policy relevant treatment effects accounting for individual level heterogeneity in the response to treatment is a major development in the econometric literature on program evaluation a substantial body of empirical evidence demonstrates that econometric models fit on individual level data manifest heterogeneity in treatment effects that is present even after conditioning on observables an important distinction is the one between evaluation models where participation in the program being evaluated is based at least in part on unobserved idiosyncratic responses to treatment and models where participation is not based on unobserved idiosyncratic responses this is the distinction between selection on unobservables and selection on observables the validity of entire classes of evaluation estimators hinges on whether or not they allow agents to act on unobserved idiosyncratic responses in a wide variety of applications the available evidence suggests that not only are ex post postenrollment responses heterogeneous but that ex ante decisions to participate in programs are based in part on these heterogeneous responses heckman and vytlacil 2000b 2001

nonparametric estimation of sample selection models sample selection models provide an important way of accounting for economic decisions that combine discrete and continuous choices and of correcting for nonrandom sampling nonparametric estimators for these models are developed in this paper these can be used for estimating shapes and important economic quantities as in standard nonparametnc regression endogeneity of regressors of interest is allowed for series estimators for these models are developed which are useful for imposing additivity restnctions that arise from selection corrections convergence rates and asymptotic normality results are derived an application to returns to schooling among australian young females is given

selection investment and women s relative wages over time in theory growing wage inequality within gender should cause women to invest more in their market productivity and should differentially pull able women into the workforce our paper uses heckman s two step estimator and identification at infinity on repeated current population survey cross sections to calculate relative wage series for women since 1970 that hold constant the composition of skills we find that selection into the female full time full year workforce shifted from negative in the 1970s to positive in the 1990s and that the majority of the apparent narrowing of the gender wage gap reflects changes in female workforce composition we find the same types of composition changes by measuring husbands wages and national longitudinal survey iq data as proxies for unobserved skills our findings help to explain why growing wage equality between genders coincided with growing inequality within gender

micro data heterogeneity and the evaluation of public policy nobel lecture this paper summarizes the contributions of microeconometrics to economic knowledge four main themes are developed 1 microeconometricians developed new tools to respond to econometric problems raised by the analysis of the new sources of micro data produced after the second world war 2 microeconometrics improved on aggregate time series methods by building models that linked economic models for individuals to data on individual behavior 3 an important empirical regularity detected by the field is the diversity and heterogeneity of behavior this heterogeneity has profound consequences for economic theory and for econometric practice 4 microeconometrics has contributed substantially to the scientific evaluation of public policy

the estimation of wage gains and welfare gains in self selection models the authors modify the basic self sele ction model for the effects ofeducation training unions and other activities on wages by including heterogeneity of rewards to the activity i e diffe rences across individuals in the rate of return to the activity the authors sho w that such heterogeneity creates a new form of selectionbias they provide tes ts for its presence and draw out its implications for the wage and welfare gains to the activity an empirical application provides strong support for such hete rogeneityin one particular training program copyright 1987 by mit press

does early child care affect children s development we study how early child care ecc affects children s development in a marginal treatment effect framework that allows for rich forms of observed and unobserved effect heterogeneity exploiting a reform in germany that induced school districts to expand ecc at different points in time we find strong but diverging effects on children s motor and socio emotional skills children who were most likely to attend ecc benefit in terms of their motor skill development children who were least likely to attend ecc gain in terms of their socio emotional skill development especially boys and children from disadvantaged families such as those with low education or migration backgrounds simulating expansions of ecc we find that a moderate expansion fosters motor skills for all children and language skills for boys and immigrant children a progressive expansion of ecc improves all children s socio emotional development but neither their motor skills nor their language skills

