The papers collected in this issue are united in a common view that it is rational to recognize that we have a poor perception of the constraints we face when making economic decisions and hence we employ decision rules that are robust. Robustness can be interpreted in different ways but generally it implies that our decision rules should not depend critically on an exact description of these constraints but they should perform well over a prespecified range of potential variations in the assumed economic environment. So, we are interested in deriving optimal and hence rational decisions where our utility or loss function incorporates the need for robustness in the face of a misspecified model. This misspecification can involve placing simple bounds on deviations from the parameters we assume for a nominal model, or misspecified dynamics, neglected nonlinearities, time variation, or quite general arbitrary misspecification in the transfer function between the input uncertainties and the output variables in which we are ultimately interested.

This paper investigates the degree of comovements in quarterly Italian time series of sectoral output. A recently developed multivariate technique for the empirical analysis of long-run, cyclical and seasonal comovements is used in the context of a multisectoral real-business-cycle model augmented with persistent seasonal shocks in productivity. Our empirical results emphasize the role of input–output relations in the propagation mechanism and indicate that sectoral outputs have a relatively low number of common stochastic trends, in conflict with the hypothesis of independent productivity shocks. In contrast, stochastic seasonals seem to move idiosyncratically. Furthermore, our findings suggest that the theoretical model should be extended to allow for deterministic seasonal shifts in preferences.

This paper analyzes the dependence of average consumption on the saving rate in a one-sector neoclassical Solow growth model with production shocks and stochastic rates of population growth and depreciation where arbitrary ergodic processes are considered. We show that the long-run behavior of the stochastic capital intensity, and hence average consumption along any sample path, is uniquely determined by a random fixed point that depends continuously on the saving rate. This result enables us to prove the existence of a golden-rule saving rate that maximizes average consumption per capita. We also show that the golden-rule path is dynamically efficient. The results are illustrated numerically for Cobb–Douglas and CES production functions.

This paper analyzes optimal paths in a one-sector growth model when the technology is not convex. In such a case, we prove that optimal paths converge to the upper steady state iff the initial wealth is above a critical level. Then, we first show that, thanks to debt and/or R&D, the poverty trap may be avoided. Second, we introduce a distortion: corruption that mostly has dramatic consequences on growth, but may have a beneficial effect if it is not high and if it improves productivity (incentive effect).

We present a model of endogenous growth in which government consumption and production services are financed by distorting capital taxes. We generalize Barro's public finance model of growth in two ways. First, we study the properties, and the role in growth, of a wider menu of second-best optimal policies, namely, the capital tax rate and the portion of total tax revenues used to finance public production services versus public consumption services. Second, we investigate the possibility of the existence and uniqueness of a long-run equilibrium in which optimal policies do not change and the economy grows at a constant balanced growth path, as well as the possibility of dynamic determinacy of this long-run equilibrium.

The paper discusses a simple univariate nonlinear parametric time-series model for unemployment rates, focusing on the asymmetry observed in many OECD unemployment series. The model is based on a standard logistic smooth transition autoregressive model for the first difference of unemployment, but it also includes a lagged level term. This model allows for asymmetric behavior by permitting “local” nonstationarity in a globally stable model. Linearity tests are performed for a number of quarterly, seasonally unadjusted, unemployment series from OECD countries, and linearity is rejected for a number of them. For a number of series, nonlinearity found by testing can be modeled satisfactorily by use of our smooth transition autoregressive model. The properties of the estimated models, including persistence of the shocks according to them, are illustrated in various ways and discussed. Possible existence of moving equilibria in series not showing asymmetry is investigated and modeled with another smooth transition autoregressive model.

It is common to interpret rejections of the unit-root null hypothesis in favor of a trend stationary process with possible trend breaks as evidence that the data are better characterized as stationary about a broken trend. This interpretation is valid only if the model postulated under the alternative hypothesis is the only plausible alternative to the model postulated under the null. We argue that there are economically plausible models that are not well captured under either the null hypothesis or the alternative hypothesis of these tests. We show that applied researchers who ignore this possibility are likely to reject the unit-root null with high probability in favor of a trend stationary process with possible breaks. Our evidence shows that this potential pitfall is both economically relevant and quantitatively important. We explore the extent to which applied users may mitigate inferential errors by using finite-sample and bootstrap critical values.

