Showing papers by "Instituto Tecnológico Autónomo de México published in 1998"
TL;DR: In this paper, the authors consider a model with two logarithmic utility maximizer agents that observe aggregate consumption but disagree about its expected rate of change, and show that volatility of the interest rate in an economy with additional information is higher.
207 citations
TL;DR: The epidemiological background, clinical details and surgical outcome of patients presenting with urogenital fistulae to St Luke's Hospital, Uyo, and the associated VVF Unit at Mbribit Itam, Nigeria, between January 1970 and December 1994 are determined.
Abstract: The aim of the study was to determine the epidemiological background, clinical details and surgical outcome of patients presenting with urogenital fistulae to St Luke's Hospital, Uyo, and the associated VVF Unit at Mbribit Itam, Akwa Ibom State, Nigeria, between January 1970 and December 1994. A retrospective review of hospital operating theater records and case notes was carried out. Clinical details and outcome were assessed for the total cohort of 2484 patients. Epidemiological data were extracted from the case notes of 715 patients presenting between January 1990 and December 1994. Of these 92.2% were of obstetric etiology, 80.3% following neglected obstructed labor, 6.9% following cesarean section, and 5.0% followed ruptured uterus; 4.4% followed pelvic surgery and the remaining 3.4% of miscellaneous causes included malignancy, coital injury, infection and trauma; 8% had a coexisting rectovaginal fistula or third-degree perineal tear. Only 37.3% of patients were aware of their age; the median age of this group was 28 years. Literacy was difficult to judge reliably, although 29% were able to sign their name. Parity ranged from 0 to 17, and only 31.4% of fistulae related to first pregnancies. Although 73.1% were delivered in hospital, in 97.1% labor was initially managed at home, with a traditional birth attendant, in a maternity home, or in church; 34.1% were delivered by cesarean section, although the live-birth rate was only 10.3% in the causative pregnancy. For a variety of reasons 124 women were not operated upon: 1954 underwent only one operation, giving a presumptive cure rate at first operation of 81.2%; 247 underwent two, 116 three, 32 four, and 11 five operations during the study period. The ultimate closure rate was 97.7%, with only 0.6% undergoing urinary diversion. The type and distribution of fistulae recorded in this series is consistent with previous series of largely obstetric fistulae from the developing world. Surgical cure rates are also comparable. The epidemiological background is at variance with previous reports in several respects; this may reflect biosocial differences in the population studied.
178 citations
TL;DR: In this paper, a nonparametric test for I(0) against fractional alternatives is proposed, which makes no assumptions on spectral behaviour away from zero frequency, and seems likely to have good efficiency.
Abstract: There is frequently interest in testing that a scalar or vector time series is I(0), possibly after first- differencing or other detrending, while the I(0) assumption is also taken for granted in autocorrelation-consistent variance estimation. We propose a test for I(0) against fractional alternatives. The test is non-parametric, and indeed makes no assumptions on spectral behaviour away from zero frequency. It seems likely to have good efficiency against fractional alternatives, relative to other nonparametric tests. The test is given large samle justification, subjected to a Monte Carlo analysis of finite sample behaviour, and applied to various empirical data series.
167 citations
TL;DR: In this article, the authors consider a small open economy with a costly state verification problem and binding reserve requirements and show that sufficiently large increases in money growth or the world interest rate can transform the high activity steady state from a sink to a source.
155 citations
TL;DR: In this article, the authors show that the conventionally accepted view that higher saving rate causes higher economic growth does not hold for Mexico, in fact, the causality goes in the opposite direction.
112 citations
TL;DR: In this paper, the effects of labor and capital income taxation on the transitional dynamics to the balanced path of the economy were studied. And the authors considered the taxation welfare cost in two non-trivial generalizations of their basic model which include the case of physical capital in the educational sector and leisure as an additional argument in the utility function.
75 citations
TL;DR: A CUSUM chart based on the subgroup range is proposed and it is found that for small subgroup sizes it has an excellent performance and it thus represents a powerful alternative to currently utilized strategies.
