[MrLeRoy]

"In 1992, the minor party vote increased the Bush share of the major party vote by a net 6.4 percentage points by drawing votes that would otherwise have gone to the Democratic candidate; most of the minor party vote, however, would not otherwise have voted. Bush would have lost by an even larger margin in 1992 if not for the minor party vote." - William A. Niskanen, http://www.cato.org/pubs/journal/cj18n1-7.pdf

[Maelstrom]

These studies are ignoring a tremendously huge caveat:

They assume that voters for Perot would still have voted anyway if Perot were not a candidate.