4,459 research outputs found
On the Inability of Markov Models to Capture Criticality in Human Mobility
We examine the non-Markovian nature of human mobility by exposing the
inability of Markov models to capture criticality in human mobility. In
particular, the assumed Markovian nature of mobility was used to establish a
theoretical upper bound on the predictability of human mobility (expressed as a
minimum error probability limit), based on temporally correlated entropy. Since
its inception, this bound has been widely used and empirically validated using
Markov chains. We show that recurrent-neural architectures can achieve
significantly higher predictability, surpassing this widely used upper bound.
In order to explain this anomaly, we shed light on several underlying
assumptions in previous research works that has resulted in this bias. By
evaluating the mobility predictability on real-world datasets, we show that
human mobility exhibits scale-invariant long-range correlations, bearing
similarity to a power-law decay. This is in contrast to the initial assumption
that human mobility follows an exponential decay. This assumption of
exponential decay coupled with Lempel-Ziv compression in computing Fano's
inequality has led to an inaccurate estimation of the predictability upper
bound. We show that this approach inflates the entropy, consequently lowering
the upper bound on human mobility predictability. We finally highlight that
this approach tends to overlook long-range correlations in human mobility. This
explains why recurrent-neural architectures that are designed to handle
long-range structural correlations surpass the previously computed upper bound
on mobility predictability
Labor Market Entry and Earnings Dynamics: Bayesian Inference Using Mixtures-of-Experts Markov Chain Clustering
This paper analyzes patterns in the earnings development of young labor market entrants over their life cycle. We identify four distinctly different types of transition patterns between discrete earnings states in a large administrative data set. Further, we investigate the effects of labor market conditions at the time of entry on the probability of belonging to each transition type. To estimate our statistical model we use a model-based clustering approach. The statistical challenge in our application comes from the di±culty in extending distance-based clustering approaches to the problem of identify groups of similar time series in a panel of discrete-valued time series. We use Markov chain clustering, proposed by Pamminger and Frühwirth-Schnatter (2010), which is an approach for clustering discrete-valued time series obtained by observing a categorical variable with several states. This method is based on finite mixtures of first-order time-homogeneous Markov chain models. In order to analyze group membership we present an extension to this approach by formulating a probabilistic model for the latent group indicators within the Bayesian classification rule using a multinomial logit model.Labor Market Entry Conditions, Transition Data, Markov Chain Monte Carlo, Multinomial Logit, Panel Data, Auxiliary Mixture Sampler, Bayesian Statistics
Sonification of probabilistic feedback through granular synthesis
We describe a method to improve user feedback, specifically the display of time-varying probabilistic information, through asynchronous granular synthesis. We have applied these techniques to challenging control problems as well as to the sonification of online probabilistic gesture recognition. We're using these displays in mobile, gestural interfaces where visual display is often impractical
Modeling, Predicting and Capturing Human Mobility
Realistic models of human mobility are critical for modern day applications, specifically for recommendation systems, resource planning and process optimization domains. Given the rapid proliferation of mobile devices equipped with Internet connectivity and GPS functionality today, aggregating large sums of individual geolocation data is feasible. The thesis focuses on methodologies to facilitate data-driven mobility modeling by drawing parallels between the inherent nature of mobility trajectories, statistical physics and information theory. On the applied side, the thesis contributions lie in leveraging the formulated mobility models to construct prediction workflows by adopting a privacy-by-design perspective. This enables end users to derive utility from location-based services while preserving their location privacy. Finally, the thesis presents several approaches to generate large-scale synthetic mobility datasets by applying machine learning approaches to facilitate experimental reproducibility
Homogenization of lateral diffusion on a random surface
We study the problem of lateral diffusion on a static, quasi-planar surface
generated by a stationary, ergodic random field possessing rapid small-scale
spatial fluctuations. The aim is to study the effective behaviour of a particle
undergoing Brownian motion on the surface viewed as a projection on the
underlying plane. By formulating the problem as a diffusion in a random medium,
we are able to use known results from the theory of stochastic homogenization
of SDEs to show that, in the limit of small scale fluctuations, the diffusion
process behaves quantitatively like a Brownian motion with constant diffusion
tensor . While will not have a closed-form expression in general, we are
able to derive variational bounds for the effective diffusion tensor, and using
a duality transformation argument, obtain a closed form expression for in
the special case where is isotropic. We also describe a numerical scheme
for approximating the effective diffusion tensor and illustrate this scheme
with two examples.Comment: 25 pages, 7 figure
Learning Periodic Human Behaviour Models from Sparse Data for Crowdsourcing Aid Delivery in Developing Countries
In many developing countries, half the population lives in rural locations,
where access to essentials such as school materials, mosquito nets, and medical
supplies is restricted. We propose an alternative method of distribution (to
standard road delivery) in which the existing mobility habits of a local
population are leveraged to deliver aid, which raises two technical challenges
in the areas optimisation and learning. For optimisation, a standard Markov
decision process applied to this problem is intractable, so we provide an exact
formulation that takes advantage of the periodicities in human location
behaviour. To learn such behaviour models from sparse data (i.e., cell tower
observations), we develop a Bayesian model of human mobility. Using real cell
tower data of the mobility behaviour of 50,000 individuals in Ivory Coast, we
find that our model outperforms the state of the art approaches in mobility
prediction by at least 25% (in held-out data likelihood). Furthermore, when
incorporating mobility prediction with our MDP approach, we find a 81.3%
reduction in total delivery time versus routine planning that minimises just
the number of participants in the solution path.Comment: Appears in Proceedings of the Twenty-Ninth Conference on Uncertainty
in Artificial Intelligence (UAI2013
Disposable Workforce in Italy
This paper explores the “disposable” patterns of workforce utilization in Italy. The term “disposable” reflects the fact that people enter the labor market, their services are “used” as a disposable commodity for few years, after which they leave the labor market and are no longer observable in the official data. Out of 100 new young entries, only 70 are still in the labor market 10 years after entry if their first job spell was at least one year long. For those – three times as many - whose first job is short (youth employment, unemployment, unemployment duration.
Disposable Workforce in Italy
This paper explores the "disposable" patterns of workforce utilization in Italy, well under way before the cyclical downturn of the early 90's and before the main reforms of the Italian labor market. The term "disposable" reflects the fact that many young people enter the labor market, their services are "used" as a disposable commodity for a few years, after which they leave the labor market altogether and are no longer observable in the official (administrative) data. Workforce disposal is evident and dramatic: out of 100 new young entries, about 70 are still in the labor market 10 years after entry if their first job spell was at least one year long. For those – three times as many – who have started their career with a short employment spell (youth employment, unemployment, unemployment duration
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