On model selection and model misspecification in causal inference

Standard variable selection procedures, primarily developed for the construction of outcome prediction models, are routinely applied when assessing exposure effects in observational studies. We argue that this tradition is sub-optimal and prone to yield bias in exposure effect estimators as well as their corresponding uncertainty estimators. We weigh the pros and cons of confounder-selection procedures and propose a procedure directly targeting the quality of the exposure effect estimator. We further demonstrate that certain strategies for inferring causal effects have the desirable features (a) of producing (approximately) valid confidence intervals, even when the confounder-selection process is ignored, and (b) of being robust against certain forms of misspecification of the association of confounders with both exposure and outcome.     

Requantization transcoding for H.264/AVC video coding

In this paper, efficient solutions for requantization transcoding in H.264/AVC are presented. By requantizing residual coefficients in the bitstream, different error components can appear in the transcoded video stream. Firstly, a requantization error is present due to successive quantization in encoder and transcoder. In addition to the requantization error, the loss of information caused by coarser quantization will propagate due to dependencies in the bitstream. Because of the use of intra prediction and motion-compensated prediction in H.264/AVC, both spatial and temporal drift propagation arise in transcoded H.264/AVC video streams. The spatial drift in intra-predicted blocks results from mismatches in the surrounding prediction pixels as a consequence of requantization. In this paper, both spatial and temporal drift components are analyzed. As is shown, spatial drift has a determining impact on the visual quality of transcoded video streams in H.264/AVC. In particular, this type of drift results in serious distortion and disturbing artifacts in the transcoded video stream. In order to avoid the spatially propagating distortion, we introduce transcoding architectures based on spatial compensation techniques. By combining the individual temporal and spatial compensation approaches and applying different techniques based on the picture and/or macroblock type, overall architectures are obtained that provide a trade-off between computational complexity and rate-distortion performance. The complexity of the presented architectures is significantly reduced when compared to cascaded decoder–encoder solutions, which are typically used for H.264/AVC transcoding. The reduction in complexity is particularly large for the solution which uses spatial compensation only. When compared to traditional solutions without spatial compensation, both visual and objective quality results are highly improved.     

Road safety in a globalised and more sustainable world: Current issues and future challenges

Although many countries have had considerable success in reducing traffic injuries over recent decades, there are still some fundamental problems in this area. At the same time, there is increasing focus on road safety research and policy development in the context of globalisation, sustainability, liveability and health. This special section presents a selection of papers that were presented at the annual ICTCT workshop held on the 8th and 9th of November 2012 in Hasselt, Belgium, and accepted for publication in Accident Analysis and Prevention following the journal's reviewing procedure. The aim of the ICTCT workshop was to analyse road safety facts, data and visions for the future in the wider context of current issues and future challenges in road safety.     

Supervised ranking in the weka environment

Software for solving the supervised ranking problem is presented. Four variants of the Ordinal Stochastic Dominance Learner (OSDL) are given, together with the space and time complexity of their implementations. It is shown that the described software, which includes two further algorithms for supervised ranking, fits seamlessly into the weka environment.     

Organizing the Web's Information Explosion to Discover Unknown Unknowns

This paper introduces the TORISHIKI-KAI project, which aims to construct a million-word-scale semantic network from the Web using state of the art knowledge acquisition methods. The resulting network can be browsed as a Web search directory, and we show that the directory is useful for finding “unknown unknowns” — in the infamous words of D.H. Rumsfeld: things “we don't know we don't know.” Because typically we have no way to look for information we don't even know is missing, a crucial characteristic of unknown unknowns is that they are very difficult to discover through keyword-based Web search. Some examples of the unknown unknowns we have found include unexpected troubles associated with commercial products, surprising new combinations of ingredients in new recipes, unexpected tools or methods for commiting suicide, and so on. We expect such information to be useful for risk management, innovation support, and the detection of harmful information on the Web.     

