Matching for Balance, Pairing for Heterogeneity in an Observational Study of the Effectiveness of For-Profit and Not-For-Profit High Schools in Chile

Conventionally, the construction of a pair-matched sample selects treated and control units and pairs them in a single step with a view to balancing observed covariates x and reducing the heterogeneity or dispersion of treated-minus-control response differences, Y. In contrast, the method of cardinality matching developed here first selects the maximum number of units subject to covariate balance constraints and, with a balanced sample for x in hand, then separately pairs the units to minimize heterogeneity in Y. Reduced heterogeneity of pair differences in responses Y is known to reduce sensitivity to unmeasured biases, so one might hope that cardinality matching would succeed at both tasks, balancing x, stabilizing Y. We use cardinality matching in an observational study of the effectiveness of for-profit and not-for-profit private high schools in Chile—a controversial subject in Chile—focusing on students who were in government run primary schools in 2004 but then switched to private high schools. By pairing to minimize heterogeneity in a cardinality match that has balanced covariates, a meaningful reduction in sensitivity to unmeasured biases is obtained

First principles quasiparticle damping rates in bulk lead

First principles calculations of the damping rates (inverse inelastic lifetimes) of low energy quasiparticles in bulk Pb are presented. Damping rates are obtained both for excited electrons and holes with energies up to 8 eV on a set of k vectors throughout the Brillouin zone (BZ). Strong localization effects in the calculated lifetimes are found. Averaged over the BZ inelastic lifetimes versus quasiparticle energy are reported as well. In addition, the effect of the spin-orbit induced splitting in the band structure on the calculated lifetimes in Pb is investigated.Comment: 10 pages, 8 figures, 5 table

Effect of protocol-related variables and women's characteristics on the cumulative false-positive risk in breast cancer screening

Background: Reducing the false-positive risk in breast cancer screening is important. We examined how the screening-protocol and women's characteristics affect the cumulative false-positive risk. Methods: This is a retrospective cohort study of 1 565 364 women aged 45-69 years who underwent 4 739 498 screening mammograms from 1990 to 2006. Multilevel discrete hazard models were used to estimate the cumulative false-positive risk over 10 sequential mammograms under different risk scenarios. Results: The factors affecting the false-positive risk for any procedure and for invasive procedures were double mammogram reading [odds ratio (OR) = 2.06 and 4.44, respectively], two mammographic views (OR = 0.77 and 1.56, respectively), digital mammography (OR = 0.83 for invasive procedures), premenopausal status (OR = 1.31 and 1.22, respectively), use of hormone replacement therapy (OR = 1.03 and 0.84, respectively), previous invasive procedures (OR = 1.52 and 2.00, respectively), and a familial history of breast cancer (OR = 1.18 and 1.21, respectively). The cumulative false-positive risk for women who started screening at age 50-51 was 20.39% [95% confidence interval (CI) 20.02-20.76], ranging from 51.43% to 7.47% in the highest and lowest risk profiles, respectively. The cumulative risk for invasive procedures was 1.76% (95% CI 1.66-1.87), ranging from 12.02% to 1.58%. Conclusions: The cumulative false-positive risk varied widely depending on the factors studied. These findings are relevant to provide women with accurate information and to improve the effectiveness of screening programs

Enhancement of tribological behavior of rolling bearings by applying a multilayer ZrN/ZrCN coating

This paper focuses on the tribological behaviour of ZrN/ZrCN coating on bearing steel substrates DIN 17230, 100Cr6/1.3505. Coatings are applied at room temperature processes by means of Cathodic Arc Evaporation (CAE), a kind of Physical Vapor Deposition (PVD) technique. In order to achieve a satisfactory compromise between coating-substrate adhesion and the surface roughness requirement of the bearing rings, a polish post-processing is proposed. Different polish post-processing times and conditions are applied. The coated and polished bearing rings are tested under real friction torque test protocols. These tests show that the application of the coating does not entail a significant improvement in friction performance of the bearing. However, fatigue tests in real test bench are pending to evaluate the possible improvement in bearing life time

Cancer screening in Spain

Objective: To describe the current status of breast, colorectal and cervical cancer screening in Spain. Methodology: The situation was analysed on the basis of data drawn from surveys conducted in each autonomous region (Comunidad Autónoma). Results: Currently, breast cancer screening coverage is 100%. In 2007, overall participation was 67.0% with an adherence of 91.2%. The detection rate was 3.4 per thousand, 15.1% intraductal and 30% invasive <1 cm in diameter, with 65% showing axilary node negative. Colorectal cancer screening had been implemented in six regions (4.5% of the target population). Participation ranged from 17.2% to 42.3%, with positive test percentages ranging from 1.7 per thousand (guaiac) to 9.5% (immunological). The invasive cancer detection rate was 1.7 per thousand (guaiac) and 3.4 per thousand (immunological). In most cases, cervical cancer screening was undertaken opportunistically, with an estimated coverage of 69.0%. Conclusions: In Spain, cancer screening is being conducted in accordance with national and international recommendations. The fact that screening programmes are operated as a network has led to a high degree of consensus as to the methodology and information systems to be used to enable joint evaluation

Exchange interaction and its tuning in magnetic binary chalcogenides

Using a first-principles Green's function approach we study magnetic properties of the magnetic binary chalcogenides Bi2Te3, Bi2Se3, and Sb2Te3. The magnetic coupling between transition-metal impurities is long-range, extends beyond a quintuple layer, and decreases with increasing number of d electrons per 3d atom. We find two main mechanisms for the magnetic interaction in these materials: the indirect exchange interaction mediated by free carriers and the indirect interaction between magnetic moments via chalcogen atoms. The calculated Curie temperatures of these systems are in good agreement with available experimental data. Our results provide deep insight into magnetic interactions in magnetic binary chalcogenides and open a way to design new materials for promising applications

L1 transfer in the acquisition of manner and path in Spanish by native speakers of English

In this article the authors argue that L1 transfer from English is not only important in the early stages of L2 acquisition of Spanish, but remains influential in later stages if there is not enough positive evidence for the learners to progress in their development (Lefebvre, White, & Jourdan, 2006). The findings are based on analyses of path and manner of movement in stories told by British students of Spanish (N = 68) of three different proficiency levels. Verbs that conflate motion and path, on the one hand, are mastered early, possibly because the existence of Latinate path verbs, such as enter and ascend in English, facilitate their early acquisition by British learners of Spanish. Contrary to the findings of Cadierno (2004) and Cadierno and Ruiz (2006), the encoding of manner, in particular in boundary crossing contexts, seems to pose enormous difficulties, even among students who had been abroad on a placement in a Spanish-speaking country prior to the data collection. An analysis of the frequency of manner verbs in Spanish corpora shows that one of the key reasons why students struggle with manner is that manner verbs are so infrequent in Spanish. The authors claim that scarce positive evidence in the language exposed to and little or no negative evidence are responsible for the long-lasting effect of transfer on the expression of manner