Credit Policy and Welfare

4.3 Credit Policy and Welfare

We have seen from Figure 5 that credit policy can be used to stabilize the economy, most notably in response to purely financial disturbances that shift the ¯ ω t (L) schedule. But is it desirable to do so, and to what extent? Our model can also be used to consider the optimal use of this additional dimension of policy, if we are willing to suppose that the prudential arguments against the central bank’s involvement in the allocation of credit should not be determinative, at least in the case of sufficiently severe financial disruptions. In our model, an increase in L cb

t can improve welfare on two grounds: for a given volume of private borrowing

b t , an increase in L cb t allows the volume of private lending L t to fall, which should reduce both the resources Ξ p

t consumed by the intermediary sector and the equilibrium credit spread

52 That is, ¯ ω 0 (¯ L) is increased by 12 percentage points per annum.

ω t (due to equilibrium relation (2.9)). Under plausible conditions, our model implies both

a positive shadow value ϕ Ξ,t of reductions in Ξ t (the Lagrange multiplier associated with the resource constraint (2.2)) and a positive shadow value ϕ ω,t of reductions in ω t ; hence an increase in L cb t should be desirable on both grounds. In the absence of any assumed cost of central-bank credit policy, one can easily obtain the result that it is always optimal for the central bank to lend in amount sufficient to allow an equilibrium with L t = 0, i.e., the central bank should substitute for private credit markets altogether. Of course, we do not regard this as a realistic conclusion. As a simple way of introducing into our calculations the fact that the central bank is unlikely to have a comparative advantage at the activity of credit allocation under normal circumstances, we

cb assume that central-bank lending consumes real resources in a quantity Ξ cb (L t ), by analogy with our assumption that real resources Ξ p

t are consumed by private intermediaries. The function Ξ cb (L) is assumed to be increasing and at least weakly convex; in particular, we assume that Ξ cb′ (0) > 0, so that there is a positive marginal resource cost of this activity, even

when the central bank starts from a balance sheet made up entirely of Treasury securities.

The first-order conditions for optimal choice of L cb t then become:

(4.5) together with the complementary slackness condition that at least one of conditions (4.4) or

L cb

t ≥ 0,

(4.5) must hold with equality in each period. (Here the first expression in square brackets in (4.4) is the partial derivative of Ξ cb

t with respect to L t , holding constant the value of total borrowing b t , while the second expression in square brackets is the partial derivative of ω t with respect to L cb t under the same assumption.)

A “Treasuries only” policy is optimal in the event of a corner solution, in which (4.4) is an inequality, as will be the case if Ξ cb′ (0) is large enough. In our view, it is most reasonable to calibrate the model so that this is true in steady state. Then not only will the optimal policy involve “Treasuries only” in the steady state, but (assuming that the inequality is strict at the steady state) this will continue to be true in the case of any stochastic disturbances that

are small enough. However, it will remain possible for the optimal policy to require L cb t >0 are small enough. However, it will remain possible for the optimal policy to require L cb t >0

However, not all “purely financial” disturbances — by which we mean exogenous shifts in the functions ¯ p Ξ

t (L) or χ t (L) of a type that increase the equilibrium credit spread ¯ ω t (L) for a given volume of private credit — are equally likely to justify an active central-bank

credit policy on the grounds just mentioned. In fact, the optimal credit policy response to a given shift in the function ¯ ω t (L) depends greatly on the source of the shift. 53 To illustrate this, we consider the quantitative effects of alternative types of purely financial disturbances in our calibrated model.