A study is made of the three most popular counter-based compaction schemes, i.e., one's counting, transition counting, and edge counting. For one's counting, using the asymmetric error model, equations for iterative computations of exact aliasing probability for any test session length are derived, and the asymptotic probability of aliasing is determined. Also presented is a closed form expression that, for any test session length, gives the exact aliasing probability. Some examples that compare the aliasing by counter-based compaction with that by linear feedback shift registers are presented.ETX