advanced pricing in electrical systems i theory this paper sets forth a comprehensive theory for the real time pricing of electricity that includes selected ancillary services and extends the theory to incorporate constraints on power quality and environment impact that often influence the operation of a power system this paper is part i of a two paper set it sets forth the mathematical development of the extended model for real time pricing the formulation is novel in that it combines the dynamic equations for load frequency control with the static equations of a constrained optimal power flow part ii derives optimal nodal specific real time prices for both real and reactive power the prices derived include additive premia or opportunity costs reflecting the effects of voltage regulation maintenance of generation and transmission reserves regulation of frequency and tie line flows removal and or control of power harmonics and others

on using linear regressions in welfare economics this article consists of two parts the first part shows that the ordinary least squares regression coefficient is a weighted average of slopes between adjacent sample points when applied to a linear regression with income as the independent variable the regression coefficient depends heavily on the slopes of high income groups the weight of the highest income decile may well exceed that of the other nine deciles this may be undesirable especially if the regression is used for welfare analysis because the marginal propensities to consume attributed to the commodities are determined by the high income groups the second part of the article proposes alternative estimators the extended gini estimators that enable investigators to control the weighting scheme and to incorporate their social views into the weighting scheme of the estimators

why understanding smoking bans is important for estimating their effects california s restaurant smoking bans and restaurant sales i introduction a voluminous literature has sought to quantify the effect of smoking bans typically on the quantity of smoking but also on the performance of affected businesses 1 various time periods have been explored types of bans considered locales examined and specifications employed nonetheless the majority of studies share two common failings first smoking bans of a given type e g a restaurant ban are treated as homogenous when in fact such bans have been enacted at various jurisdictional levels municipality county or state at various times in various orders and in various combinations with other types of smoking bans and with similar bans at other jurisdictional levels second empirical specifications do not adequately control for preexisting trends in the dependent variable as a result many studies arrive at fundamentally wrong conclusions we illustrate these points in an investigation of how california s restaurant smoking bans have affected restaurant sales we analyze the effect of smoking bans on restaurant sales for two reasons first the issue plays a role in the policy debate more than 150 studies many published in refereed journals and others in consulting reports undertaken for municipalities have explored whether smoking bans help or hinder restaurants scollo and lal 2005 yet few of these studies properly account for the effects of preexisting trends or changes in trends for the closely related question of ban endogeneity or for ban heterogeneity second restaurant sales data are very rich well measured available by municipality by quarter and over an extended period therefore we can identify effects that would be obscured by cruder data e g periodic survey responses enabling us to draw lessons applicable to studies of the effect of other types of smoking bans e g workplace bans in other dimensions e g smoking prevalence we investigate 267 california municipalities for which the california state board of equalization provides quarterly taxable restaurant sales 2 we begin by employing naive specifications which treat bans as homogenous and control simplistically for trends representative of those typically estimated in the literature the results of our naive specifications indicate that smoking bans have a large negative effect on restaurant revenues however when we examine municipal and state bans separately we find a positive association between municipal bans and restaurant sales and a negative association between the state ban and restaurant sales finally when we control properly for preexisting trends in the dependent variable we find no substantial evidence of any causal relationship running from either municipal bans or the state ban to restaurant sales thus we reach two main conclusions the first is that california s municipal restaurant smoking bans are endogenous in a critical way restaurant sales growth or something correlated with restaurant sales growth appears to cause restaurant bans not vice versa the second is that because communities are heterogenous one must analyze the effect of a ban taking into account the level at which the ban was enacted pooling data and treating smoking bans as homogenous as many studies do is inappropriate cities that impose bans on themselves are likely to differ systematically from those that have bans forced on them by a higher jurisdiction county or state relatedly analyzing and or instrumenting for smoking bans using state level data again as many studies do may fail to capture the relevant variation when the bans have force at a lower level of jurisdiction e g a municipal ban our analysis although focused on restaurant bans and sales has implications for the more extensive literature on how smoking bans influence smoking behavior most importantly it demonstrates the crucial nature of identifying and controlling for trends in the dependent variable whether restaurant revenue as in our data set or smoking rates

