Laws of the single logarithm for delayed sums of random fields

We extend a law of the single logarithm for delayed sums by Lai to delayed sums of random fields. A law for subsequences, which also includes the one-dimensional case, is obtained in passing.Comment: Published in at http://dx.doi.org/10.3150/07-BEJ103 the Bernoulli (http://isi.cbs.nl/bernoulli/) by the International Statistical Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm

Sharing Means Renting?: An Entire-marketplace Analysis of Airbnb

Airbnb, an online marketplace for accommodations, has experienced a staggering growth accompanied by intense debates and scattered regulations around the world. Current discourses, however, are largely focused on opinions rather than empirical evidences. Here, we aim to bridge this gap by presenting the first large-scale measurement study on Airbnb, using a crawled data set containing 2.3 million listings, 1.3 million hosts, and 19.3 million reviews. We measure several key characteristics at the heart of the ongoing debate and the sharing economy. Among others, we find that Airbnb has reached a global yet heterogeneous coverage. The majority of its listings across many countries are entire homes, suggesting that Airbnb is actually more like a rental marketplace rather than a spare-room sharing platform. Analysis on star-ratings reveals that there is a bias toward positive ratings, amplified by a bias toward using positive words in reviews. The extent of such bias is greater than Yelp reviews, which were already shown to exhibit a positive bias. We investigate a key issue---commercial hosts who own multiple listings on Airbnb---repeatedly discussed in the current debate. We find that their existence is prevalent, they are early-movers towards joining Airbnb, and their listings are disproportionately entire homes and located in the US. Our work advances the current understanding of how Airbnb is being used and may serve as an independent and empirical reference to inform the debate.Comment: WebSci '1

Applicability of the user engagement scale to mobile health : a survey-based quantitative study

Background: There has recently been exponential growth in the development and use of health apps on mobile phones. As with most mobile apps, however, the majority of users abandon them quickly and after minimal use. One of the most critical factors for the success of a health app is how to support users’ commitment to their health. Despite increased interest from researchers in mobile health, few studies have examined the measurement of user engagement with health apps. Objective: User engagement is a multidimensional, complex phenomenon. The aim of this study was to understand the concept of user engagement and, in particular, to demonstrate the applicability of a user engagement scale (UES) to mobile health apps. Methods: To determine the measurability of user engagement in a mobile health context, a UES was employed, which is a psychometric tool to measure user engagement with a digital system. This was adapted to Ada, developed by Ada Health, an artificial intelligence–powered personalized health guide that helps people understand their health. A principal component analysis (PCA) with varimax rotation was conducted on 30 items. In addition, sum scores as means of each subscale were calculated. Results: Survey data from 73 Ada users were analyzed. PCA was determined to be suitable, as verified by the sampling adequacy of Kaiser-Meyer-Olkin=0.858, a significant Bartlett test of sphericity (χ2300=1127.1; P<.001), and communalities mostly within the 0.7 range. Although 5 items had to be removed because of low factor loadings, the results of the remaining 25 items revealed 4 attributes: perceived usability, aesthetic appeal, reward, and focused attention. Ada users showed the highest engagement level with perceived usability, with a value of 294, followed by aesthetic appeal, reward, and focused attention. Conclusions: Although the UES was deployed in German and adapted to another digital domain, PCA yielded consistent subscales and a 4-factor structure. This indicates that user engagement with health apps can be assessed with the German version of the UES. These results can benefit related mobile health app engagement research and may be of importance to marketers and app developers

Superconductivity in the two-dimensional Hubbard model?

A refined variational wave function for the two-dimensional repulsive Hubbard model is studied numerically, with the aim of approaching the difficult crossover regime of intermediate values of U. The issue of a superconducting ground state with d-wave symmetry is investigated for an average electron density n=0.8125 and for U=8t. Due to finite-size effects a clear-cut answer to this fundamental question has not yet been reached.Comment: 5 pages, 1 figure, Proc. 30th Int. Conf. of Theoretical Physics, Ustron, Poland, 2006, to be published in phys. stat. so

Labour Market Responses of survival pensioners: estimating a labour supply model and predicting the effect of the reform

In this paper we use a sample of administrative data coming from the `Dataware-house labour market and social protection' and the microsimulation model MIMOSIS to assess the labour supply effects of a reform of the rules for cumulating labour income with survival pension as proposed in the Generations Pact. In a first step we estimate a standard discrete choice labour supply model for several sub groups. Subsequently we model the proposed reform in the tax and benefit rules and we predict the change in desired labour supply of the targeted group. The reform has a significant positive effect on the labour supply of widows, but the effects are quite weak amongst the survivor pensioner with very low benefit, i.e. the group that was originally thought to benefit the most from the reform.Tax-benefit Systems { Microsimulation { Household Labour Supply