The Markov decision model. The square on the left represents the prophylactic vaccination decision. Each woman's health is tracked by a Markov model after entering the Markov tree (denoted by circles containing an alphabet 'M'). In each cycle, women are at risk of developing oncogenic human papillomavirus (HPV) infection, SIL (squamous intraepithelial lesions), cervical cancer or mortality. The Markov tree branches with ends of rectangles represent the above clinical events that can occur during each 1-year period as a 12-year-old girl is followed until death.