As the pressure for higher mortgage rates has increased in recent weeks, investors have speculated that the Fed would step in to "defend" certain interest rate levels, but that hasn't happened. This week, Fed officials explained that their mortgage-backed securities (MBS) purchases are designed to support the mortgage market and not to set rates. The Fed's MBS purchases of $25.5 billion this week were similar to levels seen in recent weeks. Disappointed that the Fed hasn't increased its quantity of asset purchases, investors sold MBS this week, and mortgage rates moved higher.

A number of factors have been developing which typically push interest rates higher. The coming supply of debt needed to pay for government programs will compete for investor funds. Despite strong demand for this week's large Treasury auctions, investors are concerned that higher rates will be required in the future. In addition, an improved economic outlook has made investors more willing to move funds to riskier assets and away from safer assets such as bonds. It also means that higher inflation may be a concern sooner than previously expected.

The difference between short-term and long-term rates reached record spreads during the week. With the Fed-controlled fed funds rate close to zero, short-term rates remained low. Long-term rates, which are market-controlled and influenced by investor expectations, rose significantly. A wide yield curve spread is often found during periods when the economy is strengthening.