Lisa Marie Simpson, commonly known as simply Lisa, is a charismatic 8-year-old girl, who exceeds the standard achievement level of children her age. Not to everyone's surprise, she is also the moral center of her family. In her upbringing, Lisa lacks parental involvement of Homer and Marge, which leads to hobbies such as a playing saxophone and guitar, riding and caring for horses, and interest in advanced studies. In school Lisa's popularity is affected by those who view her as a geeky overachiever, which leaves her with only a few friends. Lisa Simpson is a smart, witty, independent girl who focuses on her goals and strives to reach her potential, and at age 8 she is already a member of MENSA with an IQ of 159. Being siblings, Lisa and her brother Bart constantly get into brawls. However, the two have teamed up together many times, and they genuinely love each other.