This paper summarizes what is known about the impact of public–private partnerships (PPPs) in the three sectors where they have been used intensively: infrastructure (energy, transport, water and sanitation, and telecommunications), education, and health. It lays out the main elements of economic theory relevant to analyzing the trade-off between PPPs and the public provision of complex projects. It places PPPs within a historical perspective. It reviews empirical evaluations of the effectiveness of PPPs and, whenever possible, the implications for social outcomes. Finally, it draws conclusions on cross-cutting issues that influence the efficiency of PPPs, from contract design and regulation to renegotiations and institutional issues. The paper straightens out and qualifies the record of existing evidence and signals some of the main areas and topics for future fruitful research.

We develop a theory of endogenous uncertainty in which the ability of investors to learn about firm-level fundamentals is impaired during financial crises. At the same time, higher uncertainty reinforces financial distress. Through this two-way feedback loop, a temporary financial shock can cause a persistent reduction in risky lending, output, and employment that coincides with increased uncertainty, default rates, credit spreads, and disagreement among forecasters. We embed our mechanism into standard real business cycle and New-Keynesian models and show how it generates endogenous and internally persistent processes for the efficiency and labour wedges.

This paper argues that limited asset market participation is crucial in explaining U.S. macroeconomic performance and monetary policy before the 1980s and their changes thereafter. In an otherwise conventional sticky-price model, standard aggregate demand logic is inverted at low enough asset market participation: interest rate increases become expansionary, and passive monetary policy ensures equilibrium determinacy and maximizes welfare. This suggests that Federal Reserve policy in the pre-Volcker era was better than conventional wisdom implies. We provide empirical evidence consistent with this hypothesis and study the relative merits of changes in structure and shocks for reproducing the conquest of the Great Inflation and the Great Moderation.

According to the Chamley-Judd result, capital should not be taxed in the long run. In this paper, we overturn this conclusion, showing that it does not follow from the very models used to derive it. For the main model in Judd (1985), we prove that the long-run tax on capital is positive and significant, whenever the intertemporal elasticity of substitution is below one. For higher elasticities, the tax converges to zero but may do so at a slow rate, after centuries of high tax rates. The main model in Chamley (1986) imposes an upper bound on capital taxes. We provide conditions under which these constraints bind forever, implying positive long-run taxes. When this is not the case, the long-run tax may be zero. However, if preferences are recursive and discounting is locally nonconstant (e.g., not additively separable over time), a zero long-run capital tax limit must be accompanied by zero private wealth (zero tax base) or by zero labor taxes (first-best). Finally, we explain why the equivalence of a positive capital tax with ever-increasing consumption taxes does not provide a firm rationale against capital taxation.

We propose a theory of indebted demand, capturing the idea that large debt burdens lower aggregate demand, and thus the natural rate of interest. At the core of the theory is the simple yet underappreciated observation that borrowers and savers differ in their marginal propensities to save out of permanent income. Embedding this insight in a two-agent perpetual-youth model, we find that recent trends in income inequality and financial deregulation lead to indebted household demand, pushing down the natural rate of interest. Moreover, popular expansionary policies—such as accommodative monetary policy—generate a debt-financed short-run boom at the expense of indebted demand in the future. When demand is sufficiently indebted, the economy gets stuck in a debt-driven liquidity trap, or debt trap. Escaping a debt trap requires consideration of less conventional macroeconomic policies, such as those focused on redistribution or those reducing the structural sources of high inequality.

We study a real small open economy with two key ingredients (1) partial segmentation of home and foreign bond markets and (2) a pecuniary externality that makes the real exchange rate excessively volatile in response to capital flows. Partial segmentation implies that, by intervening in the bond markets, the central bank can affect the exchange rate and the spread between home- and foreign-bond yields. Such interventions allow the central bank to address the pecuniary externality, but they are also costly, as foreigners make carry trade profits. We analytically characterize the optimal intervention policy that solves this trade-off: (1) the optimal policy leans against the wind, stabilizing the exchange rate; (2) it involves smooth spreads but allows exchange rates to jump; (3) it partly relies on “forward guidance,” with non-zero interventions even after the shock has subsided; (4) it requires credibility, in that central banks do not intervene without commitment. Finally, we shed light on the global consequences of widespread interventions, using a multi-country extension of our model. We find that, left to themselves, countries over-accumulate reserves, reducing welfare and leading to inefficiently low world interest rates.

We develop a tractable framework for deficit and debt dynamics. A “free lunch” fiscal deficit—one that raises spending without higher future taxes—is sustainable without zero lower bound (ZLB) only when R < G − φ, where φ is the sensitivity of the interest rate to the debt level. With the ZLB, both high and low deficits can increase debt, as the latter weaken demand and reduce nominal growth at the ZLB. A rise in income inequality expands fiscal space outside the ZLB, but contracts it at the ZLB. Calibrating the model, we find little space for “free lunch” policies for the United States in 2019, but significant space for Japan.

How much did fiscal policy contribute to euro area real GDP growth during the Great Recession? We estimate that discretionary fiscal measures have increased annualized quarterly real GDP growth during the crisis by up to 1.6 percentage points. We obtain our result by using an extended version of the European Central Bank's New Area-Wide Model with a rich specification of the fiscal sector. A detailed modeling of the fiscal sector and the incorporation of as many as eight fiscal time series appear pivotal for our result.

We analyze a dynamic credit market where banks choose lending standards, modeled as costly effort to screen out bad borrowers. Tighter standards worsen the borrower pool, increasing banks’ incentives to employ tight standards in the future. This dynamic complementarity in lending standards can amplify and prolong downturns, decreasing lending and increasing credit spreads. Because lending standards have negative externalities, the market can converge to a steady state with inefficiently tight lending standards. We discuss the role of optimal policy to avoid this outcome as well as the impact of balance sheet costs on lending standards.

We develop a system of disaggregated economic accounts. The system breaks down national accounting positions into bilateral flows between consistently defined groups of consumers (consumer cells), groups of producers (producer cells), the government, and the rest of the world. We disaggregate the full circular flow of money, including consumer spending, labor compensation, firm profits, intermediates trade, foreign trade, and government transactions, while satisfying all national accounting identities. We implement the disaggregated system for small region-by-industry cells in Denmark and present stylized facts, such as variation in domestic spending, local and urban bias in consumer spending, and a pattern of triangular flows across regions. Cell-level measures of spending intensity capture how much spending by a cell contributes to the income of cells experiencing unemployment after a shock. Using a general equilibrium model, we show that fiscal transfers raise aggregate GDP by more when they target cells with high spending intensity on unemployed cells. The disaggregated economic accounts help governments select more effective policies.