What considerations should I make about dates with survey data?

I’d like to create a combined dataset that looks at survey responses as well as digital health technology data (from Fitbit) according to select data concepts. What considerations should I be aware of before I get started?

Researchers working with Controlled Tier data can join data from all sources by date concepts, including surveys and Fitbit, because dates are consistently included as they are recorded for all data types. Within the Registered Tier, date shifting is applied to all data sources except survey data collected as part of the COVID-19 Participant Experience survey and Minute Surveys on COVID-19 Vaccines series. Because of this, Registered Tier data from the COVID-19 related survey series can not be combined with other data sources by date. The COVID-19 related survey date concepts appear in the Registered Tier exactly as they are recorded, but all other date data has been shifted according to the Registered Tier date shifting rule.