Excerpts from the NYU Department of Politics study by Steven J. Brams, Department of Politics, New York University and Peter C. Fishburn, AT&T Bell Laboratories. (Click here for a detailed analysis of preferential voting systems including STV "multi-seat" elections)
From the preface:
Several alternatives to plurality voting, with and without a runoff, are compared: the Hare system of single transferable vote (STV), the Borda count, cumulative voting, additional-member systems, and approval voting. The Hare system and the Borda count allow voters to rank candidates…
All these voting systems are vulnerable to strategic manipulation. STV is nonmonotonic, which means that a candidate can be hurt when raised in the rankings of some voters,…
Although preferential systems, notably STV, have been used in public elections to ensure proportional representation of different parties in legislatures, the vulnerability of STV to preference truncation illustrates its manipulability, and…casts doubt upon its democratic character. In particular, it seems bizarre that voters can hurt a candidate's chances by raising him or her in their rankings.
(Click the link at the top of this page for the full report)