Knowledge (XXG)

McKelvey–Schofield chaos theorem

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shows that when preferences are restricted to be single-peaked on the real line, Arrow's theorem does not hold, and the median voter's ideal point is a Condorcet winner. The chaos theorem shows that this good news does not continue in multiple dimensions.
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of policies, where each policy further along the path would win against one earlier. Some of Schofield's proofs were later found to be incorrect by Jeffrey S. Banks, who corrected his proofs.
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of two voters indifference curves would beat it. Any point in the plane will almost always have a set of points that are preferred by 2 out of 3 voters.
689: 614: 27:. It states that if preferences are defined over a multidimensional policy space, then majority rule is in general unstable: there is no 129: 331:
McKelvey proved that elections can be even more "chaotic" than that: If there is no equilibrium outcome then any two policies, e.g.
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McKelvey, Richard D. (June 1976). "Intransitivities in Multidimensional Voting Models and Some Implications for Agenda Control".
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considered the case when preferences are "Euclidean metrics". That means every voter's utility function has the form
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extended the theorem to more general classes of utility functions, requiring only that they are
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Under these conditions, there could be a collection of policies which don't have a
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centered at the preferred policy. If a policy was proposed, then any policy in
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Disposing dictators, demystifying voting paradoxes: social choice analysis
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Schofield, N. (1 October 1978). "Instability of Simple Dynamic Games".
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using majority rule. This means that, given a number of policies
632:"Singularity theory and core existence in the spatial model" 88:, who vote for policies which are represented as points in 115:, which measures how much they value different policies. 734: 281:, there could be a series of pairwise elections where: 345: 228: 132: 48: 396: 241: 196:{\displaystyle U_{i}(x)=\Phi _{i}\cdot d(x,x_{i})} 195: 63: 84:The theorem considers a finite number of voters, 674:(2008). "Deliver Us from the Plurality Vote". 34:The theorem can be thought of as showing that 754: 8: 38:holds when preferences are restricted to be 761: 747: 96:. Each vote is between two policies using 647: 388: 363: 350: 344: 233: 227: 184: 159: 137: 131: 55: 51: 50: 47: 479:The simplest illustrating example is in 528: 607:Positive Changes in Political Science 397:{\displaystyle X_{1},X_{2},...,X_{s}} 7: 715: 713: 451:This is true regardless of whether 733:. You can help Knowledge (XXG) by 230: 156: 14: 636:Journal of Mathematical Economics 717: 630:Banks, Jeffrey S. (1995-01-01). 475:An example of McKelvey's theorem 64:{\displaystyle \mathbb {R} ^{n}} 21:McKelvey–Schofield chaos theorem 339:, have a sequence of policies, 565:The Review of Economic Studies 190: 171: 149: 143: 16:Result in social choice theory 1: 36:Arrow's impossibility theorem 649:10.1016/0304-4068(94)00704-E 550:10.1016/0022-0531(76)90040-5 801: 712: 682:Cambridge University Press 538:Journal of Economic Theory 242:{\displaystyle \Phi _{i}} 785:Economic theories stubs 680:. Cambridge, New York: 476: 398: 243: 197: 65: 729:related article is a 474: 399: 244: 198: 119:Euclidean preferences 66: 780:Social