We used these estimated Pi in this study in several ways. Before January 20, 2020 when the massive intervention was not in position, an estimated Pi > 1 was used as an indication of detecting more than expected cases, while an estimated Pi < 1 as an indication of detecting less than expected cases.
During the early period of massive intervention, an increase trend in Pi over time was used as evidence supporting the effectiveness of the massive intervention in detecting and quarantining more infected cases.
During the period 14 days (latent period) after the massive intervention, Pi < 1 was used as evidence indicating declines in new cases rather than under-detection; thus, it was used as a sign of early declines in the epidemic.