What does “shifted event date” mean?

To ensure participant privacy, some data are subject to suppression (withholding or removing selected information) or generalization based on re-identification risk. Registered Tier data include participant-level data with added transformations, which includes date shifts. All dates in the Registered Tier are shifted backwards by a random number between 1 - 365. The shift is constant for each participant so that temporality of events is preserved. In the Controlled Tier, real (unshifted) dates of events will be available, with the exception of date of birth, which is generalized to year of birth. You can learn more about All of Us privacy methodology here. 

Please review our All of Us Research Program Data Access Framework for further information.