1,540 research outputs found
Interdependent Public Projects
In the interdependent values (IDV) model introduced by Milgrom and Weber
[1982], agents have private signals that capture their information about
different social alternatives, and the valuation of every agent is a function
of all agent signals. While interdependence has been mainly studied for
auctions, it is extremely relevant for a large variety of social choice
settings, including the canonical setting of public projects. The IDV model is
very challenging relative to standard independent private values, and welfare
guarantees have been achieved through two alternative conditions known as {\em
single-crossing} and {\em submodularity over signals (SOS)}. In either case,
the existing theory falls short of solving the public projects setting.
Our contribution is twofold: (i) We give a workable characterization of
truthfulness for IDV public projects for the largest class of valuations for
which such a characterization exists, and term this class \emph{decomposable
valuations}; (ii) We provide possibility and impossibility results for welfare
approximation in public projects with SOS valuations. Our main impossibility
result is that, in contrast to auctions, no universally truthful mechanism
performs better for public projects with SOS valuations than choosing a project
at random. Our main positive result applies to {\em excludable} public projects
with SOS, for which we establish a constant factor approximation similar to
auctions. Our results suggest that exclusion may be a key tool for achieving
welfare guarantees in the IDV model
A characterization of 2-player mechanisms for scheduling
We study the mechanism design problem of scheduling unrelated machines and we
completely characterize the decisive truthful mechanisms for two players when
the domain contains both positive and negative values. We show that the class
of truthful mechanisms is very limited: A decisive truthful mechanism
partitions the tasks into groups so that the tasks in each group are allocated
independently of the other groups. Tasks in a group of size at least two are
allocated by an affine minimizer and tasks in singleton groups by a
task-independent mechanism. This characterization is about all truthful
mechanisms, including those with unbounded approximation ratio.
A direct consequence of this approach is that the approximation ratio of
mechanisms for two players is 2, even for two tasks. In fact, it follows that
for two players, VCG is the unique algorithm with optimal approximation 2.
This characterization provides some support that any decisive truthful
mechanism (for 3 or more players) partitions the tasks into groups some of
which are allocated by affine minimizers, while the rest are allocated by a
threshold mechanism (in which a task is allocated to a player when it is below
a threshold value which depends only on the values of the other players). We
also show here that the class of threshold mechanisms is identical to the class
of additive mechanisms.Comment: 20 pages, 4 figures, ESA'0
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Approximate Strategyproofness
The standard approach of mechanism design theory insists on equilibrium behavior by participants. This assumption is captured by imposing incentive constraints on the design space. But in bridging from theory to practice, it often becomes necessary to relax incentive constraints in order to allow tradeoffs with other desirable properties. This article surveys a number of different options that can be adopted in relaxing incentive constraints, providing a current view of the state-of-the-art.Engineering and Applied Science
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