The percentage of young women in the 20-24 age bracket who had received the HPV vaccination is estimated from the number of vaccinated women and girls in one-year age brackets at September, 2011. The normal process in the UK is to vaccinate girls when they are 12-13 years old. However, when the process started in 2008 they also decided to vaccinate older girls who were still in school, and the percentage of each school year who were vaccinated was known. Since the so-called ‘catch up’ program had terminated by 2011, we can assume that the rate of vaccination as these girls turned 20 would not have changed significantly. The calculation is therefore based on the age of the young women at each year, increasing as more groups turn 20. Note that since the vaccination groups are based on school years, one-third of the girls turned twenty in a calendar year prior to the remaining two-thirds who would turn 20 in the following year. For example, 2010, was the first year with a significant percentage of 20-24 year olds who had been vaccinated. The percentage of 4.4% is calculated by knowing that 66% of that school year had been vaccinated, but only one-third turned 20 in 2010. Furthermore, 20 year olds only represent 1/5 of the 20-24 monitoring bracket. So, 66% x 1/3 x 1/5 = 4.4%.