6. A cohort study is performed to evaluate an outbreak of COVID-19 in a jail. The data are presented below. The table shows the events for all persons who experienced an event amongst a cohort of 150 persons. The outcome is COVD-19. The circles represent the onset of COVID-19. The dashed line indicates the duration of COVID-19. X indicates that the COVID-19 was resolved at the end of that day. W indicates withdrawal from the study. D indicates death. Week 1 Week 2 Week 3 Person M W Th F Sa Su. M T W Th F Sa Su. M T W Th F Sa Su days 0 -- 12 -x W D W O - - W -X 11 -X D 15 D a. (5 points) Fill in the number of person-days for each person who experienced an event. What is the total number of person days all participants contributed to the study? b. (5 points) What is the prevalence of COVID-19 on Friday of the second week of the study? Interpret this measure in a sentence. c. (5 points) What is the cumulative incidence (risk) of COVID-19 over the three-week period? Interpret this measure in a sentence. d. (5 points) What is the incidence rate of COVID-19 during the study period? Interpret this measure in a sentence