It's for this reason that fund companies, such as Vanguard, want to make sure that our investors are good long-term investors. Yes, it is. In addition, the yields are very generous. Mortgages at this time look attractive. This relates to the issue a few questions ago, and yes, I would expect that with the surpluses and the Treasury buybacks the curve would stay inverted and oftentimes might become significantly inverted, based on the buyback size and frequency.
Duration is the amount that a bond price changes for a given change in interest rates.
There's a long formula that gets to that, which I won't explain, but in essence it measures the price sensitivity of a bond to changing interest rates. Bond funds are different than money market funds. Total Bond Market has an expense ratio of 20 basis points, and periodically it does lag its benchmark by that amount, and occasionally by more. A large part of these differences is pricing-related. The index uses Lehman's prices whereas the Vanguard portfolio uses a different pricing service, and often during periods of high price volatility, the pricing sources can result in different returns.