Set Of Available Instruments Research Articles

HIGHER-ORDER APPROXIMATION OF IV ESTIMATORS WITH INVALID INSTRUMENTS

This paper analyzes the higher-order approximation of instrumental variable (IV) estimators in a linear homoskedastic IV regression model when a large set of instruments with potential invalidity is present. We establish theoretical results on the higher-order mean-squared error (MSE) approximation of the two-stage least-squares (2SLS), the limited information maximum likelihood (LIML), the Fuller (FULL), the bias-adjusted 2SLS, and jackknife version of the LIML and FULL estimators by allowing for local violations of the instrument exogeneity conditions. Based on the approximation to the higher-order MSE, we consider the instrument selection criteria that can be used to choose among the set of available instruments. We demonstrate the asymptotic optimality of the instrument selection procedure proposed by Donald and Newey (2001, Econometrica 69, 1161–1191) in the presence of locally (faster than $N^{-1/2}$ ) invalid instruments in the sense that the dominant term in the MSE with the chosen instrument is asymptotically equivalent to the infeasible optimum. Furthermore, we propose instrument selection procedures to choose instruments among the sets of conservative (known) valid instruments and potentially locally ( $N^{-1/2}$ ) invalid instruments based on the higher-order MSE of the IV estimators by considering the bias-variance trade-off.

Validação do Youth Quality of Life Instrument (YQOL-R) para a população portuguesa

Objetivo: É incontornável o estatuto que o conceito de qualidade de vida assume hoje na prática e políticas de saúde pública. Na infância e adolescência é ainda escassa a investigação, tornando-se crucial o desenvolvimento de instrumentos de qualidade vida relacionada com a saúde validados para esta população. O presente trabalho tem como objetivo fundamental analisar as qualidades psicométricas e validar a versão portuguesa do Youth Quality of Life (YQOL-R). Métodos: A amostra é constituída por 507 adolescentes, com idades compreendidas entre os 12 e os 19 anos (M = 15,74; DP = 1,62), a frequentar o 3.º ciclo do ensino básico e ensino secundário de escolas públicas do ensino regular. Para além do citado instrumento a validar, os jovens preencheram também, para a análise da validade convergente e divergente, o Kidscreen-27 e a Escala da Depressão, Ansiedade e Stresse (EADS-21). Resultados: O YQOL-R apresenta uma estrutura fatorial de quatro fatores, semelhantes à versão original americana (individual, relações sociais, ambiente e qualidade de vida em geral). Possui uma boa consistência interna e uma adequada estabilidade temporal. Mostrou correlações significativas e no sentido esperado com as variáveis em estudo. Foram igualmente encontradas diferenças entre sexos em relação à qualidade de vida, sendo os rapazes a reportarem em média níveis mais elevados de perceção da qualidade de vida, comparativamente às raparigas. Conclusões: Futuros estudos devem ser realizados em amostras clínicas para confirmação dos dados. Não obstante esta limitação, o presente estudo contribuiu para a disponibilização de um novo instrumento para avaliação da qualidade de vida em crianças e adolescentes, o qual evidenciou boas propriedade psicométricas, apoiando, assim empiricamente, a sua utilização nas práticas de saúde e investigação em amostras da comunidade.

Validation of the Youth Quality of Life Instrument for Portuguese Adolescents

Introduction Quality of Life (QoL) plays a remarkable role in practice and public health policy. However, research on QoL among children and adolescents is still scarce and it seems crucial to develop and validate assessment tools for measuring health-related QoL. Objectives The current study aims to analyse the psychometric properties and validate the Portuguese version of the Youth Quality of Life Instrument (YQOL-R; Patrick et al., 2002). In addition, the convergent and divergent validities are examined with related constructs. Methods Participants were 507 adolescents, with ages between 12 and 19 years old, attending middle and high schools. Together with YQOL-R, participants also filled out the Kidscreen-27 (Gaspar & Matos, 2008) and the Depression Anxiety and Stress Scales (Pais-Ribeiro, Honrado & Leal, 2004). Results The Portuguese version of YQOL-R showed a four-factor structure (dimensions: Self, Relationships, Environment, General Quality of Life), similar to the original version. This instrument also revealed a good internal reliability and adequate temporal stability. YQOL-R showed positive correlations with health-related quality of life and negative associations with depression, anxiety and stress symptoms. There were significant gender differences regarding quality of life, with boys reporting higher levels of perceived quality of life than girls. Conclusions Future studies should be conducted to ensure these findings among clinical samples or physical conditions. Nevertheless, this study contributes to the set of available instruments for the assessment of QoL among children and adolescents, suggesting that the YQOL-R may be a useful tool for research and health practices in community samples.

Estimation of Distribution Algorithms: Applications to the Design of Process Sensor Networks

The optimal location of sensors involves the selection of type, number and location of sensorsfrom a set of available instruments with certain values of cost, precision and reliability. Theoptimal design not only satisfies economic criteria, but also some requirements on the qualityof key variable estimates. In this work, a methodology for solving the sensor network designproblem based on Estimation of Distribution Algorithms is presented. These algorithms areincluded in the Evolutionary Computation paradigm and substitute the probability distributionestimation of a population composed by potential solutions and its subsequent sampling forthe use of the classic crossover and mutation operators. The performance of the new strategyis evaluated and compared with that provided by other evolutionary techniques for the case ofa steam metering network of a methanol synthesis plant.

Unexploited Gains from International Diversification

Using unique micro data on U.S. institutional investor portfolios, this paper studies how capital, meant to be invested globally, is actually diversified internationally. We show that although the mutual fund industry has moved toward funds that have more flexibility to invest across countries and regions (global funds), mutual funds invest in a finite, rather small number of firms, almost independently of the set of available instruments. The number of mutual fund holdings in stocks and countries from a given region declines as funds become more global. This restricted investment practice has a cost: there are unexploited gains from international diversification. Mutual funds could achieve better returns by broadening their investment scope to include stocks held by specialized funds within the same mutual fund family. This investment pattern is neither explained by the lack of available instruments or information, nor by a better ability of global funds to minimize losses.