Price Dispersion in the Small and in the Large: Evidence from an Internet Price Comparison Site

This paper examines 4 million daily price observations for over 1000 consumer electronics products on the price comparison site Shopper.com. We find little support for the notion that prices on the Internet are converging to the “law of one price.” In addition, observed levels of price dispersion vary systematically with the number of firms listing prices. The difference between the two lowest prices (the “gap”) averages 22 percent when two firms list prices, and falls to 3.5 percent in markets where 17 firms list prices. These empirical results are an implication of a general “clearinghouse” model of equilibrium price dispersion.Bertrand Competition, Internet, Law of One Price, Price dispersion

Temporal Price Dispersion: Evidence from an Online Consumer Electronics Market

Economic theory indicates that E-retailers competing at price comparison sites, such as Shopper.com, must charge prices that cannot be systematically predicted by their rivals. Consistent with theory, we find significant variation in the identity of the lowprice firm as well as the level of the lowest price for 36 of the best-selling consumer electronics products sold at Shopper.com between November 1999 and May 2001. The observed pricing patterns can be explained by firms engaging in short-term price promotions in an attempt to avoid the deleterious outcome associated with price competition. Based on our arguments and the evidence presented, the managerial implications are clear: Strategic unpredictability in prices—through the use of hit and run sales—is a widely used and effective weapon for avoiding all-out price competition in online markets.Temporal price dispersion, price comparison sites, e-retail, sales promotion

Persistent Price Dispersion in Online Markets

Using data from one of the Internet’s leading price comparison sites for consumer electronics products, we present evidence for the persistence of price dispersion for 36 homogeneous products. The markets for these products are “thick” with an average of over 20 firms selling each product. We show that prices do not converge to the “law of one price” even after an 18 month period. This finding is robust to controls for differences in shipping charges and inventories. Further, we show that product life cycle effects lead to changes in the number of competing firms and the range of price dispersion consistent with the theoretical predictions of the Varian (1980) model. The average number of competing firms declines from about 28 to 10 during the final five months of our dataset. Over this same period, the average range in prices decreases from about 75 percent to 30 percent. After accounting for firm heterogeneities in costs, branding, reputation, trust, product availability and shipping costs, 28 percent of the variation in prices charged for homogeneous products remains unexplained. This is also consistent with the Varian model.Price dispersion, Internet, Law of One Price

Information, Search, and Price Dispersion

We provide a unified treatment of alternative models of information acquisition/transmission that have been advanced to rationalize price dispersion in online and offline markets for homogeneous products. These different frameworks -- which include sequential search, fixed sample search, and clearinghouse models -- reveal that reductions in (or the elimination of) consumer search costs need not reduce (or eliminate) price dispersion. Our treatment highlights a "duality" between search-theoretic and clearinghouse models of dispersion, and shows how auction-theoretic tools may be used to simplify (and even generalize) existing theoretical results. We conclude with an overview of the burgeoning empirical literature. The empirical evidence suggests that price dispersion in both online and offline markets is sizeable, pervasive, and persistent and does not purely stem from subtle differences in firms' products or services.

Diffraction-contrast imaging of cold atoms

We consider the inverse problem of in-line holography, applied to minimally-destructive imaging of cold atom clouds. Absorption imaging near-resonance provides a simple, but destructive measurement of atom column density. Imaging off resonance greatly reduces heating, and sequential images may be taken. Under the conditions required for off-resonant imaging, the generally-intractable inverse problem may be linearized. A minimally-destructive, quantitative and high-resolution image of the atom cloud column density is then retrieved from a single diffraction pattern.Comment: 4 pages, 3 figures v2: minor changes in response to referee reports, mostly additional experimental detail v3: revisions to figure 3: added trace and changed image. Minor text and referencing changes. Accepted by Phys Rev A (Rapid Commun

Heralded single photon sources: a route towards quantum communication technology and photon standards

Single photon counting, based on single photon sources and detectors, is a key ingredient for certain applications aiming at new quantum information technologies. Quantum cryptography, quantum radiometry, distributed quantum computing, as well as adjacent technologies such as biomedical and astronomical imaging, and low power classical communication also rely on single-photon technology. This paper reviews the present status of single photon sources and related counting measurement techniques, based on correlated (or heralded) photons in parametric down-conversion, and their possible impact on the above mentioned technologies, as well as an assessment for photon standards in the future

Framing the Immigration Policy Agenda: A Qualitative Comparative Analysis of Media Effects on Dutch Immigration Policies

This study applies a qualitative comparative analysis (QCA) design to examine how configurations of quantitative and qualitative aspects of media coverage associate with changes on the policy agenda. We analyze media coverage of sixteen focusing events related to Dutch immigration policies—an intractable policy controversy that is regularly under media scrutiny. In addition to the quantity of media attention, we take into account whether dominant framing in media coverage is contesting the current policy frame and whether the framing in the media is consonant. Our analysis indicates that frame contestation is a necessary condition for media effects. Quantity of media attention and frame consonance are relevant indicators of changes on the policy agenda only when the majority of media coverage is contesting the current policy frame. Furthermore, we found that in the case of intractable policy controversies, media f

Anharmonic Decay of Vibrational States in Amorphous Silicon

Anharmonic decay rates are calculated for a realistic atomic model of amorphous silicon. The results show that the vibrational states decay on picosecond timescales and follow the two-mode density of states, similar to crystalline silicon, but somewhat faster. Surprisingly little change occurs for localized states. These results disagree with a recent experiment.Comment: 10 pages, 4 Postscript figure