggregated data available for planning purposes.

7)Workplaces and other surveys: again, detailed information on limited population sub-group. It misses all self-employed, unemployed, and women in unpaid employment.