IRSA builds upon
Warren's version of the Single Transferable Vote
method, which has many of the advantages of
Meek's method, while keeping to a minimum the number
of times a ballot is split between candidates.
IRSA differs by preventing votes for winners from ending up in the "exhausted" pile, resulting in higher
winning thresholds and more votes counting for winners than Meek or Warren. IRSA ensures that all
losers are eliminated, so that all votes are assigned to a winner, to the extent possible.
It performs further transfers once all winners are determined so that they have a more equal mandate.
IRSA avoids the use of floating-point math and rounding by giving each voter
a specific number of votes (which can also be represented as fractions of one vote). The combined features make hand counts feasible.
Read an
article (pdf) describing the details and arguments for it.