Collaborative nowcasting of COVID-19 hospitalization incidences in Germany
Fig 2
Illustration of 7-day hospitalization incidences via individual-level timelines.
The reference date by which hospitalizations are counted is the date when the positive test of an ultimately hospitalized person is reported (green dots). However, hospitalizations only become known after they take place (red triangles) and are reported (blue squares). Individuals A-E are included in the 7-day hospitalization incidence of date t because their reference date falls within a 7-day window from t − 6 until t, even though some are reported as hospitalized later (individuals D and E). These hospitalizations only appear in the data with a delay and thus need to be predicted using a nowcasting method on day t. In principle, it is also possible that positive test, hospitalization and reporting all take place on the same day, as for individual C. In this case, there is no delay problem. We note that even though individuals F and G are hospitalized or reported within the period t − 6 to t, they are not counted in the 7-day hospitalization incidence for day t because the positive test is reported before t − 6. Individual H is not included because its reference date is after t.