In the context of voting, if party A’s share of the vote falls by a% and party B’s share of the vote rises by b%, then, according to one definition, the swing from A to B is ½(a+b)%. An alternative measure uses percentages of the total vote for parties A and B (so that the swing is a%=b%). When there are three major parties, however, neither definition is entirely satisfactory, since the majority vote can pass from party A to party B, while both parties are losing votes to party C.