Extensive Margins and the Demand for Money at Low Interest Rates
发现美国多数家庭的关键决策不是持有多少生息资产，而是是否持有；利率与资产总量的乘积决定这一决策，并利用1989年消费者金融调查数据估计了低利率下货币需求的利率弹性。
We argue that the relevant monetary decision for the majority of U.S. households is not the fraction of assets to be held in interest-bearing form, but whether to hold any such assets at all (we call this "the decision to adopt" the financial technology). We show that the key variable governing the adoption decision is the product of the interest rate times the total amount of assets. This implies that the interest elasticity of household money demand at low interest rates can be estimated from the variation in asset holdings in a cross section of households rather than historical interest rate variations. We do so with the 1989 Survey of Consumer Finances. We find that (a) the elasticity of money demand is very small when the interest rate is small, (b) the probability that a household holds any amount of interest-bearing assets is positively related to the level of financial assets, and (c) the cost of adopting financial technologies is negatively related to participation in a pension program. At interest rates of 5 percent, roughly one-half of the elasticity can be attributed to the Allais-Baumol-Tobin or intensive margin and half to the new adopters or extensive margin. The intensive margin is less important at lower interest rates and more important at higher interest rates. Finally, we argue that ignoring extensive margins may lead to an empirically important overestimation of the cost of inflation at low interest rates.