The linear dynamic lot size problem with minimum order quantity

This paper continues the analysis of a special uncapacitated single item lot sizing problem where a minimum order quantity restriction, instead of the setup cost, guarantees a certain level of production lots. A detailed analysis of the model and an investigation of the particularities of the cumulative demand structure allow us to develop a solution algorithm based on the concept of atomic sub-problems. We present an optimal solution to an atomic sub-problem in an explicit form and prove that it serves as a construction block for the optimal solution of the original problem. Computational tests and a comparison with a published algorithm confirm the efficiency of the solution algorithm developed here.     

Strategy Tradeoffs in the Knowledge and Network Economy

In traditional "value chain" firms, the main activity tradeoff is between differentiation and low cost. Increasingly, however, firms are creating customer value through networks (eg AOL) or by providing knowledge-based solutions for customers (eg venture capital firm Kleiner Perkins). This article discusses the quite different activity tradeoffs faced by these "value networks" and "value shops". It then explores the tradeoff between exploitation (focusing on short-term performance) and exploration (focusing on transcending short-term activity tradeoffs). Finally, in reviewing the implications for managers, it discusses the problem of trying to manage different types of business (value chains, networks and shops) within the same corporation.     

Time and causality: A Monte Carlo assessment of the timing-of-events approach

We present new Monte Carlo evidence regarding the feasibility of separating causality from selection within non-experimental duration data, by means of the non-parametric maximum likelihood estimator (NPMLE). Key findings are: (i) the NPMLE is extremely reliable, and it accurately separates the causal effects of treatment and duration dependence from sorting effects, almost regardless of the true unobserved heterogeneity distribution; (ii) the NPMLE is normally distributed, and standard errors can be computed directly from the optimally selected model; and (iii) unjustified restrictions on the heterogeneity distribution, e.g., in terms of a pre-specified number of support points, may cause substantial bias.     

Unemployment hysteresis and the natural rate of vacancies

On the basis of macro data from 10 OECD countries, I find that the job vacancy rate outperforms the unemployment rate as a reliable measure of domestic inflationary pressure. Moreover, while the rate of unemployment affects inflation primarily through its difference, the vacancy rate operates through a level effect as well. In most countries, a unique equilibrium rate of vacancies seems to coexist with a drifting equilibrium rate of unemployment. I show that this result is consistent with existing theories of unemployment hysteresis that focus on depreciation of human capital and search activity during unemployment spells. First version received: October 1997/Final version received: June 2001     

Density Forecasts With Midas Models

We propose a parametric block wild bootstrap approach to compute density forecasts for various types of mixed‐data sampling (MIDAS) regressions. First, Monte Carlo simulations show that predictive densities for the various MIDAS models derived from the block wild bootstrap approach are more accurate in terms of coverage rates than predictive densities derived from either a residual‐based bootstrap approach or by drawing errors from a normal distribution. This result holds whether the data‐generating errors are normally independently distributed, serially correlated, heteroskedastic or a mixture of normal distributions. Second, we evaluate density forecasts for quarterly US real output growth in an empirical exercise, exploiting information from typical monthly and weekly series. We show that the block wild bootstrapping approach, applied to the various MIDAS regressions, produces predictive densities for US real output growth that are well calibrated. Moreover, relative accuracy, measured in terms of the logarithmic score, improves for the various MIDAS specifications as more information becomes available. Copyright © 2016 John Wiley & Sons, Ltd.     

Option pricing under fast‐varying long‐memory stochastic volatility

Recent empirical studies suggest that the volatility of an underlying price process may have correlations that decay slowly under certain market conditions. In this paper, the volatility is modeled as a stationary process with long‐range correlation properties in order to capture such a situation, and we consider European option pricing. This means that the volatility process is neither a Markov process nor a martingale. However, by exploiting the fact that the price process is still a semimartingale and accordingly using the martingale method, we can obtain an analytical expression for the option price in the regime where the volatility process is fast mean reverting. The volatility process is modeled as a smooth and bounded function of a fractional Ornstein–Uhlenbeck process. We give the expression for the implied volatility, which has a fractional term structure.     

Fuel Efficiency Improvements: Feedback Mechanisms and Distributional Effects in the Oil Market

We study the interactions between fuel efficiency improvements in the transport sector and the oil market, where the efficiency improvements are policy-induced in certain regions of the world. We are especially interested in feedback mechanisms of fuel efficiency such as the rebound effect, carbon leakage and the “green paradox”, but also the distributional effects for oil producers. An intertemporal numerical model of the international oil market is introduced, where OPEC-Core producers have market power. We find that the rebound effect has a noticeable effect on the transport sector, with the magnitude depending on the oil demand elasticity. In the benchmark simulations, we calculate that almost half of the energy savings may be lost to a direct rebound effect and an additional 10% to oil price adjustments. In addition, there is substantial intersectoral leakage to other sectors through lower oil prices in the regions that introduce the policy. There is a small green paradox effect in the sense that oil consumption increases initially when the fuel efficiency measures are gradually implemented. Finally, international carbon leakage will be significant if policies are not implemented in all regions; we estimate leakage rates of 35% or higher when only major consuming regions implement fuel economy policies. Non-OPEC producers will to a larger degree than OPEC producers cut back on its oil supply as a response to fuel efficiency policies due to high production costs.     

Sufficient conditions applied to an optimal control problem of resource management

The purpose of this paper is twofold. First, by solving an interesting problem in the theory of exhaustible resources, it is exemplified how direct sufficiency conditions should properly be used in optimal control problems. The motivation for this aspect of the paper is the almost complete negligence in the economic literature of dealing properly with sufficiency conditions. Second, an important point in the discussion of J. Aarrestad (Scand. J. Econom., 81 (1979), 522–565) is supplemented.