Fig. 2
From: IDGenerator: unique identifier generator for epidemiologic or clinical studies
Concept of layered IDs. The study center creates two key files (ID-P, ID-T) and (ID-S, ID-T) before recruitment and transfers a copy of the (ID-P, ID-T) file to a trusted linkage unit. Later in the recruitment phase, the study center may delete the ID-T from the (ID-P, ID-T) key file for already recruited participants and detach the link to the study data. The link may be reconstructed using the original key file from the linkage unit. The study may also choose to exchange the (ID-S, ID-T) list Instead of the (ID-P, ID-T), if the ID-P list requires additional protection and cannot be exchanged