Die Analyse von online vermitteltem Tausch, insbesondere derjenige bei Onlineauktionen, erfreut sich einiger Beliebtheit. Dafür gibt es neben der ökonomischen Bedeutung dieser Tauschform auch soziologische Gründe. Inzwischen zeigt eine beträchtliche Anzahl von Untersuchungen, dass online vermittelte Transaktionen durch ein Reputationssystem stabilisiert werden können. Dabei bewerten sich die beiden Transaktionspartner nach erfolgtem Tausch gegenseitig mittels eines von der Auktionsplattform bereitgestellten Bewertungssystems. Beide Tauschpartner haben die Möglichkeit, eine negative Bewertung mit einer ebensolchen zu vergelten, bzw. im Vorgriff darauf mit Vergeltung zu drohen, falls eine negative Bewertung erfolgen sollte. Es besteht hier also ein Kollektivgutproblem zweiter Ordnung, dessen Lösung Bedingung für eine stabile Gütertransaktion ist. In diesem Aufsatz wird analysiert, wie diese Stabilisierung theoretisch geschehen kann und welche empirischen Belege sich dafür anführen lassen. Dazu wird im nächsten Abschnitt vorerst der gesamte Tauschvorgang als ein zweifaches Vertrauensspiel modelliert und zwei einschlägige Lösungsansätze in Hypothesenform präsentiert. Dabei wird einmal von vollständig rationalen Akteuren und einmal von reziprok rationalen Akteuren ausgegangen. Die generierten Hypothesen werden anschließend anhand eines selbst erhobenen Datensatzes überprüft. Dieser enthält Angaben zu insgesamt 1800 Transaktionen und entsprechend 3600 potentiellen Bewertungen, die über eBay Deutschland getätigt wurden. Dabei wird neben der Analyse der Standardbewertungen insbesondere eine Analyse der dazugehörigen Freitextkommentare vorgenommen. Im vierten Abschnitt werden die Resultate theoretisch diskutiert und es wird auf der Basis der empirischen Ergebnisse zur Handlungsmotivation der Bewertenden ein Vorschlag gemacht, mit welchen institutionellen Maßnahmen der Bewertungsmechanismus verbessert werden könnte.

Os leilões na Internet têm ganhado muita popularidade, tornando-se uma das mais bem sucedidas formas de comércio eletrônico na atualidade. Apresento um modelo teórico para descrever um leilão ascendente, semelhante ao que ocorre na eBay, e verifico suas previsões comportamentais através de dois experimentos. Os resultados mostraram um distanciamento grande entre as previsões teóricas e o que foi observado na prática, no que se refere às estratégias utilizadas, mas acredito que isso se deva à falta de experiência dos participantes dos experimentos. Desenvolvo, então, programas que automatizam a coleta de dados de leilões de selos na eBay e analiso as variáveis que influenciam preços, número de compradores e lances iniciais (preços mínimos). Não houve surpresas em tal análise, no sentido de observar-se resultados contra-intuitivos, mas destaco a reputação dos vendedores como fator relevante para a determinação de preços finais e número de compradores participantes. Além disso, também destaco a ocorrência da submissão tardia de lances, fenômeno recorrente nos leilões na Internet. Proponho, por fim, um método simples que busca determinar o tipo de modelo de leilão, se de valor comum ou de valor privado, e aplico o método nos dados obtidos dos leilões de selos. O resultado foi o de que os leilões analisados estão enquadrados no modelo de valor comum. / Online auctions are one of the most popular and successful types of electronic commerce nowadays. I present a theoretical framework to address the kind of ascending auction implemented at eBay, and I check its predictions through two experiments. The results of the experiments did not confirm the theory, but I believe this is due to the bidders’ lack of previous experience. I also present an algorithm that automatically gathers data from auctions of stamps at eBay. These data is then used on an exploratory analysis that tries to shed some light on the determinants of final prices, minimum bids and the number of bidders. There were no surprises in this analysis, but I would highlight the measurable effect that seller’s reputation has on final prices and the number of bidders. Furthermore, it was possible to observe the occurrence of late bidding. At last, I propose a simple method that determines to which paradigm the on-line auction of stamps at eBay belongs: private value or common value. The result was that the auction of stamps at eBay belongs to the common value paradigm.

