A new document has been added to the Society for Political Methodology Website.
Title: The Draw Index: A Measure of Competition for Winner-Take-All Elections
Author(s): Douglas Rose, Douglas Rose
Entry Date: 2010-08-26
Keyword(s): electoral, percentage, outcome, competition, Draw, change, measure, index, tie, winner-take-all, fractionalization, winner, vote, closeness
Abstract: Winner’s percentage, a common measure of electoral competition in winner-take-all elections, measures the shift in vote shares required to produce changes in election outcome. Thus, winner’s percentage of the vote cast is a logical measure of winner-take-all competition. It treats equally shifts from higher to lower ranking candidates. A related measure, the Draw Index, even more clearly measures vote shifting needed to produce tied, then changed outcomes, with weighting by the preceding ties. A final adjustment, yielding the Draw Plus measure, provides a greater emphasis on the importance of a first change in outcome. Across all cases of five or fewer candidates, five measures of competition – including closeness and Rae’s Index of Fractionalization – are highly correlated. Methods of expanding these measures to include non-voters or no preference are explored in an appendix.
http://polmeth.wustl.edu/mediaDetail.php?docId=1252
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