r d and subsidies at the firm level an application of parametric and semi parametric two step selection models this paper analyzes the effects of public r d subsidies on r d expenditure in the german manufacturing sector the focus is on the question whether public r d funding stimulates or crowds out private investment cross sectional data at the firm level is used by apllying parametric and semiparametric selection models it turns out that public funding increases firms r d expenditure altough the magnitude of the treatment effect depends on the assumpions imposed by the particular selection model

the interpretation of instrumental variables estimators in simultaneous equations models with an application to the demand for fish in markets where prices are determined by the intersection of supply and demand curves standard identification results require the presence of instruments that shift one curve but not the other these results are typically presented in the context of linear models with fixed coefficients and additive residuals the first contribution of this paper is an investigation of the consequences of relaxing both the linearity and the additivity assumption for the interpretation of linear instrumental variables estimators without these assumptions the standard linear instrumental variables estimator identifies a weighted average of the derivative of the behavioural relationship of interest a second contribution is the formulation of critical identifying assumptions in terms of demand and supply at different prices and instruments rather than in terms of functional form specific residuals our approach to the simultaneous equations problem and the average derivative interpretation of instrumental variables estimates is illustrated by estimating the demand for fresh whiting at the fulton fish market strong and credible instruments for identification of this demand function are available in the form of weather conditions at sea

measuring benefits from a marketing cooperative in the copper river fishery the degradation of product quality is one form of rent dissipation resulting from incomplete property rights in fisheries industry structure and information asymmetries can also lead to underinvestment in product quality even when property rights are well defined in this article we empirically examine whether the voluntary formation of a marketing cooperative was able to mitigate market failures that led to the production of inferior quality fish specifically we use a difference in differences estimation strategy to measure the impact that the copper river fishermen s cooperative an alaskan salmon marketing cooperative had on ex vessel salmon prices and salmon quality measures we find that the cooperative was able to improve product quality as well as attract and sustain a higher price for its salmon our findings provide empirical support for many of the key tenets of cooperative theory specifically we find evidence that marketing cooperatives can address existing market failures that marketing cooperatives can have advantages in high quality product markets and that over time as a result of their success marketing cooperatives may lead to lasting producer benefits even though they become obsolete due to nonmember free riding

the effect of male migration on employment patterns of women in nepal what is the impact of male migration on the labor market behavior of women in nepal the instrumental variable full information maximum likelihood method is applied to data from the 2004 nepal household survey to account for unobserved factors that could simultaneously affect men s decision to migrate and women s decision to participate in the labor market the results indicate that male migration has a negative impact on the level of the labor market participation by women in the migrant sending household there is evidence of substantial heterogeneity based on both observable and unobservable characteristics in the impact of male migration the findings highlight the important gender dimension of the impact of predominantly male migration on the well being of sending households strategies for economic development in nepal should take into account such gender aspects of the migration dynamics

determinants of health care decisions insurance utilization and expenditures abstract this paper studies three interrelated health care decisions insurance utilization and expenditures the model treats insurance as an endogenous variable with respect to both utilization and expenditures addresses potential selection issues and takes into account that the decisions to use health care and the level of treatment are determined by different decision makers we employ semiparametric methods to avoid making distributional assumptions using the medical expenditure panel survey 2005 data the semiparametric approach predicts insurance to increase the level of expenditures by 48 a number in accord with an important experimental study and less than half that obtained using parametric methods

gender wage inequality during sri lanka s post reform growth a distributional analysis abstract this paper investigates gender wage inequality in sri lanka during 1992 2014 a period of robust economic growth following pro market reforms the gap in mean wages between men and women decreased steadily over this period unconditional quantile regression reveals the decline in gender wage inequality was driven by the upper half of the distribution and was due to improvements in women s observable human capital yet the pay structure became more unequal indicating widening gender gaps in the returns to labor market characteristics and in unobservable determinants of wages the gender gap in pay structure widened disproportionately in the lower half of the distribution coinciding with falling absolute and relative returns to women in manufacturing industries and production occupations facing greater international competition the study also demonstrates selection bias underestimates the gender wage gap and overestimates the gains in equality over time factors that hinder gender equality in the labor market are discussed along with policy implications

