2,504 research outputs found
Spillovers in networks of user generated content : evidence from 23 natural experiments on Wikipedia
Endogeneity in network formation hinders the identification of the role that
social networks play in generating spillovers, peer effects and other externalities.
This paper tackles this problem and investigates how the link network between
articles on the German Wikipedia influences the attention and content generation
individual articles receive. Identification exploits local exogenous shocks on a small
number of nodes in the network. It can thus avoid the usually required, but strong,
assumptions of exogenous observed characteristics and link structure in networks.
Exogenous variation is generated by natural and technical disasters or by articles
being featured on the German Wikipediaâs start page. The effects on neighboring
pages are substantial; I observe an increase of almost 100 percent in terms of both
views and content generation. The aggregate effect over all neighbors is also large: I
find that a view on a treated article converts one for one into a view on a neighboring
article. However, the resulting content generation is small in absolute terms.
My approach also applies if, due to a lack of network data, identification through
partial overlaps in the network structure fails (e.g. in classrooms). It helps bridge
the gap between the experimental and social network literatures on peer effects
99 cent: Price points in e-commerce
Basu (2006) argues that the prevalence of 99 cent prices in shops can be explained with rational consumers who disregard the rightmost digits of the price. This bounded rational behaviour leads to a Bertrand equilibrium with positive markups. We use data from an Austrian price comparison site and find results highly compatible with Basu's theory. We can show that price points - in particular prices ending in 9 - are prevalent and have significant impact on consumer demand. Moreover, these price points are sticky; neither the price-setter itself wants to change them neither the rivals do underbid these prices, if they represent the cheapest price on the market. --Competitive Behaviour,Pricing Behaviour,E-Commerce,Pricing in the Nines,Focal Pricing
99 cent: Price Points in E-Commerce
Basu (2006) argues that the prevalence of 99 cent prices in shops can be explained with rational consumers who disregard the rightmost digits of the price. This bounded rational behaviour leads to a Bertrand equi- librium with positive markups. We use data from an Austrian price com- parison site and find results highly compatible with Basu's theory. We can show that price points - in particular prices ending in 9 - are preva- lent and have significant impact on consumer demand. Moreover, these price points are sticky; neither the price-setter itself wants to change them neither the rivals do underbid these prices, if they represent the cheapest price on the market.e-commerce, price comparison, price policy
Absolute conservation law for black holes
In all 2d theories of gravity a conservation law connects the (space-time
dependent) mass aspect function at all times and all radii with an integral of
the matter fields. It depends on an arbitrary constant which may be interpreted
as determining the initial value together with the initial values for the
matter field. We discuss this for spherically reduced Einstein-gravity in a
diagonal metric and in a Bondi-Sachs metric using the first order formulation
of spherically reduced gravity, which allows easy and direct fixations of any
type of gauge. The relation of our conserved quantity to the ADM and Bondi mass
is investigated. Further possible applications (ideal fluid, black holes in
higher dimensions or AdS spacetimes etc.) are straightforward generalizations.Comment: LaTex, 17 pages, final version, to appear in Phys. Rev.
When private information settles the bill : money and privacy in Google's market for smartphone applications
We shed light on a money-for-privacy trade-off in the market for smartphone applications (âappsâ). Developers offer their apps cheaper in return for greater access to personal information, and consumers choose between lower prices and more privacy. We provide evidence for this pattern using data on 300,000 mobile applications which were obtained from the Android Market in 2012 and 2014. We augmented these data with information from Alexa.com and Amazon Mechanical Turk. Our findings show that both the marketâs supply and the demand side consider an appâs ability to collect private information, measured by their use of privacy-sensitive permissions: (1) cheaper apps use more privacy-sensitive permissions; (2) installation numbers are lower for apps with sensitive permissions; (3) circumstantial factors,
such as the reputation of app developers, mitigate the strength of this relationship. Our results
emerge consistently across several robustness checks, including the use of panel data analysis, the use of selected matched âtwinâ-pairs of apps and the use of various alternative measures of privacy-sensitiveness
The Dimensional-Reduction Anomaly in Spherically Symmetric Spacetimes
In D-dimensional spacetimes which can be foliated by n-dimensional
homogeneous subspaces, a quantum field can be decomposed in terms of modes on
the subspaces, reducing the system to a collection of (D-n)-dimensional fields.
This allows one to write bare D-dimensional field quantities like the Green
function and the effective action as sums of their (D-n)-dimensional
counterparts in the dimensionally reduced theory. It has been shown, however,
that renormalization breaks this relationship between the original and
dimensionally reduced theories, an effect called the dimensional-reduction
anomaly. We examine the dimensional-reduction anomaly for the important case of
spherically symmetric spaces.Comment: LaTeX, 19 pages, 2 figures. v2: calculations simplified, references
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Money and privacy : Android market evidence
We study the role of privacy in the market for mobile applications. For such programs
used with smartphones and tablet PCs a very important market has emerged.
Yet, neither the role of privacy on that market is well understood, nor do we have
empirical evidence regarding its role therein. We exploit data on 300,000 mobile applications
and almost 600 âapplications-pairsâ to analyze both sides of this market:
First, we analyze the price that application suppliers charge for more privacy. Second,
we study how usersâ installations are related to the âpersonal data greedinessâ
of mobile applications.
We provide the first empirical evidence on the main assumptions of recent early
models on suppliersâ and consumersâ strategies in this market. Our results show
that (1) consumers take it into account when applications request rights to collect
private information and (2) suppliers ask for more rights if they offer an app for free
than if they offer it for a fee
Universal conservation law and modified Noether symmetry in 2d models of gravity with matter
It is well-known that all 2d models of gravity---including theories with
nonvanishing torsion and dilaton theories---can be solved exactly, if matter
interactions are absent. An absolutely (in space and time) conserved quantity
determines the global classification of all (classical) solutions. For the
special case of spherically reduced Einstein gravity it coincides with the mass
in the Schwarzschild solution. The corresponding Noether symmetry has been
derived previously by P. Widerin and one of the authors (W.K.) for a specific
2d model with nonvanishing torsion. In the present paper this is generalized to
all covariant 2d theories, including interactions with matter. The related
Noether-like symmetry differs from the usual one. The parameters for the
symmetry transformation of the geometric part and those of the matterfields are
distinct. The total conservation law (a zero-form current) results from a two
stage argument which also involves a consistency condition expressed by the
conservation of a one-form matter ``current''. The black hole is treated as a
special case.Comment: 3
Hawking Radiation for Non-minimally Coupled Matter from Generalized 2D Black Hole Models
It is well known that spherically symmetric reduction of General Relativity
(SSG) leads to non-minimally coupled scalar matter. We generalize (and correct)
recent results to Hawking radiation for a class of dilaton models which share
with the Schwarzschild black hole non-minimal coupling of scalar fields and the
basic global structure. An inherent ambiguity of such models (if they differ
from SSG) is discussed. However, for SSG we obtain the rather disquieting
result of a negative Hawking flux at infinity, if the usual recipe for such
calculations is applied.Comment: 8 page
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