Estimation of Controlled Direct Effects in the Presence of Exposure-Induced Confounding and Latent Variables

Estimation of the direct effect of an exposure on an outcome requires adjustment for confounders of the exposure–outcome and mediator–outcome relationships. When some of the latter confounders have been affected by the exposure, then standard regression adjustment is prone to possibly severe bias. The use of inverse probability weighting under so-called marginal structural models has recently been suggested as a solution in the psychological literature. In this article, we show how progress can alternatively be made via G-estimation. We show that this estimation method can be easily embedded within the structural equation modeling framework and could in particular be used for estimating direct effects in the presence of latent variables. Moreover, by avoiding inverse probability weighting, it accommodates the typical problem of unstable weights in the alternative estimation approaches based on marginal structural models. We illustrate the approach both by simulations and by the analysis of a longitudinal study in individiduals who ended a romantic relationship. In this example we explore whether the effect of attachment anxiety during the relationship on mental distress 2 years after the breakup is mediated by rumination or not.     

马克思主义唯物论与教育技术装备工作

论述了用马克思主义唯物论来认识教育技术装备和如何在新形势下做好教育技术装备工作的关键问题.认为教育技术装备是教育活动的基本条件;是培养高素质人才的重要保证.为了做好教育技术装备工作,必须坚持"一个中心,两个重点"的工作思路;既要"跟踪教育",更要"开发教育";还要解放思想,用好市场.     

Self‐paced segmentation of written words on a touchscreen tablet promotes the oral production of nonverbal and minimally verbal children with autism

We investigated in a pilot study the effects of various types of visual mediation (photos, written words and self‐paced syllabic segmentation of written words displayed on a touchscreen tablet) that are thought to facilitate the oral production of nonverbal and minimally verbal children with autism, according to the participants’ level of oral language development and, more specifically, their ability to produce delayed echolalia. We also sought to identify the cognitive characteristics that need to be taken into account when seeking to develop the oral production of nonverbal children with autism. Results showed that the nonverbal and minimally verbal children with autism were able of using written words to produce them orally. Their performance was largely dependent on their level of language development. Tasks combining written and oral modalities prompted some of them to engage in oral production for the first time (isolated syllables for nonverbal children) and allowed others to produce non‐random strings of syllables (minimally verbal children).     

Probleme und Konzepte software-ergonomischer Beratung am Beispiel eines Informationssystems im World Wide Web (WWW)

Zusammenfassung. Die vorliegende Arbeit gibt Einblick in ein software- ergonomisches Beratungsprojekt zur Entwicklung eines internetbasierten Informationssystems. Sie beschreibt projektspezifische Probleme und die darauf aufbauende Konzeption des Beratungsprojekts. Es galt, insbesondere drei Problembereiche zu berücksichtigen: (1) Zusammenarbeit von Software-Entwicklern und Ergonomen, (2) Integration von Grundprinzipien software-ergonomischer Gestaltung in ein klassisches Vorgehensmodell der Software-Entwicklung (V-Modell) und (3) Wahl des Zeitpunkts für den Beginn der Beratung. Der konkrete Beratungsproze? unterteilte sich in drei Phasen: Analyse, Gestaltung und Bewertung des Informationssystems. In jeder dieser Phasen kamen verschiedene software-ergonomische Methoden (Schriftliche Benutzerbefragung, Gebrauchstauglichkeitsstudien etc.) zum Einsatz, die an die Bedingungen des Projektes angepa?t wurden. Der besondere Schwerpunkt lag dabei auf der Analysephase. Eingegangen am 23. November 1998 / Angenommen am 25. M?rz 1999     

Instrumental Variables Two-Stage Least Squares (2SLS) vs. Maximum Likelihood Structural Equation Modeling of Causal Effects in Linear Regression Models

In the presence of omitted variables or similar validity threats, regression estimates are biased. Unbiased estimates (the causal effects) can be obtained in large samples by fitting instead the Instrumental Variables Regression (IVR) model. The IVR model can be estimated using structural equation modeling (SEM) software or using Econometric estimators such as two-stage least squares (2SLS). We describe 2SLS using SEM terminology, and report a simulation study in which we generated data according to a regression model in the presence of omitted variables and fitted (a) a regression model using ordinary least squares, (b) an IVR model using maximum likelihood (ML) as implemented in SEM software, and (c) an IVR model using 2SLS. Coverage rates of the causal effect using regression methods are always unacceptably low (often 0). When using the IVR model, accurate coverage is obtained across all conditions when N = 500. Even when the IVR model is misspecified, better coverage than regression is generally obtained. Differences between 2SLS and ML are small and favor 2SLS in small samples (N ≤ 100).     

