A medical researcher vaccinated a group of adult patients against human papillomavirus (HPV). He gave each patient two doses of vaccine five months apart. The researcher tested three samples of blood from each of the patients for antibodies against HPV.
Sample 1: taken 3 week before the first dose of vaccine
Sample 2: taken 3 weeks after the first dose of vaccine
Sample 3: taken 3 weeks after the second dose of vaccine
The results are shown in the graph below.
Calculate the percentage increase in the mean concentration of antibodies in the blood between samples 2 and 3.