4.) Statistical: All statisticians know the concept of the bell curve or the normal distribution. It has particular properties and is most popular in the academic arena. A score of 100 is average and 66% of the population score between 85 and 115 and around 97% between 70 and 130. Thus if you score below 70 and over 130 you are unusual: extreme, though the word abnormal would not be applied. This model has drawbacks; just because behavior occurs frequently does not necessarily make it healthy or desirable. Also, while it may work for abilities which are reasonably straight forward to measure, it deals less easily with more subtle and multi-dimensional issues like personality or mental illness.