choice theory 343: 226: 130: 73:median voter theorem 46: 25:social choice theory 603:Shepsle, Kenneth A. 251:monotone decreasing 485:indifference curve 477: 394: 239: 220:Euclidean distance 193: 61: 742: 741: 691:978-0-521-51605-1 616:978-0-472-06986-6 203:for all policies 792: 763: 756: 749: 721: 714: 704: 703: 672:Saari, Donald G. 668: 662: 661: 651: 627: 621: 620: 595: 589: 588: 560: 554: 553: 533: 503:Norman Schofield 489:the intersection 458: 454: 447: 443: 432: 425: 417: 410: 403: 401: 400: 395: 393: 392: 368: 367: 355: 354: 338: 334: 327: 320: 312: 305: 297: 290: 280: 273: 266: 258:Condorcet winner 248: 246: 245: 240: 238: 237: 217: 213: 206: 202: 200: 199: 194: 189: 188: 164: 163: 142: 141: 124:Richard McKelvey 114: 106:utility function 103: 95: 87: 70: 68: 67: 62: 60: 59: 54: 29:Condorcet winner 800: 799: 795: 794: 793: 791: 790: 789: 770: 769: 768: 767: 727:economic theory 710: 708: 707: 692: 670: 669: 665: 629: 628: 624: 617: 597: 596: 592: 577:10.2307/2297259 562: 561: 557: 535: 534: 530: 525: 519: 516: 511:continuous path 500: 498:Generalisations 494: 469: 456: 452: 445: 442: 438: 431: 427: 424: 420: 416: 412: 408: 384: 359: 346: 341: 340: 336: 332: 326: 322: 319: 315: 311: 307: 304: 300: 296: 292: 289: 285: 279: 275: 272: 268: 265: 261: 229: 224: 223: 215: 212: 208: 204: 180: 155: 133: 128: 127: 121: 113: 109: 101: 93: 90:Euclidean space 85: 82: 49: 44: 43: 23:is a result in 17: 12: 11: 5: 798: 796: 788: 787: 782: 772: 771: 766: 765: 758: 751: 743: 740: 739: 722: 706: 705: 690: 663: 642:(6): 523–536. 622: 615: 590: 571:(3): 575–594. 555: 544:(3): 472–482. 527: 526: 524: 521: 507:differentiable 499: 496: 481:two dimensions 468: 465: 449: 448: 440: 436: 433: 429: 422: 418: 414: 391: 387: 383: 380: 377: 374: 371: 366: 362: 358: 353: 349: 329: 328: 324: 317: 313: 309: 302: 298: 294: 287: 277: 270: 263: 236: 232: 210: 192: 187: 183: 179: 176: 173: 170: 167: 162: 158: 154: 151: 148: 145: 140: 136: 120: 117: 111: 100:. Each voter, 81: 78: 58: 53: 15: 13: 10: 9: 6: 4: 3: 2: 797: 786: 783: 781: 778: 777: 775: 764: 759: 757: 752: 750: 745: 744: 738: 736: 732: 728: 723: 720: 716: 711: 701: 697: 693: 687: 683: 679: 678: 673: 667: 664: 659: 655: 650: 645: 641: 637: 633: 626: 623: 618: 612: 608: 604: 600: 594: 591: 586: 582: 578: 574: 570: 566: 559: 556: 551: 547: 543: 539: 532: 529: 522: 520: 517: 514: 512: 508: 504: 497: 495: 492: 490: 486: 482: 473: 466: 464: 462: 437: 434: 419: 407: 406: 405: 389: 385: 381: 378: 375: 372: 369: 364: 360: 356: 351: 347: 314: 299: 284: 283: 282: 259: 254: 252: 234: 221: 185: 181: 177: 174: 168: 165: 160: 152: 146: 138: 134: 125: 118: 116: 107: 99: 98:majority rule 92:of dimension 91: 79: 77: 74: 56: 41: 37: 32: 30: 26: 22: 735:expanding it 724: 709: 676: 666: 639: 635: 625: 606: 599:Cox, Gary W. 593: 568: 564: 558: 541: 537: 531: 518: 515: 501: 493: 478: 460: 450: 330: 255: 122: 83: 33: 20: 18: 455:would beat 80:Definitions 774:Categories 523:References 461:vice versa 444:wins over 426:wins over 411:wins over 321:wins over 306:wins over 291:wins over 253:function. 700:227031682 658:0304-4068 231:Φ 207:and some 166:⋅ 157:Φ 214:, where 104:, has a 585:2297259 467:Example 218:is the 40:concave 698:  688:  656:  613:  583:  71:. 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Index

social choice theory
Condorcet winner
Arrow's impossibility theorem
concave
median voter theorem
Euclidean space
majority rule
utility function
Richard McKelvey
Euclidean distance
monotone decreasing
Condorcet winner

two dimensions
indifference curve
the intersection
Norman Schofield
differentiable
continuous path
doi
10.1016/0022-0531(76)90040-5
doi
10.2307/2297259
JSTOR
2297259
Cox, Gary W.
Shepsle, Kenneth A.
ISBN
978-0-472-06986-6
"Singularity theory and core existence in the spatial model"

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