Fixed Price Approximability of the Optimal Gain From Trade

Bilateral trade is a fundamental economic scenario comprising a strategically acting buyer and seller, each holding valuations for the item, drawn from publicly known distributions. A mechanism is supposed to facilitate trade between these agents, if such trade is beneficial. It was recently shown that the only mechanisms that are simultaneously DSIC, SBB, and ex-post IR, are fixed price mechanisms, i.e., mechanisms that are parametrised by a price p, and trade occurs if and only if the valuation of the buyer is at least p and the valuation of the seller is at most p. The gain from trade is the increase in welfare that results from applying a mechanism; here we study the gain from trade achievable by fixed price mechanisms. We explore this question for both the bilateral trade setting, and a double auction setting where there are multiple buyers and sellers. We first identify a fixed price mechanism that achieves a gain from trade of at least 2/r times the optimum, where r is the probability that the seller's valuation does not exceed the buyer's valuation. This extends a previous result by McAfee. Subsequently, we improve this approximation factor in an asymptotic sense, by showing that a more sophisticated rule for setting the fixed price results in an expected gain from trade within a factor O(log(1/r)) of the optimal gain from trade. This is asymptotically the best approximation factor possible. Lastly, we extend our study of fixed price mechanisms to the double auction setting defined by a set of multiple i.i.d. unit demand buyers, and i.i.d. unit supply sellers. We present a fixed price mechanism that achieves a gain from trade that achieves for all epsilon > 0 a gain from trade of at least (1-epsilon) times the expected optimal gain from trade with probability 1 - 2/e^{#T epsilon^2 /2}, where #T is the expected number of trades resulting from the double auction

Efficiency Guarantees in Auctions with Budgets

In settings where players have a limited access to liquidity, represented in the form of budget constraints, efficiency maximization has proven to be a challenging goal. In particular, the social welfare cannot be approximated by a better factor then the number of players. Therefore, the literature has mainly resorted to Pareto-efficiency as a way to achieve efficiency in such settings. While successful in some important scenarios, in many settings it is known that either exactly one incentive-compatible auction that always outputs a Pareto-efficient solution, or that no truthful mechanism can always guarantee a Pareto-efficient outcome. Traditionally, impossibility results can be avoided by considering approximations. However, Pareto-efficiency is a binary property (is either satisfied or not), which does not allow for approximations. In this paper we propose a new notion of efficiency, called \emph{liquid welfare}. This is the maximum amount of revenue an omniscient seller would be able to extract from a certain instance. We explain the intuition behind this objective function and show that it can be 2-approximated by two different auctions. Moreover, we show that no truthful algorithm can guarantee an approximation factor better than 4/3 with respect to the liquid welfare, and provide a truthful auction that attains this bound in a special case. Importantly, the liquid welfare benchmark also overcomes impossibilities for some settings. While it is impossible to design Pareto-efficient auctions for multi-unit auctions where players have decreasing marginal values, we give a deterministic $O(\log n)$-approximation for the liquid welfare in this setting

Statistical Arbitrage Mining for Display Advertising

We study and formulate arbitrage in display advertising. Real-Time Bidding (RTB) mimics stock spot exchanges and utilises computers to algorithmically buy display ads per impression via a real-time auction. Despite the new automation, the ad markets are still informationally inefficient due to the heavily fragmented marketplaces. Two display impressions with similar or identical effectiveness (e.g., measured by conversion or click-through rates for a targeted audience) may sell for quite different prices at different market segments or pricing schemes. In this paper, we propose a novel data mining paradigm called Statistical Arbitrage Mining (SAM) focusing on mining and exploiting price discrepancies between two pricing schemes. In essence, our SAMer is a meta-bidder that hedges advertisers' risk between CPA (cost per action)-based campaigns and CPM (cost per mille impressions)-based ad inventories; it statistically assesses the potential profit and cost for an incoming CPM bid request against a portfolio of CPA campaigns based on the estimated conversion rate, bid landscape and other statistics learned from historical data. In SAM, (i) functional optimisation is utilised to seek for optimal bidding to maximise the expected arbitrage net profit, and (ii) a portfolio-based risk management solution is leveraged to reallocate bid volume and budget across the set of campaigns to make a risk and return trade-off. We propose to jointly optimise both components in an EM fashion with high efficiency to help the meta-bidder successfully catch the transient statistical arbitrage opportunities in RTB. Both the offline experiments on a real-world large-scale dataset and online A/B tests on a commercial platform demonstrate the effectiveness of our proposed solution in exploiting arbitrage in various model settings and market environments.Comment: In the proceedings of the 21st ACM SIGKDD international conference on Knowledge discovery and data mining (KDD 2015