Abstract: When monitoring a process it is important to quickly detect increases and decreases in its variability. In addition to preventing any increase in the variability of the process and any deterioration in the quality of the output, it is also important to search for special causes that may result in a smaller process dispersion. Considering this, users should always try to monitor for both increases and decreases in the variability. The process variability is commonly monitored by means of a Shewhart range chart. For small subgroup sizes this control chart has a lower control limit equal to zero. To help monitor for both increases and decreases in variability, Shewhart charts with probability limits or runs rules can be used. CUSUM and EWMA charts based on the range or a function of the subgroup variance can also be used. In this paper a CUSUM chart based on the subgroup range is proposed. Its performance is compared with that of other charts proposed in the literature. It is found that for small subgroup sizes, it has an excellent performance and it thus represents a powerful alternative to currently utilized strategies.
45 citations
TL;DR: In this article, the authors present a condition equivalent to the existence of a Riskless Shadow Asset that guarantees a minimum return when the asset prices are convex functions of interest rates or other state variables.
Abstract: This paper presents a condition equivalent to the existence of a Riskless Shadow Asset that guarantees a minimum return when the asset prices are convex functions of interest rates or other state variables. We apply this lemma to immunize default free and option free coupon bonds and reach three main conclusions. First, we give a solution to an old puzzle: why do simple duration matching portfolios work well in empirical studies of immunization even though they are derived in a model inconsistent with equilibrium and shifts on the term structure of interest rates are not parallel, as as sumed? Second, we establish a clear distinction between the concepts of immunized and maxmin portfolios. Third, we develop a framework that includes the main results of this literature as special cases. Next, we present a new strategy of immunization that consists in matching duration and minimizing a new linear dispersion measure of immunization risk. ” 1998 Elsevier Science B.V. All rights reserved.
42 citations
TL;DR: The authors provided new results concerning dynamics for a version of the Kiyotaki-Wright model (1989) in which strategies (either mixed or pure) are restricted so that agents play the same strategy for each opportunity set.
Abstract: I provide new results concerning dynamics for a version of the Kiyotaki-Wright model (1989) in which strategies (either mixed or pure) are restricted so that agents play the same strategy for each opportunity set. My results demonstrate the importance of examining stability in such models, because they show that many steady states focused on in the literature are not stable. Furthermore, I exhibit examples of two-period-convergent equilibria in which agents are indifferent among media of exchange. Consequently, their endogenous transaction pattern is analog to the coexistence of assets whose acceptability or “liquidity” varies inversely with their rates of return.
24 citations
TL;DR: In this article, the authors examined minimum advertised price (MAP), a vertical restraint that is observed in manufacturer-retailer interactions, and argued that MAP can be considered a combination of resale price maintenance (RPM) and a cooperative advertising subsidy.
Abstract: This paper examines minimum advertised price (MAP), a vertical restraint that is observed in manufacturer-retailer interactions. Under MAP, the manufacturer announces that it will reimburse retailers for a fraction of their advertising expenditures if retailers do not advertise the product at below a specified price. MAP can be considered a combination of resale price maintenance (RPM) and a cooperative advertising subsidy. Current antitrust law treats RPM as illegal per se, whereas MAP is judged according to a rule of reason. A framework is presented within with neither a minimum retail price nor a cooperative advertising subsidy is individually sufficient to enable maximization of profits in the complete manufacturer-retailer structure, but the two instruments together are. MAP is therefore a sufficient instrument for the maximization of joint profits. We argue that MAP can also be designed as a second-best instrument that replicates RPM.
23 citations
TL;DR: Preliminary results justify further investigation of the technique in this most difficult group of patients, as symptomatic changes correlated with the operative appearance, and with the subsequent changes in VLPP.
Abstract: The aim of the study was to asses the effectiveness of periurethral injection of autologous fat for the treatment of stress incontinence caused by inherent sphincter weakness in women following the repair of obstetric urogenital fistulae. Ten patients with symptomatic stress incontinence following repair of vesicovaginal or urethrovaginal fistula of obstetric origin were assessed clinically, by cystourethroscopy, and by Valsalva leak-point pressure (VLPP). Four showed some degree of bladder neck mobility and were treated by bladder neck suspension procedures. Six appeared to have pure sphincter weakness and were treated by periurethral injection of autologous fat. For logistic reasons, the initial follow-up was undertaken 2 weeks postoperatively, including clinical assessment and VLPP. Two patients were subjectively cured, 2 improved and 2 perceived no change in their symptoms following the procedure. The symptomatic changes correlated with the operative appearance, and with the subsequent changes in VLPP. Although numbers are small and follow-up short, we feel that these preliminary results justify further investigation of the technique in this most difficult group of patients.
