Mechanism design, sometimes called implementation theory or institutiondesign,[1] is a branch of economics, social choice, and game theory that deals with designing game forms (or mechanisms) to implement a given social choice function. Because it starts with the end of the game (an optimal result) and then works backwards to find a game that implements it, it is sometimes described as reverse game theory.[2]
Mechanism design studies solution concepts for a class of private-information games. Leonid Hurwicz explains that "in a design problem, the goal function is the main given, while the mechanism is the unknown. Therefore, the design problem is the inverse of traditional economic theory, which is typically devoted to the analysis of the performance of a given mechanism."[3]
One person, called the "principal", would like to condition his behavior on information privately known to the players of a game. For example, the principal would like to know the true quality of a used car a salesman is pitching. He cannot learn anything simply by asking the salesman, because it is in the salesman's interest to distort the truth. However, in mechanism design, the principal does have one advantage: He may design a game whose rules influence others to act the way he would like.
Without mechanism design theory, the principal's problem would be difficult to solve. He would have to consider all the possible games and choose the one that best influences other players' tactics. In addition, the principal would have to draw conclusions from agents who may lie to him. Thanks to the revelation principle, the principal only needs to consider games in which agents truthfully report their private information.
Foundations
Mechanism
A game of mechanism design is a game of private information in which one of the agents, called the principal, chooses the payoff structure. Following Harsanyi (1967), the agents receive secret "messages" from nature containing information relevant to payoffs. For example, a message may contain information about their preferences or the quality of a good for sale. We call this information the agent's "type" (usually noted and accordingly the space of types ). Agents then report a type to the principal (usually noted with a hat ) that can be a strategic lie. After the report, the principal and the agents are paid according to the payoff structure the principal chose.
The timing of the game is:
The principal commits to a mechanism that grants an outcome as a function of reported type
The agents report, possibly dishonestly, a type profile
The mechanism is executed (agents receive outcome )
In order to understand who gets what, it is common to divide the outcome into a goods allocation and a money transfer, where stands for an allocation of goods rendered or received as a function of type, and stands for a monetary transfer as a function of type.
As a benchmark the designer often defines what should happen under full information. Define a social choice function mapping the (true) type profile directly to the allocation of goods received or rendered,
In contrast a mechanism maps the reported type profile to an outcome (again, both a goods allocation and a money transfer )
A proposed mechanism constitutes a Bayesian game (a game of private information), and if it is well-behaved the game has a Bayesian Nash equilibrium. At equilibrium agents choose their reports strategically as a function of type
It is difficult to solve for Bayesian equilibria in such a setting because it involves solving for agents' best-response strategies and for the best inference from a possible strategic lie. Thanks to a sweeping result called the revelation principle, no matter the mechanism a designer can[5] confine attention to equilibria in which agents truthfully report type. The revelation principle states: "To every Bayesian Nash equilibrium there corresponds a Bayesian game with the same equilibrium outcome but in which players truthfully report type."
This is extremely useful. The principle allows one to solve for a Bayesian equilibrium by assuming all players truthfully report type (subject to an incentive compatibility constraint). In one blow it eliminates the need to consider either strategic behavior or lying.
Its proof is quite direct. Assume a Bayesian game in which the agent's strategy and payoff are functions of its type and what others do, . By definition agent i's equilibrium strategy is Nash in expected utility:
Simply define a mechanism that would induce agents to choose the same equilibrium. The easiest one to define is for the mechanism to commit to playing the agents' equilibrium strategies for them.
Under such a mechanism the agents of course find it optimal to reveal type since the mechanism plays the strategies they found optimal anyway. Formally, choose such that
The designer of a mechanism generally hopes either
to design a mechanism that "implements" a social choice function
to find the mechanism that maximizes some value criterion (e.g. profit)
To implement a social choice function is to find some transfer function that motivates agents to pick . Formally, if the equilibrium strategy profile under the mechanism maps to the same goods allocation as a social choice function,
we say the mechanism implements the social choice function.
