Roger Aitken, a Forbes contributor tries to answer the question how many stock exchanges and derivative exchanges there would be in the world in the coming 3 to 5 to 10 years. In US alone there are 7 parent stock exchanges. Price and choice are two important things when it comes to investing around the world. But it in the end boils down to the most efficient model that a stock exchange can provide when it comes down to providing liquidity, speed of execution and value addition across the trading or investing life cycle. Roger does not see more than 20 stock exchanges after 10 years.