I liked this bit from yesterday's NYT business section: "Sounding more like the Greenspan of old, a hard-line advocate of price stability, than his more recent incarnation as apostle of a new, technology-driven economy, the Fed chairman said that growth was on an "unsustainable trend," and warned somewhat ominously that the excesses of human nature had brought all expansions to an end."
Question. What is the constant in the econometric equations that stands for the "excesses of human nature"?