Thanks to the revelation principle, the designer can usually find a transfer function to implement a social choice by solving an associated truthtelling game. If agents find it optimal to truthfully report type,
we say such a mechanism is truthfully implementable. The task is then to solve for a truthfully implementable and impute this transfer function to the original game. An allocation is truthfully implementable if there exists a transfer function such that
which is also called the incentive compatibility (IC) constraint.
In applications, the IC condition is the key to describing the shape of in any useful way. Under certain conditions it can even isolate the transfer function analytically. Additionally, a participation (individual rationality) constraint is sometimes added if agents have the option of not playing.
Necessity
Consider a setting in which all agents have a type-contingent utility function . Consider also a goods allocation that is vector-valued and size (which permits number of goods) and assume it is piecewise continuous with respect to its arguments.
The function is implementable only if
whenever and and x is continuous at . This is a necessary condition and is derived from the first- and second-order conditions of the agent's optimization problem assuming truth-telling.
Its meaning can be understood in two pieces. The first piece says the agent's marginal rate of substitution (MRS) increases as a function of the type,
In short, agents will not tell the truth if the mechanism does not offer higher agent types a better deal. Otherwise, higher types facing any mechanism that punishes high types for reporting will lie and declare they are lower types, violating the truthtelling incentive-compatibility constraint. The second piece is a monotonicity condition waiting to happen,[clarification needed]
which, to be positive, means higher types must be given more of the good.
There is potential for the two pieces to interact. If for some type range the contract offered less quantity to higher types , it is possible the mechanism could compensate by giving higher types a discount. But such a contract already exists for low-type agents, so this solution is pathological. Such a solution sometimes occurs in the process of solving for a mechanism. In these cases it must be "ironed". In a multiple-good environment it is also possible for the designer to reward the agent with more of one good to substitute for less of another (e.g. butter for margarine). Multiple-good mechanisms are an area of continuing research in mechanism design.
Sufficiency
Mechanism design papers usually make two assumptions to ensure implementability:
This is known by several names: the single-crossing condition, the sorting condition and the Spence–Mirrlees condition. It means the utility function is of such a shape that the agent's MRS is increasing in type.[clarification needed]
This is a technical condition bounding the rate of growth of the MRS.
These assumptions are sufficient to provide that any monotonic is implementable (a exists that can implement it). In addition, in the single-good setting the single-crossing condition is sufficient to provide that only a monotonic is implementable, so the designer can confine his search to a monotonic .
Vickrey (1961) gives a celebrated result that any member of a large class of auctions assures the seller of the same expected revenue and that the expected revenue is the best the seller can do. This is the case if
The buyers have identical valuation functions (which may be a function of type)
The type distribution bears the monotone hazard rate property
The mechanism sells the good to the buyer with the highest valuation
The last condition is crucial to the theorem. An implication is that for the seller to achieve higher revenue he must take a chance on giving the item to an agent with a lower valuation. Usually this means he must risk not selling the item at all.
The Vickrey (1961) auction model was later expanded by Clarke (1971) and Groves to treat a public choice problem in which a public project's cost is borne by all agents, e.g. whether to build a municipal bridge. The resulting "Vickrey–Clarke–Groves" mechanism can motivate agents to choose the socially efficient allocation of the public good even if agents have privately known valuations. In other words, it can solve the "tragedy of the commons"—under certain conditions, in particular quasilinear utility or if budget balance is not required.
Consider a setting in which number of agents have quasilinear utility with private valuations where the currency is valued linearly. The VCG designer designs an incentive compatible (hence truthfully implementable) mechanism to obtain the true type profile, from which the designer implements the socially optimal allocation
The cleverness of the VCG mechanism is the way it motivates truthful revelation. It eliminates incentives to misreport by penalizing any agent by the cost of the distortion he causes. Among the reports the agent may make, the VCG mechanism permits a "null" report saying he is indifferent to the public good and cares only about the money transfer. This effectively removes the agent from the game. If an agent does choose to report a type, the VCG mechanism charges the agent a fee if his report is pivotal, that is if his report changes the optimal allocation x so as to harm other agents. The payment is calculated
which sums the distortion in the utilities of the other agents (and not his own) caused by one agent reporting.
