The Sweet Valley Twins provide a sterling instrument to understand the world around us. Not the books, the actual twins themselves. The twins are Elizabeth and Jessica, blond, smart and active. Beyond that, however, they are opposites.
- Elizabeth is sensitive and literary, and likes poetry and saving the children. She is a good student and always cares about others around her.
- Jessica is materialistic and gossipy, and is constantly involved in schemes to either sustain and improve her popularity. Her main concerns are clothing, boys and parties.
So basically, after reading enough Sweet Valley Twins books to understand Elizabeth and Jessica's psychosocial profiles (which should be about 1/5th of the way through the first book you pick up), you pretty much will be conversant with the two basic female personality types. That is, the weepy martyr and the manipulative party girl. Not that I am suggesting that all girls actually fall into this categorization system: actually, women are always personality type #2, but (based on an informal survey on AIM), they all think they are type #1.
Go figure.