Instantaneous,Simple, and Reversible Revealing of Invisible Patterns Encrypted in Robust Hollow Sphere Colloidal Photonic Crystals

The colors of photonic crystals are based on their periodic crystalline structure. They show clear advantages over conventional chromophores for many applications, mainly due to their anti‐photobleaching and responsiveness to stimuli. More specifically, combining colloidal photonic crystals and invisible patterns is important in steganography and watermarking for anticounterfeiting applications. Here a convenient way to imprint robust invisible patterns in colloidal crystals of hollow silica spheres is presented. While these patterns remain invisible under static environmental humidity, even up to near 100% relative humidity, they are unveiled immediately (≈100 ms) and fully reversibly by dynamic humid flow, e.g., human breath. They reveal themselves due to the extreme wettability of the patterned (etched) regions, as confirmed by contact angle measurements. The liquid surface tension threshold to induce wetting (revealing the imprinted invisible images) is evaluated by thermodynamic predictions and subsequently verified by exposure to various vapors with different surface tension. The color of the patterned regions is furthermore independently tuned by vapors with different refractive indices. Such a system can play a key role in applications such as anticounterfeiting, identification, and vapor sensing.     

A semi-automatic annotation tool for unobtrusive gesture analysis

In a variety of research fields, including linguistics, human–computer interaction research, psychology, sociology and behavioral studies, there is a growing interest in the role of gestural behavior related to speech and other modalities. The analysis of multimodal communication requires high-quality video data and detailed annotation of the different semiotic resources under scrutiny. In the majority of cases, the annotation of hand position, hand motion, gesture type, etc. is done manually, which is a time-consuming enterprise requiring multiple annotators and substantial resources. In this paper we present a semi-automatic alternative, in which the focus lies on minimizing the manual workload while guaranteeing highly accurate annotations. First, we discuss our approach, which consists of several processing steps such as identifying the hands in images, calculating motion of the hands, segmenting the recording in gesture and non-gesture events, etc. Second, we validate our approach against existing corpora in terms of accuracy and usefulness. The proposed approach is designed to provide annotations according to the McNeill (Hand and mind: what gestures reveal about thought, University of Chicago Press, Chicago, 1992) gesture space and the output is compatible with annotation tools such as ELAN or ANVIL.     

Inferring comprehensible business/ICT alignment rules

We inferred business rules for business/ICT alignment by applying a novel rule induction algorithm on a data set containing rich alignment information polled from 641 organisations in 7 European countries. The alignment rule set was created using AntMiner+, a rule induction technique with a reputation of inducing accurate, comprehensible, and intuitive predictive models from data. Our data set consisted of 18 alignment practices distilled from an analysis of relevant publications and validated by a Delphi panel of experts. The goal of our study was to describe practical guidelines for managers in obtaining better alignment of ICT investments with business requirements. Our obtained rule set showed the multi-disciplinary nature of B/ICT alignment. We discuss implication of the alignment rules for practitioners.     

Relationship between pupillary size,brightness, and photoreceptor responses for unrelated self-luminous stimuli at low photopic light levels

Research on the correlation between the initial pupillary light reflex, the perceptual brightness, and the excitations of the photoreceptors was performed for unrelated self-luminous 10° stimuli at low photopic light levels (5 to 80 cd/m²). All stimuli were optically characterized using a spectroradiometer. For determining the pupillary diameter, an Eye Tracker was used. The perceived brightness was evaluated with the magnitude estimation method. Test stimuli were presented alternating with a reference stimulus and the Michelson contrast of the pupillary diameter between test and reference conditions was calculated. Six observers (three female and three male) participated, with ages between 30 and 39 years (with an average of 34.5 years). It was found that the coefficient of determination between the pupillary response and the perceived stimulus brightness was higher than the corresponding value for luminance, allowing the suggestion that brightness has a greater effect on pupillary size than luminance. Nevertheless, this is not the complete story: highly saturated red and blue stimuli both induce a high brightness perception but the pupil contraction induced by the blue stimuli is much greater than for the red stimuli. Pupillary diameter was also studied as a function of the relative excitations of the five photoreceptors. The effect of rod and ipRGC excitations on pupillary size variation seems to be larger than that of the other photoreceptors. However, for the working conditions prevailing in this research, it could be expected that rods are not very active and that the ipRGC response might be the major driving mechanism.