Myerson and Satterthwaite (1983) show there is no efficient way for two parties to trade a good when they each have secret and probabilistically varying valuations for it, without the risk of forcing one party to trade at a loss. It is among the most remarkable negative results in economics—a kind of negative mirror to the fundamental theorems of welfare economics.
Phillips and Marden (2018) proved that for cost-sharing games with concave cost functions, the optimal cost-sharing rule that firstly optimizes the worst-case inefficiencies in a game (the price of anarchy), and then secondly optimizes the best-case outcomes (the price of stability), is precisely the Shapley value cost-sharing rule.[6] A symmetrical statement is similarly valid for utility-sharing games with convex utility functions.
Price discrimination
Mirrlees (1971) introduces a setting in which the transfer function t() is easy to solve for. Due to its relevance and tractability it is a common setting in the literature. Consider a single-good, single-agent setting in which the agent has quasilinear utility with an unknown type parameter
and in which the principal has a prior CDF over the agent's type . The principal can produce goods at a convex marginal cost c(x) and wants to maximize the expected profit from the transaction
subject to IC and IR conditions
The principal here is a monopolist trying to set a profit-maximizing price scheme in which it cannot identify the type of the customer. A common example is an airline setting fares for business, leisure and student travelers. Due to the IR condition it has to give every type a good enough deal to induce participation. Due to the IC condition it has to give every type a good enough deal that the type prefers its deal to that of any other.
A trick given by Mirrlees (1971) is to use the envelope theorem to eliminate the transfer function from the expectation to be maximized,
Integrating,
where is some index type. Replacing the incentive-compatible in the maximand,
after an integration by parts. This function can be maximized pointwise.
Because is incentive-compatible already the designer can drop the IC constraint. If the utility function satisfies the Spence–Mirrlees condition then a monotonic function exists. The IR constraint can be checked at equilibrium and the fee schedule raised or lowered accordingly. Additionally, note the presence of a hazard rate in the expression. If the type distribution bears the monotone hazard ratio property, the FOC is sufficient to solve for t(). If not, then it is necessary to check whether the monotonicity constraint (see sufficiency, above) is satisfied everywhere along the allocation and fee schedules. If not, then the designer must use Myerson ironing.
Myerson ironing
In some applications the designer may solve the first-order conditions for the price and allocation schedules yet find they are not monotonic. For example, in the quasilinear setting this often happens when the hazard ratio is itself not monotone. By the Spence–Mirrlees condition the optimal price and allocation schedules must be monotonic, so the designer must eliminate any interval over which the schedule changes direction by flattening it.
Intuitively, what is going on is the designer finds it optimal to bunch certain types together and give them the same contract. Normally the designer motivates higher types to distinguish themselves by giving them a better deal. If there are insufficiently few higher types on the margin the designer does not find it worthwhile to grant lower types a concession (called their information rent) in order to charge higher types a type-specific contract.
Consider a monopolist principal selling to agents with quasilinear utility, the example above. Suppose the allocation schedule satisfying the first-order conditions has a single interior peak at and a single interior trough at , illustrated at right.
Following Myerson (1981) flatten it by choosing satisfying where is the inverse function of x mapping to and is the inverse function of x mapping to . That is, returns a before the interior peak and returns a after the interior trough.
If the nonmonotonic region of borders the edge of the type space, simply set the appropriate function (or both) to the boundary type. If there are multiple regions, see a textbook for an iterative procedure; it may be that more than one troughs should be ironed together.