Journal Article•
TL;DR: In this paper, the authors offer empirical evidence on the Mexican Federal Deputies' influence in the budget process and their lack of monitoring of public spending, showing that even if the Congress practically abdicated its powers in this respect during the time when the PRI was hegemonic, from the 1980's the legislature has exercised an ever growing budgetary influence.
Abstract: This note offers empirical evidence on the Mexican Federal Deputies' influence in the budget process and their lack of monitoring of public spending. Even if the Congress practically abdicated its powers in this respect during the time when the PRI was hegemonic, from the 1980's the legislature has exercised an ever growing budgetary influence. This process, however, has not implied an increased ex post oversight on spending. Once the PRI lost the absolute majority in the Chamber of Deputies, a new era in executive-legislative relations has begun in Mexico. From now on, financial resources will be negotiated between politicians coming from diverse political affiliations, and budgets will only be approved after a complex process of compromise and concession.
TL;DR: The use of artificial neural networks technology to build an automaton to assist neurologists during the differential diagnosis of AD and VD is explored and it is suggested that neurologists may improve their efficiency in getting a correct differential diagnosis and that some tests contribute little to the diagnosis.
Abstract: Differential diagnosis among different types of dementia, mainly between Alzheimer (AD) and Vascular Dementia (VD), offers great difficulties due to the overlapping among the symptoms, and signs presented by patients suffering these illnesses. A differential diagnosis of AD and VD can be obtained with a 100% of confidence through the analysis of brain tissue (i.e. a cerebral biopsy). This gold test involves an invasive technique, and thus it is rarely applied. Besides these difficulties, to get an efficient differential diagnosis of AD and VD is essential, because the therapeutic treatment needed by a patient differs depending on the illness he suffers. In this paper, we explore the use of artificial neural networks technology to build an automaton to assist neurologists during the differential diagnosis of AD and VD. First, different networks are analyzed in order to identify minimum sets of clinical tests, from those normally applied, that still allows a differential diagnosis of AD and VD; and, second, an artificial neural network is developed, using backpropagation and data based on these minimum sets, to assist physicians during the differential diagnosis of AD and VD. Our results allow us to suggest that, by using our neural network, neurologists may improve their efficiency in getting a correct differential diagnosis of AD and VD and, additionally, that some tests contribute little to the diagnosis, and that under some combinations they make it rather more difficult.
TL;DR: In this paper, the authors examined the impact of monetary redistribution policies on the amount of sunspot-induced volatility in an economy and showed that there is an efficiency cost of taxation: larger transfers lead to larger fluctuations in consumption.
TL;DR: In this paper, the authors consider the relationship between the real exchange rate and capital formation in a small open economy with two goods, one tradable and one not, and demonstrate that the real currency exchange rate must monotonically approach its steady state level.
Abstract: We consider the nature of the relationship between the real exchange rate and capital formation. We present a model of a small open economy that produces and consumes two goods, one tradable and one not. Domestic residents can borrow and lend abroad, and costly state verification (CSV) is a source of frictions in domestic credit markets. The real exchange rate matters for capital accumulation because it affects the␣potential for investors to provide internal finance, which mitigates the CSV problem. We demonstrate that the real exchange rate must monotonically approach its steady state level. However, capital accumulation need not be monotonic and real exchange rate appreciation can be associated with either a rising or a falling capital stock. The relationship between world financial market conditions and the real exchange rate is also investigated.
01 Jan 1998
TL;DR: In this paper, an alternative to such contracts is proposed when the full transfer of ownership rights to the infrastructure assets is not feasible, where income guarantees are used as incentive devices before demand and political risk to reward efficiency throughout project life span instead of serving as a means of indiscriminate compensation.
