Human: What is the difference between a stock market index and a mutual fund? Assistant: 
The main difference between a stock market index and a mutual fund is that a stock market index is a statistical measure of a selection of stocks that represents a portion of the overall market, while a mutual fund is an investment vehicle that is made up of a pool of funds that are collected from multiple investors and invested in a variety of different securities including stocks, bonds, money market instruments, and other assets. The stock market index primarily measures the performance of a specified group of stocks, while a mutual fund pursues the goal of providing a return for the investor by investing their funds in a wide variety of financial instruments.