Table 3.

Key temporal anchors in design of a database study ¹

Temporal Anchors	Description
Base anchors (calendar time):
Data Extraction Date ‐ DED	The date when the data were extracted from the dynamic raw transactional data stream
Source Data Range ‐ SDR	The calendar time range of data used for the study. Note that the implemented study may use only a subset of the available data.
First order anchors (event time):
Study Entry Date ‐ SED	The dates when subjects enter the study.
Second order anchors (event time):
Enrollment Window ‐ EW	The time window prior to SED in which an individual was required to be contributing to the data source
Covariate Assessment Window ‐ CW	The time during which all patient covariates are assessed. Baseline covariate assessment should precede cohort entry in order to avoid adjusting for causal intermediates.
Follow‐Up Window ‐ FW	The time following cohort entry during which patients are at risk to develop the outcome due to the exposure.
Exposure Assessment Window ‐ EAW	The time window during which the exposure status is assessed. Exposure is defined at the end of the period. If the occurrence of exposure defines cohort entry, e.g. new initiator, then the exposure assessment may be a point in time rather than a window. If exposure assessment is after cohort entry, follow up must begin after exposure assessment.
Event Date ‐ ED	The date of an event occurrence following cohort entry
Washout for Exposure ‐ WE	The time prior to cohort entry during which there should be no exposure (or comparator).
Washout for Outcome ‐ WO	The time prior to cohort entry during which the outcome of interest should not occur

¹ Anchor dates are key dates; baseline anchors identify the available source data; first order anchor dates define entry to the analytic dataset, and second order anchors are relative to the first order anchor