One way in which corporate financial structure affects macroeconomic performance is by creating debt overhang. Debt overhang occurs when existing debt deters new investment because the benefits from new investment will go to the existing creditors, not to the new investors. If the economy is booming, debt overhang will not bind because the returns to investing are high. If the economy is stagnant, debt overhang will bind because the returns to investing are low. As a result, high levels of debt can create multiple expectational equilibria in which "animal spirits" determine economy activity.

One way in which corporate financial structure affects macroeconomic performance is by creating debt overhang. Debt overhang occurs when existing debt deters new investment because the benefits from new investment will go to the existing creditors, not to the new investors. If the economy is booming, debt overhang will not bind because the returns to investing are high. If the economy is stagnant, debt overhang will bind because the returns to investing are low. As a result, high levels of debt can create multiple expectational equilibria in which 'animal spirits' determine economy activity.

We document that net equity issuance is considerably more sensitive to aggregate stock returns and Q's than to firm-level stock returns and Q's. Very similar patterns also emerge when we look at merger activity. In light of earlier work (Campbell 1991, Vuolteenaho 2002) which finds that aggregate stock returns are less informative about future cashflows than are firm-level stock returns--and thus, potentially more strongly influenced by investor sentiment--these results suggest that both equity issuance and mergers are to a significant extent driven by market-timing considerations, as opposed to by purely fundamental factors.

We examine some basic data on the evolution of aggregate short interest, both during the dot-com era, and at other times in history. Total short interest moves in a countercyclical fashion. For example, short interest in NASDAQ stocks actually declines as the NASDAQ index approaches its peak. Moreover, this decline does not seem to reflect a substitution away from outright short-selling and towards put options, as the ratio of put-to-call volume displays the same countercyclical tendency. The evidence suggests that: i) arbitrageurs are reluctant to bet against aggregate mispricings; and ii) short-selling does not play a particularly helpful role in stabilizing the overall stock market.