When choosing an investment for the core portion of your portfolio many analysts will recommend an index fund. Companies that offer index funds to investors are increasingly offering a version of the fund that is organized as an exchange-traded fund or ETF (Vanguard Total Bond Market Index Fund and Vanguard Total Bond Market ETF would be an example). While the underlying investments are substantially the same, there are enough differences between the two to make one advantageous over the other depending upon your circumstances.There are two main differences between an index fund and an ETF – how they’re traded and costs.An index fund is organized as a typical mutual fund. An investor can place a buy or sell order at anytime and that order will be completed at the next available close o