Subjects considered as eligible due to their age and place of residence are drawn randomly by stratified sampling with unequal probabilities, over-representing individuals with a higher probability of non-volunteering according to age, gender and SES. Random sampling is performed by the Cnav from the French national inter-scheme registry of health insurance beneficiaries (RNIAM), linked to the National careers management system (SNGC).

The Constances cohort constitutes a complex database with characteristics rendering it highly sensitive under the terms of the French data protection act, in particular due to the collection of personal data. Moreover, some data collected at the individual level come from linkage to national databases: National inter-scheme health insurance information system (SNIIRAM), causes of death information system (CépiDc-INSERM) and the Cnav (Annual Social Security declarations, Named quarterly data, absenteeism due to illness, Active solidarity income, maternity). Very strict data collection, organisation, and management constraints are required. The procedures in place conform to legislative and regulatory texts intended to preserve high-level personal data confidentiality and security.

Investigating physicians validate certain identified health events (cancer, cardiovascular or neurodegenerative diseases, etc.). The purpose of these investigations is to collect data or documents (examination or hospitalisation reports, etc.) used to validate the health events and to collect detailed information essential for research.

A biobank, developed through the collection of biological samples in the health clinics, will be associated with the Constances cohort. An in-depth technical analysis was conducted for the creation of a large-scale collection, including several hundred thousand distinct samples, combined with a database of clinical, paraclinical, biological, behavioural and environmental information. The aim is to develop the largest possible collection of biological samples for the future (blood: serum, plasma, urine) and to enable the storage of more specialist samples for specific research purposes.