The Hare System of Single Transferable Vote (STV) was first proposed by Thomas Hare in England and Carl George Andrae in Denmark in the l850's. (Thus, claims that this is a "new" system are highly questionable!)

Excerpts from the study by Steven J. Brams Ph.D.,  Department of Politics, New York University and Peter C. Fishburn, AT&T Bell Laboratories. (For a detailed analysis of preferential voting systems including STV "multi-seat" elections, just follow the link in the bottom section of the IRV page.)

It is true that under STV a first choice can never be hurt by ranking a second choice, a second choice by ranking a third choice, etc., because the higher choices are eliminated before the lower choices can affect them.  However, lower choices can affect the order of elimination, and hence the transfer of votes.*

Consequently, a higher choice (e.g., second) can influence whether a lower choice (e.g., third or fourth) is elected. This places voters in a position where they could ultimately HARM their FAVORED CHOICE.

This example illustrates a new and potentially more serious problem with STV (for single seat elections) than its manipulability due to preference truncation, nonmonotonicity!

First, assume that there are four candidates, with 21 voters in the following four ranking groups:

I. 7 voters: abcd

II. 6 voters: bacd

III. 5 voters: cbad

IV. 3 voters: dcba

Because no candidate has a simple majority of q = ll first-place votes, the lowest first-choice candidate, d, is eliminated on the first round, and class IV's 3 second-place votes go to c, giving c 8 votes. Because none of the remaining candidates has a majority at this point, b, with the new lowest total of 6 votes, is eliminated next, and b's second-place votes go to a, who is elected with a total of l3 votes.

Next assume that the 3 class IV voters indicate only d as their first choice. Then d is still eliminated on the first round, but since the class IV voters did not indicate a second choice, no votes are transferred. Now, however, c is the new lowest candidate, with 5 votes; c's elimination results in the transfer of his or her supporters' votes to b, who is elected with ll votes. Because the class IV voters prefer b to a, it is in their interest not to rank candidates below d to induce a better outcome for themselves, again illustrating the truncation problem.

Example 2 illustrates another paradoxical aspect of STV: raising a candidate in one's preference order can actually hurt that candididate. This is referred to as nonmonotonicity (Smith, l973; Doron and Kronick, l977; Fishburn, l982; Bolger, l985). Thus, if the three class IV voters raise a from fourth to first place in their rankings--without changing the ordering of the other three candidates--b is elected rather than a.

This is indeed perverse:

Candidate 'a' loses when he or she moves up in the rankings of some voters and thereby receives more first-place votes. (Also, see EXAMPLE w/THREE candidates!!)

Equally strange, candidates may be helped under STV if voters do not show up to vote for them at all, which has been called the "no-show paradox" (Fishburn and Brams, l983; Moulin, l986; Ray, l986; Holzman, l987).