HOW TO BE INCOHERENT AND SEDUCTIVE - BOOKMAKERS ODDS AND SUPPORT THEORY

Support theory (Tversky and Koehler, 1994) implies that different desc riptions of the same event can prompt different subjective probabiliti es, More explicit descriptions are assumed to enable retrieval of stro nger evidence prompting a higher subjective likelihood, In this paper bookmakers' odds are examined in relation to this hypothesis, British bookmakers quote odds for victory, draw, or loss for football teams an d also for more specific components such as the actual score of the ga me, Consistent with support theory, bookmakers' odds for general hypot heses are subadditive; they are smaller than the sum of the odds given to an explicitly unpacked, but extensionally equivalent, disjunction of events subsumed by the general hypothesis, The extent of the subadd itivity increases for hypotheses unpacked into a larger number of comp onents, However, although support theory implies that probabilities fo r explicitly presented disjunctions of events should be additive, the sum of the odds given to race horses increases with the number of hors es in the race, These findings are discussed in relation to other evid ence for non-additivity. (C) 1997 Academic Press.