Proof
The proof uses the theory of optimal control. It considers the set of intervals in the nonmonotonic region of over which it might flatten the schedule. It then writes a Hamiltonian to obtain necessary conditions for a within the intervals
that does satisfy monotonicity
for which the monotonicity constraint is not binding on the boundaries of the interval
Condition two ensures that the satisfying the optimal control problem reconnects to the schedule in the original problem at the interval boundaries (no jumps). Any satisfying the necessary conditions must be flat because it must be monotonic and yet reconnect at the boundaries.
As before maximize the principal's expected payoff, but this time subject to the monotonicity constraint
and use a Hamiltonian to do it, with shadow price
where is a state variable and the control. As usual in optimal control the costate evolution equation must satisfy
Taking advantage of condition 2, note the monotonicity constraint is not binding at the boundaries of the interval,
meaning the costate variable condition can be integrated and also equals 0
The average distortion of the principal's surplus must be 0. To flatten the schedule, find an such that its inverse image maps to a interval satisfying the condition above.
^In unusual circumstances some truth-telling games have more equilibria than the Bayesian game they mapped from. See Fudenburg-Tirole Ch. 7.2 for some references.
^Phillips, Matthew; Marden, Jason R. (July 2018). "Design Tradeoffs in Concave Cost-Sharing Games". IEEE Transactions on Automatic Control. 63 (7): 2242–2247. doi:10.1109/tac.2017.2765299. ISSN0018-9286. S2CID45923961.
Harsanyi, John C. (1967). "Games with incomplete information played by "Bayesian" players, I-III. part I. The Basic Model". Management Science. 14 (3): 159–182. doi:10.1287/mnsc.14.3.159. JSTOR2628393.
Satterthwaite, Mark Allen (1975). "Strategy-proofness and Arrow's conditions: Existence and correspondence theorems for voting procedures and social welfare functions". Journal of Economic Theory. 10 (2): 187–217. CiteSeerX10.1.1.471.9842. doi:10.1016/0022-0531(75)90050-2.
Roger B. Myerson (2008), "Mechanism Design", The New Palgrave Dictionary of Economics Online, Abstract.
Diamantaras, Dimitrios (2009), A Toolbox for Economic Design, New York: Palgrave Macmillan, ISBN978-0-230-61060-6. A graduate text specifically focused on mechanism design.
Kancah[1] atau kawah[2] (bahasa Inggris: cauldron)[3] adalah kuali besar yang digunakan untuk memasak makanan atau minuman pada Zaman Tembaga dan Zaman Besi.[4] Kaldron yang pernah ditemukan di Inggris dan Irlandia terbuat dari tembaga, besi, atau campuran keduanya.[4] Di era modern, kaldron digunakan di dalam upacara olimpiade olahraga sebagai tempat api olimpiade dinyalakan untuk simbol pembukaan acara.[5] Etimologi Kata cauldron pertama k...
Dieser Artikel behandelt den Fluss. Zum gleichnamigen sudanesischen Staat siehe an-Nil al-azraq. Blauer Nil Abbai Blauer Nil unterhalb Bahar Dar Blauer Nil unterhalb Bahar Dar Daten Lage im Hochland vonAthiopien Äthiopienund im Osten desSudan Sudan Flusssystem Nil Abfluss über Nil → Mittelmeer Quelle Bei Gish Abay als Gilgel Abay (Kleiner Abbai)[1][2]10° 58′ 12″ N, 37° 11′ 54″ O10.9699353...
AdradasNegara SpanyolKomunitas otonomiCastile dan LeonProvinsiSoriaMunisipalitasAdradasLuas • Total67 km2 (26 sq mi)Populasi (2004) • Total86 • Kepadatan1,3/km2 (30/sq mi)Zona waktuUTC+1 (CET) • Musim panas (DST)UTC+2 (CEST) Adradas adalah kotamadya yang terletak di departemen provinsi Soria, Castile dan Leon, Spanyol. Kotamadya Adradas memiliki luas sebesar 67,47 km². Kotamadya Adradas memiliki penduduk seban...
