Box whisker shows the secular changes of mean age at menarche for women born between 1930 and 1985. Heavy line, Median; box, 25-75%; whiskers, 95% confidence interval. * There was significant difference between mean age at menarche born in the 1980s and those born in the 1930s, 1940s and 1950s.
Hosokawa et al. BMC Women's Health 2012 12:19 doi:10.1186/1472-6874-12-19