19. A group of 100 healthy women was followed prospectively for 10 years. All subjects entered the study on January 1, 2000 and all women were followed until December 31, 2009. During this period, 5 subjects were diagnosed with breast cancer. The time at which these 5 subjects developed cancer is shown in the table below (indicated by 'cancer'). Assume that each diagnosis occurred exactly half-way through the respective year, and that two of the subjects were lost to follow-up (indicated by an X in the table), and that these losses to follow-up occurred exactly half-way through the respective year. The other three subjects were not lost to follow-up, and they were still alive at the end of follow-up.

Subject	2000	2001	2002	2003	2004	2005	2006	2007	2008	2009
1				cancer		X
2			cancer
3							cancer
4		cancer			X
5									cancer

a)What was the cumulative incidence of breast cancer over the follow-up period? (2 points)

b)What was the incidence rate of breast cancer over the follow-up period? (2 points)

c) What was the prevalence of breast cancer on August 1, 2006? (2 points)