Identification of Treatment Effects with Mismeasured Imperfect Instruments

In this article, I develop a novel identification result for estimating the effect of an endogenous treatment using a proxy of an unobserved imperfect instrument. I show that the potential outcomes distributions are partially identified for the compliers. Therefore, I derive sharp bounds on the local average treatment effect. I write the identified set in the form of conditional moments inequalities, which can be implemented using existing inferential methods. I illustrate my methodology on the National Longitudinal Survey of Youth 1979 to evaluate the returns to college attendance using tuition as a proxy of the true cost of going to college. I find that the average return to college attendance for people who attend college only because the cost is low is between 29% and 78%

Identifying Treatment Effects in the Presence of Confounded Types

In this paper, I consider identification of treatment effects whenthe treatment is endogenous. The use of instrumental variables is a popularsolution to deal with endogeneity, but this may give misleading answers whenthe instrument is invalid. I show that when the instrument is invalid due tocorrelation with the first stage unobserved heterogeneity, a second (alsopossibly invalid) instrument allows to partially identify not only the localaverage treatment effect but also the entire potential outcomes distributionsfor compliers. I exploit the fact that the distribution of the observedoutcome in each group defined by the treatment and the instrument is amixture of the distributions of interest. I write the identified set in theform of conditional moment inequalities, and provide an easily implementableinference procedure. Under some (testable) tail restrictions, the potentialoutcomes distributions are point-identified for compliers. Finally, Iillustrate my methodology on data from the National Longitudinal Survey ofYoung Men to estimate returns to college using college proximity as(potential) instrument. I find that a college degree increases the averagehourly wage of the compliers by 38-79%

Studies of fusicoccin chemistry

Imperial Users onl

Nonparametric Bounds on Treatment Effects with Imperfect Instruments

This paper extends the identification results in Nevo and Rosen(2012) to nonparametric models. We derive nonparametric bounds on the averagetreatment effect when an imperfect instrument is available. As in Nevo andRosen (2012), we assume that the correlation between the imperfect instrumentand the unobserved latent variables has the same sign as the correlationbetween the endogenous variable and the latent variables. We show that themonotone treatment selection and monotone instrumental variable restrictions,introduced by Manski and Pepper (2000, 2009), jointly imply this assumption.We introduce the concept of comonotone instrumental variable, which alsosatisfies this assumption. Moreover, we show how the assumption that theimperfect instrument is less endogenous than the treatment variable can helptighten the bounds. We also use the monotone treatment response assumption toget tighter bounds. The identified set can be written in the form ofintersection bounds, which is more conducive to inference. We illustrate ourmethodology using the National Longitudinal Survey of Young Men data toestimate returns to schooling

Working Paper 93 - The Impact of High Oil Prices on African Economies

On the one hand the high price of oil is a unique opportunity for African oil producers to use the windfall gains to speed up their development. On the other hand, it is having adverse effects on net-oil importing countries, in particular those which cannot access international capital markets to smooth out the shock. We construct a dynamic stochastic general equilibrium model, which is tailored to reflect the characteristics of African economies, to quantify the effect of the increase in the price of oil on the main macro economic aggregates. The model is general enough that it imbeds both oil producing and oil importing countries. Our results indicate that a doubling of the price of oil on world markets with complete pass through to oil consumers would lead to a 6 per cent contraction of the median net-oil importing African country in the first year. If that country were to adopt a no-pass through strategy, output would not be significantly affected but its budget deficit would increase by 6 per cent. As for the median net oil exporting country, a doubling in the price of oil would mean that its gross domestic product would increase by 4 percent under managed-float and by 9 percent under a fixed exchange rate regime. However, inflation would increase by a much greater magnitude under managed than a fixed exchange rate regime in a median net oil exporting country.

Inorganic arrangement crystal beryllium, lithium, selenium and silicon

The use of inorganic crystals technology has been widely date. Since quartz crystals for watches in the nineteenth century, and common way radio in the early twentieth century, to computer chips with new semiconductor materials. Chemical elements such as beryllium, lithium, selenium and silicon, are widely used in technology. The development of new crystals arising from that arrangement can bring technological advances in several areas of knowledge. The likely difficulty of finding such crystals in nature or synthesized, suggest an advanced study of the subject. A study using computer programs with ab initio method was applied. As a result of the likely molecular structure of the arrangement of a crystal was obtained.Comment: 33 pages, 7 figure

Electromagnetic Wave Transmission Through a Subwavelength Nano-hole in a Two-dimensional Plasmonic Layer

An integral equation is formulated to describe electromagnetic wave transmission through a sub-wavelength nano-hole in a thin plasmonic sheet in terms of the dyadic Green's function for the associated Helmholtz problem. Taking the subwavelength radius of the nano-hole to be the smallest length of the system, we have obtained an exact solution of the integral equation for the dyadic Green's function analytically and in closed form. This dyadic Green's function is then employed in the numerical analysis of electromagnetic wave transmission through the nano-hole for normal incidence of the incoming wave train. The electromagnetic transmission involves two distinct contributions, one emanating from the nano-hole and the other is directly transmitted through the thin plasmonic layer itself (which would not occur in the case of a perfect metal screen). The transmitted radiation exhibits interference fringes in the vicinity of the nano-hole, and they tend to flatten as a function of increasing lateral separation from the hole, reaching the uniform value of transmission through the sheet alone at large separations.Comment: 14 pages, 24 individual figures organized in 9 captioned group

Discordant Relaxations of Misspecified Models

In many set-identified models, it is difficult to obtain a tractable characterization of the identified set. Therefore, empirical works often construct confidence regions based on an outer set of the identified set. Because an outer set is always a superset of the identified set, this practice is often viewed as conservative yet valid. However, this paper shows that, when the model is refuted by the data, a nonempty outer set could deliver conflicting results with another outer set derived from the same underlying model structure, so that the results of outer sets could be misleading in the presence of misspecification. We provide a sufficient condition for the existence of discordant outer sets which covers models characterized by intersection bounds and the Artstein (1983) inequalities. We also derive sufficient conditions for the non-existence of discordant submodels, therefore providing a class of models for which constructing outer sets cannot lead to misleading interpretations. In the case of discordancy, we follow Masten and Poirier (2020) by developing a method to salvage misspecified models, but unlike them we focus on discrete relaxations. We consider all minimum relaxations of a refuted model which restores data-consistency. We find that the union of the identified sets of these minimum relaxations is misspecification-robust and has a new and intuitive empirical interpretation.Comment: A typo in Theorem 2 is corrected in this versio