G. Stanley Hall is generally credited by psychologists for coining the term "adolescence" in the early 1900s to refer to the age span of thirteen to twenty. Erikson's continuum for this time of life is "identity versus role confusion." One characteristic of adolescents is their gregarious behavior. They love to get together in groups with other young people. It's almost as if they acknowledge a kind of herd instinct. Identity confusion persists among adolescents. One issue that is supposed to resolve in teens is identity. But few of get that nailed down well enough to hold. It usually needs further placement and tacking for years to come. Anorexia nervosa, an illness involving refusal to eat, is a problem for this age group. Young people die of it, and it is on the increase. It affects mostly young women, and very few young men. They simply stop eating or eat very little.