The "star ratings" have become a quick way for investors to get an idea of how one fund has performed on a risk-adjusted basis versus other funds with similar objectives. The fact that Morningstar is now doing this demonstrates that ETFs have reached a critical mass in investor awareness. In order to be rated an ETF must be based in the United States and have at least a three year operating history. The ETF rating will be derived by comparing each ETF to open-end mutual funds in the same category. Although similar to traditional open-end mutual funds in many ways, a key difference is that an ETF is both priced and traded intra-day instead of only at market close. This means that investors can make more timely trading decisions as opposed to buying and selling at only whatever the closing price was for the day. With the creation of new ETF's rapidly increasing, the Morningstar "star rating" will provide investors with at least a starting point to determine whether or not they feel more in-depth research is warranted. Before investing in any ETF, investors should check with their Financial Advisors as to the appropriateness of the investment in regards to their particular situation.