Запрос «Пятый канал» перенаправляется сюда; см. также другие значения. Запрос «Ленинградское телевидение» перенаправляется сюда; о телевещании в Ленинграде и Санкт-Петербурге см. Телевидение в Санкт-Петербурге. Пятый каналАО «Телерадиокомпания „Петербург“» Стра�...
For the Cossack peoples of Eastern Europe, see Cossacks. 1863 novel by Leo Tolstoy The Cossacks Portrait of a Cossack by Alexander LitovchenkoAuthorLeo TolstoyOriginal titleКазаки (Kozaky)TranslatorEugene Schuyler (1878), Peter Constantine (2004)CountryRussiaLanguageRussianGenreFictionPublisherThe Russian MessengerPublication date1863Published in English1878 (Scribner's)Pages161 p. (Paperback)ISBN0-679-64291-9 Wikisource has original text related to this article: The Cossacks ...
Australian art critic, art historian and artist (1907–1992) Alan McLeod McCullochAOAlan McCulloch c.1934Born(1907-08-05)August 5, 1907St Kilda, VictoriaDiedDecember 21, 1992(1992-12-21) (aged 85)Kew, VictoriaEducationScotch College; Working Men's College, Melbourne; National Gallery of Victoria Art SchoolGenreencyclopaedist, journalist, cartoonist, visual artistSubjectart criticism, Australian art history, humourYears active1935–1991Notable worksThe Encyclopedia of Australian Ar...
Bupati Humbang HasundutanBadge Bupati Humbang HasundutanPetahanaDosmar Banjarnahorsejak 26 Februari 2021Dibentuk28 Juli 2003; 20 tahun lalu (2003-07-28)Pejabat pertamaManatap SimanungkalitSitus webhumbanghasundutankab.go.id Daftar Bupati Kabupaten Humbang Hasundutan di bawah ini adalah para pejabat Kepala Daerah Kabupaten Humbang Hasundutan sejak dibentuk pada tanggal 28 Juli 2003 berdasarkan UU No. 9 Tahun 2003. No Bupati Mulai menjabat Akhir menjabat Prd. Ket. Wakil Bupati — Man...
Railway station in Turpan, China Turpan North吐鲁番北General informationLocationGaochang District, Turpan, XinjiangChinaOperated byChina RailwayLine(s) Lanzhou–Xinjiang high-speed railway ConnectionsTurpan Jiaohe AirportHistoryOpened2014 (2014) Turpan North railway station (Chinese: 吐鲁番北站) is a railway station on the Lanzhou–Xinjiang high-speed railway, serving the city of Turpan in Xinjiang, China. The station is located about 10 km northwest from the city center, ...
Cumulus castellanusCumulus castellanus low on the horizonAppearanceFlat on the bottom, though has multiple towers on topPrecipitationUsually, but not always Cumulus castellanus (from Latin castellanus, castle) is an unofficial name of a species of cumulus cloud that is distinctive because it displays multiple towers arising from its top, indicating significant vertical air movement. It is a misnomer for cumulus congestus and correspondingly can be an indicator of forthcoming showers and thund...
Women's national football team representing England Lionesses redirects here. For other uses, see Lioness (disambiguation). EnglandNickname(s)The Lionesses[1]AssociationThe Football Association (The FA)ConfederationUEFA (Europe)Head coachSarina WiegmanCaptainLeah WilliamsonMost capsFara Williams (172)Top scorerEllen White (58)FIFA codeENG First colours Second colours FIFA rankingCurrent 2 2 (15 March 2024)[2]Highest2 (March 2018; March 2024)Lowest14 (June 2004 – September 20...
Untuk kegunaan lain, lihat Mars (disambiguasi). Penyuntingan Artikel oleh pengguna baru atau anonim untuk saat ini tidak diizinkan.Lihat kebijakan pelindungan dan log pelindungan untuk informasi selengkapnya. Jika Anda tidak dapat menyunting Artikel ini dan Anda ingin melakukannya, Anda dapat memohon permintaan penyuntingan, diskusikan perubahan yang ingin dilakukan di halaman pembicaraan, memohon untuk melepaskan pelindungan, masuk, atau buatlah sebuah akun. Mars Citra Mars yang diabadikan o...