price knowledge in household demand for utility services a household s decision to acquire price knowledge is endogenous in the demand for utility services and may affect elasticities and consumption levels a simultaneous equation model with endogenous switching is developed to evaluate the effects of price knowledge and other sources of heterogeneity results indicate informed households were more responsive to average and marginal price signals informed households also use less water but this is due to heterogeneity rather than price knowledge controlling for heterogeneity price knowledge actually increases monthly water usage the implications of accounting for differences in price knowledge in utility demand modeling and demand management policy are discussed

eliciting and utilizing willingness to pay evidence from field trials in northern ghana we utilize the becker degroot marschak 1964 mechanism to estimate the willingness to pay for clean drinking water technology in northern ghana the bdm mechanism has attractive properties for empirical research allowing us to directly estimate demand compute heterogeneous treatment effects and study the screening and causal effects of prices with minor modifications to a standard field experiment setting we demonstrate the implementation of bdm along these three dimensions compare it to the standard take it or leave it method for eliciting willingness to pay and discuss practical issues for implementing the mechanism in true field settings jel classifications c93 d12 d82 l11 l31

a security constrained bid clearing system for the new zealand wholesale electricity market this paper reports upon the mathematical models and implementation of the scheduling pricing and dispatch spd application for the new zealand electricity market nzem spd analyzes bids for energy offers reserve offers and energy demands and recognizes explicitly the effects on bid clearing due to transmission congestion network losses reserve requirements and ramp rate limits advanced lp solution methods are utilized to solve the large scale constrained optimization problem results on a 67 bus test system and the nzem are included

estimating engel curves under unit and item nonresponse summary this paper estimates food engel curves using data from the first wave of the survey on health aging and retirement in europe share our statistical model simultaneously takes into account selectivity due to unit and item nonresponse endogeneity problems and issues related to flexible specification of the relationship of interest we estimate both parametric and semiparametric specifications of the model the parametric specification assumes that the unobservables in the model follow a multivariate gaussian distribution while the semiparametric specification avoids distributional assumptions about the unobservables copyright 2011 john wiley sons ltd

parametric and semiparametric estimation of sample selection models an empirical application to the female labour force in portugal this paper applies both parametric and semiparametric methods to the estimation of wage and participation equations for married women in portugal the semiparametric estimators considered are the two stage estimators proposed by newey 1991 and andrews and schafgans 1998 the selection equation results are compared using the specification tests proposed by horowitz 1993 horowitz and hardle 1994 and the wage equation results are compared using a hausman test significant differences between the two approaches indicate the inappropriateness of the standard parametric methods to the estimation of the model and for the purpose of policy simulations the greater departure seems to occur in the range of the low values of the index corresponding to a specific group of women copyright 2001 john wiley sons ltd

estimating marginal returns to education this paper estimates marginal returns to college for individuals induced to enroll in college by different marginal policy changes the recent instrumental variables literature seeks to estimate this parameter but in general it does so only under strong assumptions that are tested and found wanting we show how to utilize economic theory and local instrumental variables estimators to estimate the effect of marginal policy changes our empirical analysis shows that returns are higher for individuals with values of unobservables that make them more likely to attend college we contrast our estimates with iv estimates of the return to schooling

alternative approaches to evaluation in empirical microeconomics four alternative but related approaches to empirical evaluation of policy interventions are studied social experiments natural experiments matching methods and instrumental variables in each case the necessary assumptions and the data requirements are considered for estimation of a number of key parameters of interest these key parameters include the average treatment effect the treatment on the treated and the local average treatment effect some issues of implementation and interpretation are discussed drawing on the labour market programme evaluation literature