Abstract: In the late 1980s Mexico, like other emerging economies, embarked upon an accelerated expansion of its toll highway system by offering concessions to the private sector for construction and operation. The government awarded Build-Operate-Transfer (BOT) contracts where a private entity builds the infrastructure and operates it for a specific period. Then, in theory, once the private entity has recovered its investment and obtained a certain return, the infrastructure reverts to the public sector. This model has gained wide acceptance not only to roads but in water supply and power. However, agency cost in imperfectly competitive markets, like network industries, often led to opportunistic behavior by concessionaires. Income guarantees should be used as incentive devices before demand and political risk to reward efficiency throughout project life span instead of serving as a means of indiscriminate compensation. An alternative to such contracts is proposed when the full transfer of ownership rights to the infrastructure assets is not feasible.
Posted Content•
TL;DR: In this article, the authors take a game-theoretic approach to the analysis of juries by modeling voting as a game of incomplete information, allowing jurors to perceive a full spectrum of signals.
Abstract: We take a game-theoretic approach to the analysis of juries by modelling voting as a game of incomplete information. Rather than the usual assumption of two possible signals (one indicating guilt, the other innocence), we allow jurors to perceive a full spectrum of signals. Given any voting rule requiring a fixed fraction of votes to convict, we characterize the unique symmetric equilibrium of the game, and we consider the possibility of asymmetric equilibria: we give a condition under which no asymmetric equilibria exist and show that, without under which no asymmetric equilibria exist and show that, without it, asymmetric equilibria may exist. We offer a condition under which unanimity rule exhibits a bias toward convicting the innocent, regardless of the size of the jury, and we exhibit an example showing this bias can be reversed. And we prove a "jury theorem" for our general model: as the size of the jury increases, the probability of a mistaken judgment goes to zero for every voting rule, except unanimity rule; for unanimity rule, we give a condition under which the probability of a mistake is bounded strictly above zero, and we show that, without this condition, the probability of a mistake may go to zero.
TL;DR: The paper explains the limitations of the Partial Factors Design concept, such as applied in AISC and Eurocode, and outlines the fundamentals of the proposed Simulation-based Reliability Assessment method, SBRA, leading to a balanced reliability level and corresponding material savings.
01 Jan 1998
TL;DR: In this paper, the authors revisited the question of whether relative performance-adjusted contracts provide portfolio managers with adequate incentives to gather information and showed that when portfolio managers are constrained in their ability to short-sell, relative performance adjusted contracts can provide incentives for gathering more precise information.
Abstract: In this paper we revisit the question of whether relative performance-adjusted contracts provide portfolio managers with adequate incentives to gather information. We show that when portfolio managers are constrained in their ability to short-sell, relative performance-adjusted or linear ‘benchmarked’ contracts can provide incentives for gathering more precise information. We also provide conditions under which they emerge as optimal linear contracts contracts. We show that when borrowing constraints are present, the risk-averse manager’s optimal eort is, under certain conditions, an increasing function of her share on the portfolio’s return. In addition, the optimal contract oered by the risk-neutral client to the risk-neutral, short-selling constrained manager is shown to be a benchmarked contract for any value of the constraint. In the limit, as short-selling constraints are relaxed, the optimal contract is first-best.
01 Jan 1998
Abstract: The problem of making inferences about the ratio of two normal means has been addressed, both from the frequentist and Bayesian perspectives, by several authors. Most of this work is concerned with the homoscedastic case. In contrast, the situation where the variances are not equal has received little attention. Cox (1985) deals, within the frequentist framework, with a model where the variances are related to the means. His results are mainly based on Fieller's theorem whose drawbacks are well known. In this paper we present a Bayesian analysis of this model and discuss some related problems. An agronomical example is used throughout to illustrate the methods.
TL;DR: In this paper, a simple spatial model of executive-legislative policy-making in separation-of-power regimes is proposed, with deadlock as its dependent variable, and the model formalizes a set of necessary and sufficient conditions for deadlock.
Abstract: Executive-legislative deadlock is perceived as the Achilles’ heel of presidential democracy, because its occurrence has been associated with democratic breakdown in Latin America. Given the centrality of deadlock in the literature, I propose a simple spatial model of executive-legislative policy-making in separation-of-power regimes that takes deadlock as its dependent variable. The model formalizes a set of necessary and sufficient conditions for deadlock, filling a lacuna in the literature. It also addresses methodological difficulties in the empirical study of deadlock, and provide some initial evidence about vetoes in U.S. states to back-up some of the claims derived from the model.