Oak ParkStasiun komuter PTVLokasiWaterloo Road, Oak ParkMelbourne, VictoriaAustraliaPemilikVicTrackOperatorMetro TrainsJalur CraigieburnJumlah peron2 sisiJumlah jalur2KonstruksiJenis strukturTanahParkir37Informasi lainZona tarifMyki Zona 1/2Situs webPublic Transport VictoriaSejarahDibuka13 Agustus 1956Operasi layanan Stasiun sebelumnya Metro Trains Stasiun berikutnya Pascoe Valemenuju Flinders Street Jalur CraigieburnGlenroymenuju Craigieburn Sunting kotak info �...
Lowest energy level of a quantum system Energy levels for an electron in an atom: ground state and excited states. After absorbing energy, an electron may jump from the ground state to a higher-energy excited state. The ground state of a quantum-mechanical system is its stationary state of lowest energy; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater than the ground state. In quantum field theory, the ground st...
Chinese jelly made of mung bean starch For the southern Chinese dessert, see grass jelly. LiangfenSichuan-style liangfenTraditional Chinese涼粉Simplified Chinese凉粉Hanyu Pinyinliángfěn Literal meaningcool powderTranscriptionsStandard MandarinHanyu PinyinliángfěnYue: CantoneseJyutpingloeng4 fen2 Liangfen (simplified Chinese: 凉粉; traditional Chinese: 涼粉; pinyin: liángfěn; lit. 'cool powder'), also spelled liang fen, is a Chinese legume dish consisting...
Македонська заявка на вступ до ЄС Статус КандидатЗаявку подано 24 березня 2004Заявку схвалено 17 грудня 2005Початок перемовин 19 липня 2022Прогрес ПеремовиниХід скринінгу 0% виконано Закриті розділи Поки що не виконаноХід ратифікації Поки що не виконано Статистичне порівняння ...
Mappa delle prefetture e delle regioni del Giappone. Le prefetture del Giappone sono le 47 divisioni territoriali di primo livello in cui è suddiviso il paese. Viene compresa in tale computo anche la metropoli (都?, To) di Tokyo, le cui funzioni sono equiparabili a quelle delle prefetture. Le altre 46 comprendono il circuito (道?, Dō) di Hokkaidō, le due prefetture urbane (府?, Fu) di Osaka e Kyoto, e 43 altre prefetture (県?, Ken). In giapponese, l'insieme delle 4 suddivisioni di live...
American businessman (1924–2023) Charles Munger redirects here. For the politician, see Charles Henry Munger. Charlie MungerMunger in 2010BornCharles Thomas Munger(1924-01-01)January 1, 1924Omaha, Nebraska, U.S.DiedNovember 28, 2023(2023-11-28) (aged 99)Santa Barbara, California, U.S.EducationUniversity of MichiganCalifornia Institute of TechnologyHarvard University (JD)OccupationsBusinessmanfinancial analystinvestorphilanthropistlawyerKnown forVice Chairman, Berkshire Hathaw...
Pour les articles homonymes, voir Liévin (homonymie). Liévin de GandLe Martyre de Saint Liévin, Rubens (1633), musées royaux des Beaux-Arts de Belgique.FonctionÉvêqueBiographieNaissance Vers 580IrlandeDécès 12 novembre 657Essche-Saint-LiévinActivité MissionnairePériode d'activité VIIe siècleAutres informationsÉtape de canonisation SaintFête 12 novembremodifier - modifier le code - modifier Wikidata Saint Liévin, œuvre de Laurent Delvaux, musée des Beaux-Arts de Gand. Liévi...
This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed.Find sources: Image plane – news · newspapers · books · scholar · JSTOR (January 2021) (Learn how and when to remove this message) Three-dimensional (3D)computer graphics Fundamentals Modeling Scanning Rendering Printing Primary uses 3D models Computer-aided design Graphic d...