A person may have several doctor-certified and/or self-certified sick leaves during the quarter, which also means that a person may have multiple instances of sick leave. Multiple instances occur when the person works at least one day between sick leave periods. An example of three instances of sick leave during a quarter is a person is on sick leave from 1st to 7th of January, then from 9th to 10th of January, and finally from 12th to 14th of March.