The matching of global anomalies of a supersymmetric gauge theory and its
dual is seen to follow from similarities in their classical chiral rings. These
similarities provide a formula for the dimension of the dual gauge group. As
examples we derive 't Hooft consistency conditions for the duals of
supersymmetric QCD and SU(N) theories with matter in the adjoint, and obtain
the dimension of the dual groups.Comment: 9 pages, Revte