Thesis advisor: Hideo Konishi / Online auctions have many different formats. Each of these affect the ways in which users bid strategically. One example of this is the end-time format. Some sites, like eBay, use a hard close, under which there is a strict end-time and the highest bidder at that time wins. Others, like Amazon, have an extended end-time format. It has been shown that these differences do, in fact, appear to change how bidders behave. This paper uses data obtained from Yahoo! Auctions, where both formats are used, to examine the impact these differences have on the final price of an auction. / Thesis (BA) — Boston College, 2005. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Economics Honors Program.

This paper explores the determinants of the number of bidders and final price of 1900s oil paintings auctioned by resellers or dealers on eBay art auctions. We find that starting price has negative effect on bidder’s decision whether to enter the auctions or not while seller reputation variables such as seller´s feedback, being top rate seller has a positive effect. Furthermore, auction theory is introduced to study the bidder´s behavior through auction characteristics and final price. We find that, interestingly, the seller´s reputation variables have no significant effect to the final price and the number of bidders has positive effect toward final price of art work. This evidence means that art auctions on eBay has a private value auctions characteristic. However, some specific characteristics of online auctions, which are the last minute bidding and the presence of experienced bidders, significantly affect the final price. Being an experienced winner or using last minute bidding as a strategy substantially pay more than inexperienced winners or winners who do not use last minute bidding in auctioned painting. This could result from different preference of bidders toward auctioned painting or information on which each bidder is holding.

Thesis (M.S.)--Rochester Institute of Technology, 2008. / Typescript. Includes bibliographical references (leaves 22-25).

Os leilões na Internet têm ganhado muita popularidade, tornando-se uma das mais bem sucedidas formas de comércio eletrônico na atualidade. Apresento um modelo teórico para descrever um leilão ascendente, semelhante ao que ocorre na eBay, e verifico suas previsões comportamentais através de dois experimentos. Os resultados mostraram um distanciamento grande entre as previsões teóricas e o que foi observado na prática, no que se refere às estratégias utilizadas, mas acredito que isso se deva à falta de experiência dos participantes dos experimentos. Desenvolvo, então, programas que automatizam a coleta de dados de leilões de selos na eBay e analiso as variáveis que influenciam preços, número de compradores e lances iniciais (preços mínimos). Não houve surpresas em tal análise, no sentido de observar-se resultados contra-intuitivos, mas destaco a reputação dos vendedores como fator relevante para a determinação de preços finais e número de compradores participantes. Além disso, também destaco a ocorrência da submissão tardia de lances, fenômeno recorrente nos leilões na Internet. Proponho, por fim, um método simples que busca determinar o tipo de modelo de leilão, se de valor comum ou de valor privado, e aplico o método nos dados obtidos dos leilões de selos. O resultado foi o de que os leilões analisados estão enquadrados no modelo de valor comum. / Online auctions are one of the most popular and successful types of electronic commerce nowadays. I present a theoretical framework to address the kind of ascending auction implemented at eBay, and I check its predictions through two experiments. The results of the experiments did not confirm the theory, but I believe this is due to the bidders’ lack of previous experience. I also present an algorithm that automatically gathers data from auctions of stamps at eBay. These data is then used on an exploratory analysis that tries to shed some light on the determinants of final prices, minimum bids and the number of bidders. There were no surprises in this analysis, but I would highlight the measurable effect that seller’s reputation has on final prices and the number of bidders. Furthermore, it was possible to observe the occurrence of late bidding. At last, I propose a simple method that determines to which paradigm the on-line auction of stamps at eBay belongs: private value or common value. The result was that the auction of stamps at eBay belongs to the common value paradigm.