inversion of real time spot prices in the direction of real power flow in a transmission line an increasing number of electricity markets employing some form of spot pricing however limited experience of the behavior of spot prices exists this paper introduces and investigates one particular aspect of pricing behavior observed in the new zealand spot market known as price inversion spot prices are generally calculated using some form of opf or power flow software the phenomena of price inversion is investigated using the dc power flow implemented in the new zealand spot market and using a full ac power flow price inversion is shown to be dependent on the physical characteristics of the power system the economic implications of price inversion are also discussed

site selection bias in program evaluation site selection bias can occur when the probability that a program is adopted or evaluated is correlated with its impacts i test for site selection bias in the context of the opower energy conservation programs using 111 randomized control trials involving 8 6 million households across the united states predictions based on rich microdata from the first 10 replications substantially overstate efficacy in the next 101 sites several mechanisms caused this positive selection for example utilities in more environmentalist areas are more likely to adopt the program and their customers are more responsive to the treatment also because utilities initially target treatment at higher usage consumer subpopulations efficacy drops as the program is later expanded the results illustrate how program evaluations can still give systematically biased out of sample predictions even after many replications jel codes c93 d12 l94 o12 q41

evaluating public programs with close substitutes the case of head start this paper empirically evaluates the cost effectiveness of head start the largest early childhood education program in the united states using data from the randomized head start impact study hsis we show that head start draws a substantial share of its participants from competing preschool programs that receive public funds this both attenuates measured experimental impacts on test scores and reduces the program s net social costs a cost benefit analysis demonstrates that accounting for the public savings associated with reduced enrollment in other subsidized preschools can reverse negative assessments of the program s social rate of return estimates from a semi parametric selection model indicate that head start is about as effective at raising test scores as competing preschools and that its impacts are greater on children from families unlikely to participate in the program efforts to expand head start to new populations are therefore likely to boost the program s social rate of return provided that the proposed technology for increasing enrollment is not too costly

semiparametric estimation of the intercept of a sample selection model this paper provides a consistent and asymptotically normal estimator for the intercept of a semiparametrically estimated sample selection model the estimator uses a decreasingly small fraction of all observations as the sample size goes to infinity as in heckman 1990 in the semiparametrics literature estimation of the intercept has typically been subsumed in the nonparametric sample selection bias correction term the estimation of the intercept however is important from an economic perspective for instance it permits one to determine the wage gap between unionized and nonunionized workers decompose the wage differential between different socioeconomic groups e g male female and black white and evaluate the net benefits of a social programme

changes in the distribution of male and female wages accounting for employment composition using bounds this paper examines changes in the distribution of wages using bounds to allow for the impact of nonrandom selection into work we show that worst case bounds can be informative however because employment rates in the united kingdom are often low they are not informative about changes in educational or gender wage differentials thus we explore ways to tighten these bounds using restrictions motivated from economic theory with these assumptions we find convincing evidence of an increase in inequality within education groups changes in educational differentials and increases in the relative wages of women

semiparametric three step estimation methods for simultaneous equation systems this paper proposes a new method for estimating a structural model of labour supply in which hours of work depend on log wages and the wage rate is considered endogenous the main innovation with respect to other related estimation procedures is that a nonparametric additive structure in the hours of work equation is permitted though the focus of the paper is on this particular application a three step methodology for estimating models in the presence of the above econometric problems is described in the first step the reduced form parameters of the participation equation are estimated by a maximum likelihood procedure adapted for estimation of an additive nonparametric function in the second step the structural parameters of the wage equation are estimated after obtaining the selection corrected conditional mean function finally in the third step the structural parameters of the labour supply equation are estimated using local maximum likelihood estimation techniques the paper concludes with an application to illustrate the feasibility performance and possible gain of using this method copyright 2005 john wiley sons ltd