The lack of a supranational legal authority that can enforce private contracts across borders makes debt repayment in an international setting contingent on borrowers' willingness to pay rather than ability to pay. This market failure (i.e., inadequate enforcement) causes investment to fall short of its unconstrained level. This paper examines how foreign aid affects a country's willingness to honor private investment agreements. We consider two types of aid: technical assistance and loan subsidies. We show that when enforcement is inadequate, aid has the following effects: (i) it reduces default risk, promotes capital flows, and can, in principle, restore investment to its unconstrained level; (ii) when default risk is high, aid can increase the welfare of both the recipient and the donor country. Thus, foreign aid serves as an enforcement mechanism in an international setting. This provides a nonaltruistic rationale for foreign aid. Finally, we discuss the implications of providing bilateral versus multilateral aid (e.g., by individual countries versus multilateral organizations).

The theme of this paper is that the simple concept of risk sensitivity raises ideas, shows associations, and forces clarification of issues that one would have thought quite unrelated.

This paper examines an economy in which output is produced by state-owned enterprises and private firms. Private-capital formation requires intermediation that is subject to a credit market friction. In this environment, I look at the effects of a privatization policy that transfers state-owned capital to the private sector. Multiple steady-state equilibria are possible. When these arise, the low-wage equilibrium features a relatively inefficient financial system and privatization transfers help to increase the aggregate capital stock by reducing the severity of the credit market frictions. On the other hand, privatization transfers may have adverse effects when the economy is at the high-wage equilibrium. Analysis of the dynamic characteristics of the model reveals that development trap phenomenon and endogenous fluctuations can be observed.

We review several control problems, all related to robust control in some way, that lead to a minimax linear quadratic problem. We stress the fact that although an augmented performance index appears, containing an L2 norm of a disturbance signal, only the nonaugmented quadratic performance index is of interest per se in each case.

This paper examines the quantitative implications of government fiscal policy in a discrete-time one-sector growth model with a productive externality that generates social increasing returns to scale. Starting from a laissez-faire economy that exhibits local indeterminacy, we show that the introduction of a constant capital tax or subsidy can lead to various forms of endogenous fluctuations, including stable 2-, 4-, 8-, and 10-cycles, quasiperiodic orbits, and chaos. In contrast, a constant labor tax or subsidy has no effect on the qualitative nature of the model's dynamics. We show that the use of local steady-state analysis to detect the presence of multiple equilibria in this class of models can be misleading. For a plausible range of capital tax rates, the log-linearized dynamical system exhibits saddle-point stability, suggesting a unique equilibrium, whereas the true nonlinear model exhibits global indeterminacy. This result implies that stabilization policies designed to suppress sunspot fluctuations near the steady state may not prevent sunspots, cycles, or chaos in regions away from the steady state. Overall, our results highlight the importance of using a model's nonlinear equilibrium conditions to fully investigate global dynamics.

We use a log-normal framework to examine the effect of preferences on the market price for risk, that is, the Sharpe ratio. In our framework, the Sharpe ratio can be calculated directly from the elasticity of the stochastic discount factor with respect to consumption innovations as well as the volatility of consumption innovations. This can be understood as an analytical shortcut to the calculation of the Hansen–Jagannathan volatility bounds, and therefore provides a convenient tool for theorists searching for models capable of explaining asset-pricing facts. To illustrate the usefulness of our approach, we examine several popular preference specifications, such as CRRA, various types of habit formation, and the recursive preferences of Epstein–Zin–Weil. Furthermore, we show how the models with idiosyncratic consumption shocks can be studied.