Factors Affecting Quality of Life for Children with Asthma

BACKGROUND: In the U.S., asthma is the most common chronic illness in children under 18 years. An exploration of asthma admission rates in emergency departments indicated this was also the case for Southeast Georgia. Despite the availability of effective asthma treatments and interventions, asthma continues to severely impact children’s health-related QOL. PURPOSE: This exploratory study sought to assess quality of life (QOL) issues facing children with asthma and their caregivers. Specifically, this study aimed to 1) Determine the baseline QOL in children with asthma and their parents/caregivers, & 2) Determine what factors affect QOL for children with asthma and their caregivers. METHODS: This exploratory study employed a mixed-model design. Participants were recruited for a convenience sample from a large children’s hospital outpatient clinic in Southeast Georgia. Participants included children aged 7-17 with a diagnosis of asthma or reactive airway disease (N=104) and their parents/caregivers (N=104). Child participants completed the Paediatric Asthma Quality of Life Questionnaire (PAQLQ), a reliable and validated QOL questionnaire for childhood asthma focusing on the domains of activity limitations, emotional function, and an exploration of symptoms. Caregiver participants completed a demographics questionnaire and the Paediatric Asthma Caregiver’s Quality of Life Questionnaire (PACQLQ), a reliable and validated QOL questionnaire for caregivers of children with childhood asthma focusing on two domains, activity limitations and emotional function. Items in both the PAQLQ and PACQLQ questionnaires are rated on a 7-point scale, with higher scores indicating less impairment and lower scores indicating greater impairment to the domain under consideration. RESULTS & CLINICAL IMPLICATIONS: In addressing the first aim of this study, the results revealed that the baseline QOL for children with asthma and their caregivers was relatively high. In addressing the second aim of this study, the results of both the PAQLQ and the PACQLQ revealed that the most significant factor that affects the QOL of children with asthma is ED visits. The more ED visits reported, the greater the impairment to emotional function and physical activity. While the findings of this study demonstrate a positive baseline QOL, it is important to further investigate the specific impact of ED visits on QOL of children with asthma and their caregivers. An important clinical implication is that education on controlling asthma symptoms to prevent ED visits for both children and their caregivers may be of value to improve their QOL

Complete zygomatic arches in the Late Quaternary sloth Neocnus from La Altagracia province, Dominican Republic

Specimens of the extinct sloth genus Neocnus recovered from northwestern La Altagracia Province, Dominican Republic exhibit a unique zygomatic arch. The arch consists of the jugal anteriorly fused to the maxilla and the zygomatic arch ligament fully ossified between the jugal and the zygomatic process of the temporal bone. Evidence of the novel ossification is seen in adult and juvenile individuals. This occurrence is also unexpected as Neocnus individuals are 40 times smaller than the next sloth genus (e.g. Nothrotheriops) with a secondarily complete arch. No known species of Neocnus exhibits any of these jugal and zygomatic features and thus these specimens may represent a new species

A Model of Vertical Oligopolistic Competition

This paper develops a model of successive oligopolies with endogenous market entry, allowing for varying degrees of product differentiation and entry costs in both markets. Our analysis shows that the downstream conditions dominate the overall profitability of the two-tier structure while the upstream conditions mainly affect the distribution of profits. We compare the welfare effects of upstream versus downstream deregulation policies and show that the impact of deregulation may be overvalued when ignoring feedback effects from the other market. Furthermore, we analyze how different forms of vertical restraints influence the endogenous market structure and show when they are welfare enhancing

Pennsylvania Folklife Vol. 19, No. 2

• Powwowing in Berks County • Belsnickling in Paxtonville • The Folk Tradition of the Sweetheart Tree • Pigpens and Piglore in Rural Pennsylvania • Gravestones and Ostentation: A Study of Five Delaware County Cemeteries • Notes on Eighteenth-Century Emigration to the British Colonies • A Siegerland Emigrant List of 1738 • Local Place Names: Folk-Cultural Questionnaire No. 14https://digitalcommons.ursinus.edu/pafolklifemag/1038/thumbnail.jp