today I came across an expression my college claims it tells us about the average index value i of a random variable Xi. The expression is:

\(\displaystyle AI = \frac{\sum_{i}^{n} i \times X_{i}}{\sum_{i}^{n} X_{i}}\)

However I am having problems understanding it, especially the part about dividing the whole thing with sum of Xi. Could anyone clarify the expression or at least give hers/his own opinion about what AI means/is/stands for?

thank you

baxy