who participates in r d subsidy programs the case of spanish manufacturing firms abstract empirical evidence on the effectiveness of r d subsidies to firms has produced mixed results so far one possible explanation is that firms and project selection rules may be quite heterogeneous both across agencies and across industries leading to different outcomes in terms of the induced additional private effort here we focus on the participation stage using a sample of spanish firms we test for differences across agencies and industries our results suggest that firms in the same industry face different hurdles to participate in different agencies programs that participation patterns may reflect a combination of agency goals and that patterns differ across high tech and low tech industries

gender wage differences in malaysia parametric and semiparametric estimation this paper is an empirical study on the labor force in peninsular malaysia parametric and semiparametric estimated wage equations which correct for sample selection bias are used to assess the returns to education and extent of gender discrimination to estimate in the semiparametric case the wage equation intercept which is needed for the oaxaca wage decomposition consistently we apply the newly developed andrews schafgans andrews d w k schafgans m m a 1998 semiparametric estimation of the intercept of a sample selection model review of economic studies 65 497 518 estimator the results suggest that discrimination favoring men in malaysia is still quite prevalent while for malays the sons of the soil the strong level of discrimination favoring malay men is negated by the semiparametric estimation results

applying the copula approach to sample selection modelling the limited availability of tractable multivariate distributions undermines the validity of the standard parametric approach to sample selection modelling copula distributions can be very useful in situations where the applied researcher has a prior on the distributional form of the margins since the modelling of the latter is separated from that of the dependence structure the present article first presents an application to female work data afterwards the approach is analysed in an application to contingent valuation data on recreational values of forests it is shown that the copula approach is especially beneficial in case of strong departures from the hypothesis of normality

market structure and multiple equilibria in airline markets we provide a practical method to estimate the payoff functions of players in complete information static discrete games with respect to the empirical literature on entry games originated by bresnahan and reiss 1990 and berry 1992 the main novelty of our framework is to allow for general forms of heterogeneity across players without making equilibrium selection assumptions we allow the effects that the entry of each individual airline has on the profits of its competitors its competitive effects to differ across airlines the identified features of the model are sets of parameters partial identification such that the choice probabilities predicted by the econometric model are consistent with the empirical choice probabilities estimated from the data we apply this methodology to investigate the empirical importance of firm heterogeneity as a determinant of market structure in the u s airline industry we find evidence of heterogeneity across airlines in their profit functions the competitive effects of large airlines american delta united are different from those of low cost carriers and southwest also the competitive effect of an airline is increasing in its airport presence which is an important measure of observable heterogeneity in the airline industry then we develop a policy experiment to estimate the effect of repealing the wright amendment on competition in markets out of the dallas airports we find that repealing thewright amendment would increase the number of markets served out of dallas love

the impacts of family size on investment in child quality using multiple births as an exogenous shift in family size i investigate the impact of the number of children on child investment and child well being using data from the 1980 us census five percent public use micro sample 2sls results demonstrate that parents facing a change in family size reallocate resources in a way consistent with becker s quantity quality model a larger family generated by twins in a later birth reduces the likelihood that older children attend private school reduces the mother s labor force participation and increases the likelihood that parents divorce the impact of family size on a measure of child outcome such as grade retention is less clear the results indicate that for both measures of child investment and child well being the 2sls estimates are statistically distinguishable from ols estimates indicating an omitted variables bias in the single equation model

semiparametric estimation of consumer demand systems with micro data maximum likelihood and two step estimators of censored demand systems yield biased and inconsistent parameter estimates when the assumed joint distribution of disturbances is incorrect this paper proposes a semiparametric estimator that retains the computational advantage of the two step approach but is immune to distributional misspecification the key difference between the proposed estimator and the two step estimator is that the parameters of the binary censoring equations are estimated using a distribution free single index model we implement the proposed estimator using household level data obtained from the hainan province in china specification test lends support to our approach