Die Analyse von online vermitteltem Tausch, insbesondere derjenige bei Onlineauktionen, erfreut sich einiger Beliebtheit. Dafür gibt es neben der ökonomischen Bedeutung dieser Tauschform auch soziologische Gründe. Inzwischen zeigt eine beträchtliche Anzahl von Untersuchungen, dass online vermittelte Transaktionen durch ein Reputationssystem stabilisiert werden können. Dabei bewerten sich die beiden Transaktionspartner nach erfolgtem Tausch gegenseitig mittels eines von der Auktionsplattform bereitgestellten Bewertungssystems. Beide Tauschpartner haben die Möglichkeit, eine negative Bewertung mit einer ebensolchen zu vergelten, bzw. im Vorgriff darauf mit Vergeltung zu drohen, falls eine negative Bewertung erfolgen sollte. Es besteht hier also ein Kollektivgutproblem zweiter Ordnung, dessen Lösung Bedingung für eine stabile Gütertransaktion ist. In diesem Aufsatz wird analysiert, wie diese Stabilisierung theoretisch geschehen kann und welche empirischen Belege sich dafür anführen lassen. Dazu wird im nächsten Abschnitt vorerst der gesamte Tauschvorgang als ein zweifaches Vertrauensspiel modelliert und zwei einschlägige Lösungsansätze in Hypothesenform präsentiert. Dabei wird einmal von vollständig rationalen Akteuren und einmal von reziprok rationalen Akteuren ausgegangen. Die generierten Hypothesen werden anschließend anhand eines selbst erhobenen Datensatzes überprüft. Dieser enthält Angaben zu insgesamt 1800 Transaktionen und entsprechend 3600 potentiellen Bewertungen, die über eBay Deutschland getätigt wurden. Dabei wird neben der Analyse der Standardbewertungen insbesondere eine Analyse der dazugehörigen Freitextkommentare vorgenommen. Im vierten Abschnitt werden die Resultate theoretisch diskutiert und es wird auf der Basis der empirischen Ergebnisse zur Handlungsmotivation der Bewertenden ein Vorschlag gemacht, mit welchen institutionellen Maßnahmen der Bewertungsmechanismus verbessert werden könnte.

Lucking-Reiley (2000) 提到eBay 是全世界最大消費者導向拍賣之 一。Bajari and Hortacsu (2004) 指出線上拍賣存在資訊不對稱， 本研究觀察eBay 拍賣網站潛在競標者對DVD 標的的出價行為，亦即，觀察 得標價如何被決定及競標者的出價策略為何。 本研究結論如下：起標價格、賣方聲望回饋、出價次數對得標價 為正向影響且顯著，拍賣天數對得標價為正向效果但不顯著。賣方聲 望回饋愈高，愈有經驗競標者的出價策略是愈晚出價。競標者出價策 略為晚出價， 採取自動出價並出價一次。

Online auctions are arguably one of the most important and distinctly new applications of the internet. The predominant player in online auctions, eBay, has over 18.9 milllion users, and it was the host of over $5 billion worth of goods sold in the year 2000. Using methods from approximate dynamic programming and integer programming, we design algorithms for optimally bidding for a single item online auction, and simultaneous or overlapping multiple online auctions. We report computational evidence using data from eBay's web site from 1772 completed auctions for personal digital assistants and from 4208 completed auctions for stamp collections that show that (a) the optimal dynamic strategy outperforms simple but widely used static heuristic rules for a single auction, and (b) a new approach combining the value functions of single auctions found by dynamic programming using an integer programming framework produces high quality solutions fast and reliably. / Singapore-MIT Alliance (SMA)

