As I described in subsequent remarks (Bernanke, 2006), term premiums also declined during this period for reasons that are debated but may have included a perceived reduction in uncertainty regarding inflation and the real economy as well as increased demand for longer-term securities by various institutional investors, including pension funds and foreign central banks.
In particular, the weakening in investment in 2001 and 2002 was larger and lasted longer than many had anticipated, and although investment growth has picked up in recent years, the level of investment has not fully recovered from the earlier weakness.