On Wed, 24 Oct 2001, Bart Ingles wrote: > It seems to me that any time strategic (i.e. polling) information is > potentially useful, the election can be manipulated by supplying > inaccurate polling data.
True. > Checking for a beatsall winner doesn't prevent this. I would agree with this statement if you modified it to say,"Even checking for a beats-all winner rarely prevents this completely." Consider the case of a beats-all check followed by your random ballot suggestion: Voters are to submit ranked ballots with truncations allowed internally as well as at the extremes (i.e. where there is no preference equal ranks are allowed). Suppose that the winner of the election is to be the beats-all candidate if there is one, and otherwise the highest ranked candidate on a randomly drawn ballot. How would polling information make any difference in the way anybody voted? After the election, no matter who the winner turned out to be, and no matter how all of the other voters actually voted, how could any sincere voter regret his/her voted ballot? So beats-all with random completion is strategy free and non-manipulable. If some other completion is used, then the election can be manipulated to some degree, depending on the completion method. It seems to me that the beats-all check on the front end of the method can soften the effect of strategy mistakes on the back end "completion" as long as the completion method isn't too blatantly prone to order reversal strategy like Borda. Suppose that Approval is the completion method, for example. It takes polling information for voters to make a good choice of approval cutoff, but no polling information to decide on the order of the candidates. If the polling information is totally wrong, the approval cutoff choices may be bad, but with a little bit of luck, the election is decided before the approval stage. To minimize the potential for manipulation, Condorcet with Approval Completion would be carried out with two trips to the polls. If there is a CW, only one trip is necessary. If not, then the results of the first trip reliably inform the choices for the second (Approval) trip to the polls. Of course (as Demorep is sure to point out) this method is too complicated and inconvenient for public consumption, but it may have private application in situations where it is important to minimize the potential for manipulation. More importantly, as far as I'm concerned, it helps us see the practical limitations of strategy free methods. Forest
