Instrumental variable estimation based on grouped data

The paper considers the estimation of the coefficients of a single equation in the presence of dummy intruments. We derive pseudo ML and GMM estimators based on moment restrictions induced either by the structural form or by the reduced form of the model. The performance of the estimators is evaluated for the non-Gaussian case. We allow for heteroscedasticity. The asymptotic distributions are based on parameter sequences where the number of instruments increases at the same rate as the sample size. Relaxing the usual Gaussian assumption is shown to affect the normal asymptotic distributions. As a result also recently suggested new specification tests for the validity of instruments depend on Gaussianity. Monte Carlo simulations confirm the accuracy of the asymptotic approach.

Instrumental Variable Estimation Based on Grouped Data

The paper considers the estimation of the coefficients of a single equation in the presence of dummy intruments. We derive pseudo ML and GMM estimators based on moment restrictions induced either by the structural form or by the reduced form of the model. The performance of the estimators is evaluated for the non-Gaussian case. We allow for heteroscedasticity. The asymptotic distributions are based on parameter sequences where the number of instruments increases at the same rate as the sample size. Relaxing the usual Gaussian assumption is shown to affect the normal asymptotic distributions. As a result also recently suggested new specification tests for the validity of instruments depend on Gaussianity. Monte Carlo simulations confirm the accuracy of the asymptotic approach.

Is There Really a Green Paradox?

The Green Paradox states that, in the absence of a tax on CO2 emissions, subsidizing a renewable backstop such as solar or wind energy brings forward the date at which fossil fuels become exhausted and consequently global warming is aggravated. We shed light on this issue by solving a model of depletion of non-renewable fossil fuels followed by a switch to a renewable backstop, paying attention to timing of the switch and the amount of fossil fuels remaining unexploited. We show that the Green Paradox occurs for relatively expensive but clean backstops (such as solar or wind), but does not occur if the backstop is sufficiently cheap relative to marginal global warming damages (e.g., nuclear energy) as then it is attractive to leave fossil fuels unexploited and thus limit CO2 emissions. We show that, without a CO2 tax, subsidizing the backstop might enhance welfare. If the backstop is relatively dirty and cheap (e.g., coal), there might be a period with simultaneous use of the non-renewable and renewable fuels. If the backstop is very dirty compared to oil or gas (e.g., tar sands), there is no simultaneous use. The optimum policy requires an initially rising CO2 tax followed by a gradually declining CO2 tax once the dirty backstop has been introduced. We also discuss the potential for limit pricing when the non-renewable resource is owned by a monopolist.Green Paradox, Hotelling rule, non-renewable resource, renewable backstop, global warming, carbon tax, limit pricing

Too Little Oil, Too Much Coal: Optimal Carbon Tax and when to Phase in Oil, Coal and Renewables

Our main message is that it is optimal to use less coal and more oil once one takes account of coal being a backstop which emits much more CO2 than oil. The way of achieving this is to have a steeply rising carbon tax during the initial oil-only phase, a less-steeply rising carbon tax during the intermediate phase where oil and coal are used alongside each other and the following coal-only phase, and a flat carbon tax during the final renewables-only phase. The “laissez-faire” outcome uses coal forever or starts with oil until it is no longer cost-effective to do so and then switches to coal. We also analyze the effects on the optimal transition times and carbon tax of a carbon-free, albeit expensive backstop (solar or wind energy). Subsidizing renewables to just below the cost of coal does not affect the oil-only phase. The gain in green welfare dominates the welfare cost of the subsidy if the subsidy gap is small and the global warming challenge is acute. Without a carbon tax a prohibitive coal tax leads to less oil left in situ and substantially delays introduction of renewables, but curbs global warming substantially as coal is never used. Finally, we characterize under general conditions what the optimal sequencing oil and coal looks like.Hotelling rule, non-renewable resource, dirty backstop, coal, global warming, carbon tax, renewables, tax on coal, subsidy on renewables, transition times, Herfindahl rule

Efficiency bounds for instrumental variable estimators under group-asymptotics

This paper introduces a general, formal treatment of dynamic constraints, i.e., constraints on the state changes that are allowed in a given state space. Such dynamic constraints can be seen as representations of "real world" constraints in a managerial context. The notions of transition, reversible and irreversible transition, and transition relation will be introduced. The link with Kripke models (for modal logics) is also made explicit. Several (subtle) examples of dynamic constraints will be given. Some important classes of dynamic constraints in a database context will be identified, e.g. various forms of cumulativity, non-decreasing values, constraints on initial and final values, life cycles, changing life cycles, and transition and constant dependencies. Several properties of these dependencies will be treated. For instance, it turns out that functional dependencies can be considered as "degenerated" transition dependencies. Also, the distinction between primary keys and alternate keys is reexamined, from a dynamic point of view.

Rans-based optimization of the aft part of ships including free surface effects

A procedure for optimizing the aft body of a ship for minimal power and best wake field quality is described, based on full-scale RANS computations possibly including free- surface effects. A flexible and effective definition of parametric hull form variations is used, based on interpolation between a limited number of basis hull forms. This keeps the dimension of the search space low, which enables to do systematic variations. For a test case in which the ship’s wave making can be neglected it is shown that the grid dependence in the computed trends is low, and for a test case including free-surface effects it is demonstrated how the search space can be set up in such a way that a considerable decrease in required power can be obtained without spoiling the wake quality

Optimal carbon tax with a dirty backstop: Oil, coal, or renewables?

Optimal climate policy is studied. Coal, the abundant resource, contributes more CO2 per unit of energy than the exhaustible resource, oil. We characterize the optimal sequencing oil and coal and departures from the Herfindahl rule. 'Preference reversal' can take place. If coal is very dirty compared to oil, there is no simultaneous use. Else, the optimal outcome starts with oil, before using oil and coal together, and finally coal on its own. The 'laissez-faire' outcome uses coal forever or starts with oil until it is no longer profitable to do so and then switches to coal. The optimum requires a steeply rising CO2 tax during the oil-only phase and a less steeply rising CO2 tax during the subsequent oil-coal and coal-only phases to avoid the abrupt switch from oil to coal thus leaving a lot of oil in situ. Finally, we analyze the effects on the optimal transition times and carbon tax of a carbon-free, albeit expensive backstop (solar or wind). Without a carbon tax, a prohibitive coal tax leads to less oil in situ, substantially delays introduction of renewable, and thus curbs global warming substantially. Subsidizing renewables to just below the cost of coal does not affect the oil-only phase. The gain in green welfare dominates the welfare cost of the subsidy if the subsidy gap is small and the global warming challenge is acute