Consensus among stakeholders about success factors and indicators for quality of online and blended learning in adult education: a Delphi study

Quality models for online and blended learning (OBL) have mainly been developed in higher education. The literature indicates that these models are often conceptualised from the providers’ perspective. What is important for the quality of OBL from the students’ perspective has recently received increased attention in the literature. Consensus among stakeholders about students’ quality needs is useful to support dialogue between professionals to strategically adopt OBL and to ensure that the needs of students are met. This study aims to validate a quality instrument for OBL, taking a set of 74 quality indicators and analysing them in terms of seven success factors (credibility, accessibility, transparency, flexibility, interactivity, personalisation, productivity). The Delphi method was selected as most suited. Participants from adult education were asked to indicate on a 7-point Likert scale to what extent the indicators add to OBL quality to meet students’ needs. After four Delphi rounds, the participants agreed on definitions of success factors and 30 indicators. The results are useful for institutions, ministries of education and external quality assessment agencies to assess the quality of OBL and can support institutions to implement improvement actions to ensure that the needs of students are met.     

Mutual point-winning probabilities (MPW): a new performance measure for table tennis

ABSTRACT

We propose a new performance measure for table tennis players: the mutual point-winning probabilities (MPW) as server and receiver. The MPWs quantify a player’s chances to win a point against a given opponent, and hence nicely complement the classical match statistics history between two players. These new quantities are based on a Bradley-Terry-type statistical model taking into account the importance of individual points, since a rally at 8–2 in the first set is less crucial than a rally at the score of 9–9 in the final set. The MPWs hence reveal a player’s strength on his/her service against a given opponent as well as his/her capacity of scoring crucial points. We estimate the MPWs by means of maximum likelihood estimation and show via a Monte Carlo simulation study that our estimation procedure works well. In order to illustrate the MPWs’ versatile use, we have organized two round-robin tournaments of ten respectively eleven table tennis players from the Belgian table tennis federation. We compare the classical final ranking to the ranking based on MPWs, and we highlight how the MPWs shed new light on strengths and weaknesses of the players.     

Coplanar electrowetting-induced stirring as a tool to manipulate biological samples in lubricated digital microfluidics. Impact of ambient phase on drop internal flow pattern

Oscillating electrowetting on dielectrics (EWOD) with coplanar electrodes is investigated in this paper as a way to provide efficient stirring within a drop with biological content. A supporting model inspired from Ko et al. [Appl. Phys. Lett. 94, 194102 (2009)] is proposed allowing to interpret oscillating EWOD-induced drop internal flow as the result of a current streaming along the drop surface deformed by capillary waves. Current streaming behaves essentially as a surface flow generator and the momentum it sustains within the (viscous) drop is even more significant as the surface to volume ratio is small. With the circular electrode pair considered in this paper, oscillating EWOD sustains toroidal vortical flows when the experiments are conducted with aqueous drops in air as ambient phase. But when oil is used as ambient phase, it is demonstrated that the presence of an electrode gap is responsible for a change in drop shape: a pinch-off at the electrode gap yields a peanut-shaped drop and a symmetry break-up of the EWOD-induced flow pattern. Viscosity of oil is also responsible for promoting an efficient damping of the capillary waves which populate the surface of the actuated drop. As a result, the capillary network switches from one standing wave to two superimposed traveling waves of different mechanical energy, provided that actuation frequency is large enough, for instance, as large as the one commonly used in electrowetting applications (f ∼ 500 Hz and beyond). Special emphasis is put on stirring of biological samples. As a typical application, it is demonstrated how beads or cell clusters can be focused under flow either at mid-height of the drop or near the wetting plane, depending on how the nature of the capillary waves is (standing or traveling), and therefore, depending on the actuation frequency (150 Hz–1 KHz).     

From students to teachers: using surveys to build a culture of evidence and inquiry

In an effort to make decisions about teacher education policy and practice that were informed by research and evidence, participants in Boston College's ‘Teachers for a New Era’ Evidence Team (http://www.teachersforanewera.org) designed a portfolio of assessments and studies. This article describes one project in the portfolio – a series of surveys that trace teacher candidates' experiences over time and track shifts in these experiences as respondents progress from students during the pre‐service period to teachers in the first few years of work in the profession. The article illustrates how various constituencies in the teacher education programme and the larger university used survey data to guide practice, shape policies, and raise new questions about the curriculum, relationships with schools, and the performance of teachers and their pupils. The article argues that these surveys helped to create a new ‘culture of evidence and inquiry’ within which decisions about local policy and practice were made in the teacher preparation programme and the larger university.     

Use of Polarised Light Microscopy to Improve Conservation of Parchment

ABSTRACT

The preservation state of parchment primarily depends on the structure of the collagen fibre network, which in turn is responsible for optical anisotropy, i.e. birefringence. Polarised light microscopy can therefore be used as a non-invasive technique that allows recording of birefringence distribution in the parchment, which directly relates to stress–strain distribution. Using samples from diverse sources (commercial parchment, parchment used by restorers for book binding, and parchment fabricated for the purpose of this study), we assessed the capability of polarised light microscopy for various diagnostics. We performed, for instance, identification of gelatinised regions, layered or ?brous regions in parchment cross section, qualitative analysis of parchment fat content (lipids), observation of stress-induced patterns resulting from tensile tests, and observation of water diffusion. These proof-of-principle experiments extend the capability of polarised light microscopy far beyond its common use and open the path to its deployment in conservation studies.