Evidence for a secular trend in age of menarche.
D000293:Adolescent; D000367:Age Factors; D000531:Altitude; D004777:Environment; D005060:Europe; D005260:Female; D006128:Growth; D006801:Humans; D008572:Menarche; D005082:Physical Exertion; D013223:Statistics as Topic; D014481:United States