Edge-disjoint double rays in infinite graphs: a Halin type result

We show that any graph that contains k edge-disjoint double rays for any k>0 contains also infinitely many edge-disjoint double rays. This was conjectured by Andreae in 1981.Comment: 15 pages, 2 figure

Decision trees in epidemiological research

Background: In many studies, it is of interest to identify population subgroups that are relatively homogeneous with respect to an outcome. The nature of these subgroups can provide insight into effect mechanisms and suggest targets for tailored interventions. However, identifying relevant subgroups can be challenging with standard statistical methods. Main text: We review the literature on decision trees, a family of techniques for partitioning the population, on the basis of covariates, into distinct subgroups who share similar values of an outcome variable. We compare two decision tree methods, the popular Classification and Regression tree (CART) technique and the newer Conditional Inference tree (CTree) technique, assessing their performance in a simulation study and using data from the Box Lunch Study, a randomized controlled trial of a portion size intervention. Both CART and CTree identify homogeneous population subgroups and offer improved prediction accuracy relative to regression-based approaches when subgroups are truly present in the data. An important distinction between CART and CTree is that the latter uses a formal statistical hypothesis testing framework in building decision trees, which simplifies the process of identifying and interpreting the final tree model. We also introduce a novel way to visualize the subgroups defined by decision trees. Our novel graphical visualization provides a more scientifically meaningful characterization of the subgroups identified by decision trees. Conclusions: Decision trees are a useful tool for identifying homogeneous subgroups defined by combinations of individual characteristics. While all decision tree techniques generate subgroups, we advocate the use of the newer CTree technique due to its simplicity and ease of interpretation

Off-Policy Evaluation for Large Action Spaces via Policy Convolution

Developing accurate off-policy estimators is crucial for both evaluating and optimizing for new policies. The main challenge in off-policy estimation is the distribution shift between the logging policy that generates data and the target policy that we aim to evaluate. Typically, techniques for correcting distribution shift involve some form of importance sampling. This approach results in unbiased value estimation but often comes with the trade-off of high variance, even in the simpler case of one-step contextual bandits. Furthermore, importance sampling relies on the common support assumption, which becomes impractical when the action space is large. To address these challenges, we introduce the Policy Convolution (PC) family of estimators. These methods leverage latent structure within actions -- made available through action embeddings -- to strategically convolve the logging and target policies. This convolution introduces a unique bias-variance trade-off, which can be controlled by adjusting the amount of convolution. Our experiments on synthetic and benchmark datasets demonstrate remarkable mean squared error (MSE) improvements when using PC, especially when either the action space or policy mismatch becomes large, with gains of up to 5 - 6 orders of magnitude over existing estimators.Comment: Under review. 36 pages, 31 figure

Facial Mobility and Recovery in Patients with Unilateral Facial Paralysis

Objective: (a) To quantify longitudinal 3D changes in facial soft tissue movements in adults with unilateral facial paralysis, and (b) to compare the patients’ movements with an age- and sex-frequency matched control group. Settings and Sample Population: Prospective 3D facial movement data of 36 patients and 68 control participants. Patients’ data were collected within 6 weeks of onset of symptoms (baseline) and then at 3 and 12 weeks after baseline. Materials and Methods: The 3D facial movement data were collected during different facial animations. Mean group measurements of displacement, velocity and asymmetry were computed. Two sample t tests were used to test for significant group differences, and linear mixed models were fit to test for significant changes over time in the patient group. Also, 3D dynamic modelling and vector plots were computed to isolate the patients’ abnormal movements and/or paralysis. Results: The patients’ mean baseline movements were significantly less for both the paralysed and contralateral sides of the face with much greater movement asymmetry than the controls. Patients’ mean measures improved significantly from baseline to 12 weeks. The measures were closer to, but fell short of, the control values. Conclusion: In unilateral facial paralysis, the contralateral facial side was affected by the paralysis and may be tethered or limited in its movement by the paralysed side. The comprehensive measurement set and 3D facial mapping effectively tracked patient recovery and isolated paralysed facial regions. The 3D measures can be used for diagnosis and outcome assessment of different treatments.</p

Smartphones and Social Health: Does Reduced Phone Use Lead to Better Social Health Outcomes?

Within the past decade, smartphones have become a necessity for modern life. However, there has been little to no experimental scientific research on how problematic use of these devices influences social health. Problematic smartphone use (PSU) may reduce our ability to communicate and understand one another, thereby reducing our ability to bond together, connect, and improve relationships. Research has examined many social health correlates of PSU, including technology’s impact on emotional intelligence, relationship satisfaction, and loneliness. However, these studies have been limited in causal validity by their survey-based approach. We propose the use of a pre-test/post-test experiment designed to reduce PSU in the treatment group to explore whether reducing PSU improves social health over time. We plan to help people reduce their phone use through an educational intervention over five weeks while tracking and analyzing their smartphone usage over that time. During these five weeks, we will measure social health indicators including emotional intelligence, empathy, social sensitivity, social anxiety, and loneliness

A modelling approach to assess the impact of climate change & anthropogenic activity on the water resources of the Narmada river basin

The Narmada river basin is a highly regulated & artificially influenced catchment in Peninsular India, covering 98 796 km2. The basin includes the states of Madhya Pradesh, Maharashtra & Gujarat, supporting a population of over 16 million people. Agriculture is the dominant land use within the basin, accounting for over 56% of the basin area. There are over 3000 interventions, with up to another 30 dams planned for construction over the next half-century. The study of the Narmada basin is part of an ongoing collaboration between CEH (UK) & NIH (India) with the goal of increasing water security for those living within the basin & surrounding watersheds

Student Voices Session / Moderator: Ed Vermue

Hear how objects-based pedagogy has shaped and positively impacted the educational experiences of students. Jennifer Lin: English and East Asian StudiesUna Creedon-Carey: Medieval StudiesSarah Rose Lejeune: Book ArtsJulian Hirsch: ArchaeologyNathan Carpenter: Africatown Projec

State and Development: The Need for a Reappraisal of the Current Literature

This essay tries to bring out some of the complexities that are overlooked in the usual treatment of the state in the institutional economics literature and supplement the latter with a discussion of some alternative approaches to looking at the possible developmental role of the state. It refers to a broader range of development goals (including the structural transformation of the economy) and focuses on problems like the resolution of coordination failures and collective-action problems, the conflicting issues of commitment and accountability and the need for balancing the trade-offs they generate, some ingredients of state capacity and political coalition building usually missed in the literature, the possible importance of rent sharing in a political equilibrium, the advantages and problems of political centralization and decentralization, and the multidimensionality of state functions that may not be addressed by markets or private firms