778 research outputs found
Forestiera ligustrina (Michx.) Poir.
https://thekeep.eiu.edu/herbarium_specimens_byname/21085/thumbnail.jp
Estimating Heterogeneous Consumer Preferences for Restaurants and Travel Time Using Mobile Location Data
This paper analyzes consumer choices over lunchtime restaurants using data
from a sample of several thousand anonymous mobile phone users in the San
Francisco Bay Area. The data is used to identify users' approximate typical
morning location, as well as their choices of lunchtime restaurants. We build a
model where restaurants have latent characteristics (whose distribution may
depend on restaurant observables, such as star ratings, food category, and
price range), each user has preferences for these latent characteristics, and
these preferences are heterogeneous across users. Similarly, each item has
latent characteristics that describe users' willingness to travel to the
restaurant, and each user has individual-specific preferences for those latent
characteristics. Thus, both users' willingness to travel and their base utility
for each restaurant vary across user-restaurant pairs. We use a Bayesian
approach to estimation. To make the estimation computationally feasible, we
rely on variational inference to approximate the posterior distribution, as
well as stochastic gradient descent as a computational approach. Our model
performs better than more standard competing models such as multinomial logit
and nested logit models, in part due to the personalization of the estimates.
We analyze how consumers re-allocate their demand after a restaurant closes to
nearby restaurants versus more distant restaurants with similar
characteristics, and we compare our predictions to actual outcomes. Finally, we
show how the model can be used to analyze counterfactual questions such as what
type of restaurant would attract the most consumers in a given location.Marie Curie Fellowship from the European Commission (H2020 programme, grant agreement 706760)
Diagnosis of lung cancer â improving survival rates
Lung cancer is a major global health burden with high incidence rates but poor long-term survival. Currently, the majority of cases are diagnosed at an advanced stage when surgical resection is not feasible. Screening for lung cancer has been a major focus of research for the last 40 years. Despite this, there is still a lack of evidence to promote its use outside clinical trials. More recently, interest has focused on promoting earlier recognition of symptomatic disease among both the general public and primary care physicians in order to encourage more timely investigation and referral to secondary care. The hope is that this approach may increase the proportion of disease identified in the early tages, allowing more surgical resections and improved five-year survival rates. This article provides an overview of the current evidence base in terms of early diagnosis of lung cancer and provides some examples of innovations to promote this
Federated Causal Inference in Heterogeneous Observational Data
We are interested in estimating the effect of a treatment applied to
individuals at multiple sites, where data is stored locally for each site. Due
to privacy constraints, individual-level data cannot be shared across sites;
the sites may also have heterogeneous populations and treatment assignment
mechanisms. Motivated by these considerations, we develop federated methods to
draw inference on the average treatment effects of combined data across sites.
Our methods first compute summary statistics locally using propensity scores
and then aggregate these statistics across sites to obtain point and variance
estimators of average treatment effects. We show that these estimators are
consistent and asymptotically normal. To achieve these asymptotic properties,
we find that the aggregation schemes need to account for the heterogeneity in
treatment assignments and in outcomes across sites. We demonstrate the validity
of our federated methods through a comparative study of two large medical
claims databases
Preserving Derivative Information while Transforming Neuronal Curves
The international neuroscience community is building the first comprehensive
atlases of brain cell types to understand how the brain functions from a higher
resolution, and more integrated perspective than ever before. In order to build
these atlases, subsets of neurons (e.g. serotonergic neurons, prefrontal
cortical neurons etc.) are traced in individual brain samples by placing points
along dendrites and axons. Then, the traces are mapped to common coordinate
systems by transforming the positions of their points, which neglects how the
transformation bends the line segments in between. In this work, we apply the
theory of jets to describe how to preserve derivatives of neuron traces up to
any order. We provide a framework to compute possible error introduced by
standard mapping methods, which involves the Jacobian of the mapping
transformation. We show how our first order method improves mapping accuracy in
both simulated and real neuron traces under random diffeomorphisms. Our method
is freely available in our open-source Python package brainlit
The signalling effect of eco-labels in modern coastal tourism
