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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