The Swiss National Cohort was started in the absence of a unique identifier. Therefore in the beginning combination of deterministic and probabilistic methods was used for linkage, based on sex, date of birth, marital status, nationality, religion, place of residence and other variables.
With the introduction of the yearly repeated Registry Based Census (RBC) in 2010, a unique social security number was included in all databases of the Federal Statistical Office. Though the SNC is not allowed to get the SSN, the cohort receives a unique pseudo ID which is based on the SSN but cannot be traced back to it. This SNC-ID greatly facilitates the linkages of the successive annual RBSc, and their linkage to the mortality, live birth, marriage and divorce registries and annual structural surveys.
For linkage the Canadian probabilistic record linkage software G-Link is used.