As the demand for environmentally sustainable tourism grows, eco-labels are becoming increasingly popular as a signal of environmental quality. However, the existence of a causal link between awarding a seaside eco-label and the increase in tourism flows is still under discussion in the literature. In this article, we gauge the signalling impact of a specific eco-label, the Blue Flag award, using detailed data on tourism flows to seaside Italian destinations during the period 2008-2012. We adopt a recent econometric modelling strategy - the synthetic control method - in shaping estimation results and testing the sensitivity and robustness of our results. We find that being awarded the Blue Flag increases the flow of domestic tourists for up to three seasons after assignment. However, we find no effect for the flow of international tourists. Investigating the mechanisms driving the results, we find that the award of a Blue Flag only positively affects the flow of domestic tourists when it is used as a driver of organisation, coordination and integrated management of the tourism supply
Ground-layer wavefront reconstruction from multiple natural guide stars
Observational tests of ground layer wavefront recovery have been made in open
loop using a constellation of four natural guide stars at the 1.55 m Kuiper
telescope in Arizona. Such tests explore the effectiveness of wide-field seeing
improvement by correction of low-lying atmospheric turbulence with ground-layer
adaptive optics (GLAO). The wavefronts from the four stars were measured
simultaneously on a Shack-Hartmann wavefront sensor (WFS). The WFS placed a 5 x
5 array of square subapertures across the pupil of the telescope, allowing for
wavefront reconstruction up to the fifth radial Zernike order. We find that the
wavefront aberration in each star can be roughly halved by subtracting the
average of the wavefronts from the other three stars. Wavefront correction on
this basis leads to a reduction in width of the seeing-limited stellar image by
up to a factor of 3, with image sharpening effective from the visible to near
infrared wavelengths over a field of at least 2 arc minutes. We conclude that
GLAO correction will be a valuable tool that can increase resolution and
spectrographic throughput across a broad range of seeing-limited observations.Comment: 25 pages, 8 figures, to be published in Astrophys.
Leeway for the loyal: a model of employee discretion
This article examines the factors underlying task discretion from an economist's perspective. It argues that the key axis for understanding discretion is the trade-off between the positive effects of discretion on potential output per employee and the negative effects of greater leeway on work effort. In empirical analysis using matched employer-employee data, it is shown that discretion is strongly affected by the level of employee commitment. In addition, discretion is generally greater in high-skilled jobs, although not without exceptions, and lower where employees are under-skilled. Homeworking and flexitime policies raise employee discretion. The impact of teamworking is mixed. In about half of cases team members do not jointly decide about work matters, and the net effect of teams on task discretion in these cases is negative. In other cases, where team members do decide matters jointly, the impact is found to be neutral according to employees' perceptions, or positive according to managers' perceptions. There are also significant and substantial unobserved establishment-level factors which affect task discretion
Risk factors for delay in symptomatic presentation: a survey of cancer patients
Background: Delay in symptomatic presentation leading to advanced stage at diagnosis may contribute to poor cancer survival. To inform public health approaches to promoting early symptomatic presentation, we aimed to identify risk factors for delay in presentation across several cancers.
Methods: We surveyed 2371 patients with 15 cancers about nature and duration of symptoms using a postal questionnaire. We calculated relative risks for delay in presentation (time from symptom onset to first presentation >3 months) by cancer, symptoms leading to diagnosis and reasons for putting off going to the doctor, controlling for age, sex and deprivation group.
Results: Among 1999 cancer patients reporting symptoms, 21% delayed presentation for >3 months. Delay was associated with greater socioeconomic deprivation but not age or sex. Patients with prostate (44%) and rectal cancer (37%) were most likely to delay and patients with breast cancer least likely to delay (8%). Urinary difficulties, change of bowel habit, systemic symptoms (fatigue, weight loss and loss of appetite) and skin symptoms were all common and associated with delay. Overall, patients with bleeding symptoms were no more likely to delay presentation than patients who did not have bleeding symptoms. However, within the group of patients with bleeding symptoms, there were significant differences in risk of delay by source of bleeding: 35% of patients with rectal bleeding delayed presentation, but only 9% of patients with urinary bleeding. A lump was a common symptom but not associated with delay in presentation. Twenty-eight percent had not recognised their symptoms as serious and this was associated with a doubling in risk of delay. Embarrassment, worry about what the doctor might find, being too busy to go to the doctor and worry about wasting the doctorâs time were also strong risk factors for delay, but were much less commonly reported (<6%).
Interpretation: Approaches to promote early presentation should aim to increase awareness of the significance of cancer symptoms and should be designed to work for people of the lowest socioeconomic status. In particular, awareness that rectal bleeding is a possible symptom of cancer should be raised
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