TL;DR: In this article, minimum variance linear and unbiased estimators are provided for two different formulations of the problem, when a multivariate intervention analysis is carried out and an adjustment is needed to fulfill the restriction and when a univariate intervention was performed on the aggregate series obtained from the linear constraint, previous to the multivariate analysis, and the results of both analyses are required to be made compatible with each other.
Abstract: We consider the problem of estimating the effects of an intervention on a time series vector subjected to a linear constraint. Minimum variance linear and unbiased estimators are provided for two different formulations of the problem—(1) when a multivariate intervention analysis is carried out and an adjustment is needed to fulfill the restriction and (2) when a univariate intervention analysis was performed on the aggregate series obtained from the linear constraint, previous to the multivariate analysis, and the results of both analyses are required to be made compatible with each other. A banking example that motivated this work illustrates our solutions.
01 Jan 1998
TL;DR: For regular exponential families, Diaconis and Ylvisaker as mentioned in this paper showed that the posterior expectation of the mean parameter pi is linear in the canonical statistic, provided that a conjugate prior is used on the corresponding canonical parameter.
Abstract: For regular exponential families, Diaconis and Ylvisaker (1979) have shown that the posterior expectation of the mean parameter pi is linear in the canonical statistic, provided that a conjugate prior is used on the corresponding canonical parameter. In particular, the hyperparameters of the prior can be chosen so that this posterior expectation corresponds to an unbiased estimator of /i. In this paper we explore an analogue of this latter property for certain other parametrisations for which an unbiased estimator exists. The result is then used to find Bayes estimates under quadratic loss for such parametrisations. RESUMEN Estimadores Bayes para familias exponenciales Diaconis e Ylvisaker (1979) han demostrado que, en el caso de las familias exponenciales regulares, el valor esperado final del parametro medio ii es lineal como funcion de la estadistica canonica siempre y cuando se utilice una distribucion inicial conjugada realtiva al parametro canonico. En particular, los hiperparametros de esta distribucion pueden seleccionarse de manera que el valor esperado final de fi corresponda a un estimador insesgado. En este articulo se explora una propiedad analoga de ciertas parametrizaciones alternativas para las que existe un estimador insesgado. El resultado obtenido es usado entonces para encontrar estimadores de Bayes (bajo perdida cuadratica) para dichas parametrizaciones.
01 Jan 1998
15 Nov 1998
TL;DR: Vazquez et al. as discussed by the authors present the antologia de textos prepared by Esther Charabati and Gerardo Mendive, De la tolerancia a la convivencia solidaria, Mexico, 1995, paginas F-1 and F-17.
Abstract: 1. Tomo ambos casos de la antologia de textos preparada por Esther Charabati y Gerardo Mendive, De la tolerancia a la convivencia solidaria, Mexico, 1995, paginas F-1 y F-17. 2. Vease Taboada, Walter Beller, et al., Las costumbres juridicas de los indigenas en Mexico, Comision Nacional de Derechos Humanos, Mexico, 1994, pagina 90. Derechos de las minorias y tolerancia Rodolfo Vazquez * Para Fernando Salmeron In Memoriam
01 Jan 1998
TL;DR: PANRIK is a polynomial algorithm that efficiently solves for conjunctive goals by obtaining totally ordered object plans for each object of the problem domain and merging these partial plans into a partially ordered global plan that will become the solution to the problem.
Abstract: The article describes the design and behavior of PLANRIK, a domain independent hierarchical nonlinear planner that solves for interactive conjunctive goals in a simple, different and more efficient manner than other planners. PLANRIK is a polynomial algorithm that efficiently solves for conjunctive goals by obtaining totally ordered object plans for each object of the problem domain (i.e. a block in the blocks world, a ring in the towers of Hanoi, etc.), and by merging these partial plans into a partially ordered global plan that will become the solution to the problem. Each object plan is generated by ignoring all other objects, and by using a network of required object states resulting from previous planning activities within the solution process.