We develop a test of evolutionary change that incorporates a null hypothesis of homogeneity, which encompasses time invariance in the variance and autocovariance structure of residuals from estimated econometric relationships. The test framework is based on examining whether shifts in spectral decomposition between two frames of data are significant. Rejection of the null hypothesis will point not only to weak nonstationarity but to shifts in the structure of the second-order moments of the limiting distribution of the random process. This would indicate that the second-order properties of any underlying attractor set has changed in a statistically significant way, pointing to the presence of evolutionary change. A demonstration of the test's applicability to a real-world macroeconomic problem is accomplished by applying the test to the Australian Building Society Deposits (ABSD) model.

This paper investigates the impact of anticipated inflation on features of the business cycle in the presence of recursive but intertemporally dependent tastes. Intertemporal dependence is induced by the presence of a variable or endogenous individual rate of time preference. Quantitative experiments indicate that variability in the rate of time preference can enhance the contribution of monetary shocks to the fluctuations of real variables. Another implication of the variable-time-preference model is that, unlike the fixed time preference model, the business cycle features in high inflation and low inflation economies can be very different. The contribution of monetary shocks to fluctuations increases partly because endogenous time preference accentuates inflation-tax effects, which are already present in the standard framework because of the presence of cash-in-advance constraints. The change in the relative role of monetary shocks is also related to how variable time preference alters the effects of technology shocks, which can be quantitatively or qualitatively different in comparison to the standard model, depending on the parameters of the model.

We investigate the optimal path of the primary surplus that a government will choose to minimize costs that derive from exceeding the Maastricht criteria and generally of a “stability pact,” where we assume three components of costs that are related to (1) the debt-to-GDP ratio, (2) the overall deficit-to-GDP ratio, and (3) the acceptance level of savings in the economy. We show that various political-economic settings can result in completely different equilibrium strategies of the debt-to-GDP ratio and the primary deficit. The spectrum of possible optimal strategies ranges from no stationary solutions to multiple equilibrium and cyclical solutions and from positive to negative levels of the optimal debt-to-GDP ratio. Our results emphasize the importance of macroeconomic and behavioral (acceptance rate of a policy) variables in order to explain complex economic time series.

If one drops the strong assumption that firms and households know all of the relevant parameters, and instead models agents as learning these parameters, the estimated parameters become random variables. Taking expectations several periods into the future may then involve taking the expectation of a product of random variables. Because the resulting problem is difficult, previous research has avoided it. This paper makes some progress using both analytical and numerical techniques. Focusing especially on consumption, we find that the resulting covariance terms could account for the well-documented empirical result that consumption displays excess sensitivity to lagged income. We show that a similar covariance effect could play a role in many widely used economic models.

This paper investigates conditions under which a long-run recursive model can be used to identify a structure. Economists frequently employ this type of empirical model. I define the class of long-run partially recursive structures. If an economic system is a member of this class, then certain long-run recursive empirical models will obtain some of the structural impulse response functions. This sufficient condition for a structure is first shown in a vector autoregression. A well-known example from the literature is used to illustrate this particular class of structures and to present some useful applications of the result. Then the result is shown in models of cointegrated time series. Necessary conditions for a long-run recursive model to identify structure are addressed in the conclusion.

A planner and agent in a permanent-income economy cannot observe part of the state, regard their model as an approximation, and value decision rules that are robust across a set of models. They use robust decision theory to choose allocations. Equilibrium prices reflect the preference for robustness and so embody a “market price of Knightian uncertainty.” We compute market prices of risk and compare them with a model that assumes that the state is fully observed. We use detection error probabilities to constrain a single parameter that governs the taste for robustness.

In recent decades, the structure of wages in the U.S. economy has shifted to favor workers with college degrees over those without college degrees. Concurrently, there has been an increase in the share of the workforce that is college educated. We build an overlapping generations model in which skill-biased technological change drives both rising wage inequality and a rising percentage of skilled (educated) workers in the labor force. We explore the implications for agent welfare and for the distribution of income of different factor taxation choices. We find that higher tax rates on capital and lower tax rates on unskilled labor can yield steady-state welfare gains across a heterogeneous population, and that these gains increase as the economy experiences technological change that favors skilled labor. Moreover, these shifts in taxation can lower net wage inequality. Steady-state welfare gains, however, come at the expense of agents alive upon implementation.