on the decomposition of wage differentials the often used method for decomposing wage differentials into human capital and discrimination components is reformulated so that both t he disadvantage or cost discrimination it imposes on a black or minority wage earner and the advantage or benefit it bestows on a white or majority wage earner can be estimated copyright 1988 by mit press

evaluating marginal policy changes and the average effect of treatment for individuals at the margin this paper develops methods for evaluating marginal policy changes we characterize how the effects of marginal policy changes depend on the direction of the policy change and show that marginal policy effects are fundamentally easier to identify and to estimate than conventional treatment parameters we develop the connection between marginal policy effects and the average effect of treatment for persons on the margin of indifference between participation in treatment and nonparticipation and use this connection to analyze both parameters we apply our analysis to estimate the effect of marginal changes in tuition on the return to going to college

a simple adjustment for bandwidth snooping kernel based estimators such as local polynomial estimators in regression discontinuity designs are often evaluated at multiple bandwidths as a form of sensitivity analysis however if in the reported results a researcher selects the bandwidth based on this analysis the associated confidence intervals cis may not have correct coverage even if the estimator is unbiased this article proposes a simple adjustment that gives correct coverage in such situations replace the normal quantile with a critical value that depends only on the kernel and ratio of the maximum and minimum bandwidths the researcher has entertained we tabulate these critical values and quantify the loss in coverage for conventional cis for a range of relevant cases a conventional 95 ci has coverage between 70 and 90 and our adjustment amounts to replacing the conventional critical value 1 96 with a number between 2 2 and 2 8 our results also apply to other settings involving trimmed data such as trimming to ensure overlap in treatment effect estimation we illustrate our approach with three empirical applications

the toll of fertility on mothers wellbeing using multiple births as source of variation we study the impact of fertility on the overall wellbeing of mothers first using us census data for the year 1980 we study the impact of number of children on family arrangements welfare participation and poverty status second using the national health interview survey nhis for the period 1982 2003 we study the impact on a series of health risk factors the findings reveal first that an increase in family size increases the likelihood of marital breakdown second we find evidence that mothers facing an increase in family size are not only more likely to live with other family members such as grandparents aunts and uncles they are also more likely to receive help from welfare programs third consistent with an increase in welfare participation families mothers are more likely to fall below the poverty line and they face a reduction in total family income the results using nhis confirm a negative impact of fertility on marriage stability and an increase in welfare participation measured by the likelihood of using medicaid and for some samples a reduction in the take up of private health insurance finally we find evidence that a shock in fertility increases the likelihood of mothers suffering from high blood pressure and becoming obese

opf for reactive pricing studies on the ngc system retail transmission services like those being provided by the national grid company ngc in england and wales pose new challenges for the pricing of reactive power supply a reactive power market approach has been proposed by ngc and continues to be evaluated such an approach includes a novel requirement for transmission constrained economic dispatch of var a problem in the security constrained optimal power flow opf class the problem formulations handled by the opf package in use could not accommodate ngc s requirements this paper describes the reactive pricing problem being addressed the modeling requirements and the resulting extensions made to the opf formulation and package it discusses the test results obtained to date on the ngc system

training wages and sample selection estimating sharp bounds on treatment effects this paper empirically assesses the wage effects of the job corps program one of the largest federally funded job training programs in the u s even with the aid of a randomized experiment the impact of a training program on wages is difficult to study because of sample selection a pervasive problem in applied microeconometric research wage rates are only observed for those who are employed and employment status itself may be affected by the training program this paper develops an intuitive trimming procedure for bounding average treatment effects in the presence of sample selection in contrast to existing methods the procedure requires neither exclusion restrictions nor a bounded support for the outcome of interest identification results estimators and their asymptotic distribution are presented the bounds suggest that the program raised wages consistent with the notion that the job corps raises earnings by increasing human capital rather than solely through encouraging work the estimator is generally applicable to typical treatment evaluation problems in which there is nonrandom sample selection attrition copyright wiley blackwell