The major internet auction sites eBay and Yahoo have developed innovative hybrid auction designs that incorporate buy prices. My dissertation focuses on the Buy It Now (BIN, hereafter) version of the auctions on eBay, the largest online auction site. The BIN hybrid auction combines a standard ascending bid auction with a posted-price offer. A seller in a BIN auction lists his auction with a "buy price". A bidder may purchase the item immediately at the buy price and end the auction. If he places a bid instead, the option to purchase the item at the buy price disappears and the subsequent bidders participate in the standard eBay auction. This auction format has been very popular with both buyers and sellers. In 2005 eBay's sales in fixed price platform (BIN and Half.com) totaled $13.8 billion, which was 33.1% of eBay's total sales.The dissertation explores the BIN auctions using theory, experiments and field data. Chapter 1 theoretically analyzes BIN auctions within the common values framework. An equilibrium is characterized, shown to exist, and the revenues generated by BIN and standard eBay auctions are compared. Chapter 2 compares the bidding behavior and the revenue implications of BIN auctions in lab experiments under common and private value assumptions. The third develops an "incomplete" theoretical model of BIN auctions within the private values framework. An "incomplete" empirical specification is derived and then field data collected from eBay's BIN auctions are used to estimate the primitives of the model, including the bidders' risk aversion and time preference. I then explore how heterogeneity of sellers and items influence these primitives. Chapter 1 (Common Values Auctions with a Buy Price: the case of eBay): Several explanations for the popularity of buy price have been provided for independent private value auctions. Risk aversion and impatience of either the bidders or the seller have mainly been used to explain the popularity of buy prices in IPV models. This paper, using a pure common value framework, models auctions with eBay-style "temporary" buy prices, when the bidders and the seller are either risk neutral or risk averse. It characterizes equilibrium bidding strategies in a general setup and then analyzes a seller's incentive to post a buy price when there are two bidders. When bidders are either risk neutral or risk averse there is no incentive to post a buy price for a risk neutral seller. But when the seller is risk averse, a suitably chosen buy price can raise the seller's expected utility when the bidders are either risk neutral or risk averse. Chapter 2 (An Experimental Study of Auctions with a Buy Price Under Private and Common Values): We use experiments to examine several predictions from the theoretical studies of buy prices. The theoretical predictions from Wooders and Reynolds (2003) and Chapter 1 show that the introduction of a buy price causes the seller's revenue to move in opposite directions in private value and common value settings. Meanwhile, Mathews and Katzman (2006) find that risk averse sellers might find buy prices advantageous because they reduce the variance in seller revenue in eBay auctions with risk-neutral bidders. The lab experiments are used to answer three key questions. (a) Can a buy price raise seller revenue and lower the variance of seller revenue in an independent private value auction? (b) Does a buy price lower seller revenue in common value auctions? (c) If the theoretical predictions do not hold, can a behavioral model explain the patterns observed in the data? Using a between-subjects design the results show that the use of a buy price has a positive and statistically significant effect on seller revenue in private value auctions. The buyers are risk averse. The estimate of the Constant Absolute Risk Aversion (CARA) index of 1.11 for the bidders is equivalent to a Constant Relative Risk Aversion (CRRA) index of 0.62 which is centered within the range of other estimates of relative risk aversion. As predicted by the theory when buyers are risk averse, the use of a buy price yields a statistically significant reduction in the variance of seller revenue. Hence, as predicted, the use of a buy price is advantageous to the seller when either the bidders or the seller are risk averse. The results for common value auctions are inconsistent with the theoretical predictions. Use of a buy price did not lower seller revenue, and the bidders' behavior departed from theoretical predictions in several respects. As a result, we develop and estimate a behavioral model of common value BIN auctions based on the winner's curse and overweighting of a bidder's private information. We find statistically significant evidence of overweighting of the bidder's own signal and estimated a CARA index of 0.001. This behavioral model explains all the departures from the rational model we found in the common values experiments. Chapter 3 (The Buy-it-now Option, Risk Aversion, and Impatience in an Empirical Model of eBay Bidding): Haile and Tamer (2003) first used an incomplete econometric model in an auction context, assuming that bidders bid up to their values and do not allow an opponent to win at a price they are willing to beat. Canals-Cerda and Pearcy (2004) used a similar incomplete econometric model to study eBay auctions while adding the assumption that the maximum of all the bids placed by the bidder with the second highest value is exactly equal to his value. Chapter 3 extends these incomplete models to eBay's BIN auctions. We develop and estimate an equilibrium model for BIN independent private value auctions with a stochastic and unknown number of potential bidders who enter the auction sequentially. In the model risk averse and time impatient bidders buy at the BIN price because it allows them to avoid the uncertainties and delay of the ascending bid auction that takes place if no one chooses the BIN option. As a result, the bidders' decisions to choose the BIN option in BIN auctions of different lengths can be used to identify the bidders' risk aversion and time preference parameters. Our model is "incomplete" in the sense that we do not impose any stylized structure on bidding in the ascending bid auction and, although bid revision is allowed, the process is not explicitly described. Our "incomplete" econometric model uses a partial likelihood approach proposed by Cox (1975) that allows the analysis to bypass modeling bidding and the bid revision process. The model is estimated using a new data set of 3245 eBay auctions of Pentium-3 laptops that ran between 22 July to 10 August 2005.