The data element DaysToEvent is one of two data elements created specifically for the HCUP State Databases that enable users to study multiple hospital encounters for the same patient across hospitals, hospital settings, and time while adhering to strict privacy regulations. The timing information in DaysToEvent must be used in tandem with the data element for the verified encrypted patient linkage number (VisitLink). Before using the revisit variables, please refer to HCUP Supplemental Variables for Revisit Analyses for information on how they are constructed and change over time.

The timing variable (DaysToEvent) is calculated consistently for each verified encrypted patient linkage number (VisitLink) based on a randomly assigned "start date." Each unique value of VisitLink is assigned a unique start date that is used to calculate DaysToEvent for all visits associated with that VisitLink value. The variable DaysToEvent is the difference between the visit's admission date and the start date associated with the VisitLink.

The calculation of days between visits is the difference of DaysToEvent between two selected visits for a verified encrypted patient linkage number (VisitLink). For example, consider a patient with congestive heart failure that has a hospital admission on 1/10/2023 and an ED visit on 1/25/2023. If the DaysToEvent value is "9" for the 1/10/2023 admission and the DaysToEvent value is "24" for the 1/25/2023 ED visit, then the number of days between the two visits is 15 days (24 - 9 = 15). It should be noted that often revisit analyses consider the time between the end of one admission and the start of the next admission. To adjust for the length of the admission, subtract the length of stay from the difference. In the example above, if the first admission had a length of stay of 2 days, then the number of days between the end of the initial inpatient stay and the start of the ED visit is 13 days (24 - 9 - 2 = 13).

The lowest value of DaysToEvent will be on the first or earliest event for a patient. It is important to remember that if patient A has a value of 605 for DaysToEvent and patient B has a value of 300 for DaysToEvent, patient B's event did not necessarily take place prior to patient A's event. In fact, patient B's DaysToEvent value has no relation to patient A's DaysToEvent value. Because of the use of a random start date in the calculation of DaysToEvent, the value of DaysToEvent cannot be compared across patients.

Beginning with the 2009 HCUP data, the revisit variables (VisitLink and DaysToEvent) are included in the Core file of the SID, SASD, and SEDD files, when possible. For 2003-2008 data, the revisit variables are in separate HCUP Supplemental Files for Revisit Analyses.