Summary: Ma (1996) studied the random order mechanism, a matching mechanism suggested by Roth and Vande Vate (1990) for marriage markets. By means of an example he showed that the random order mechanism does not always reach all stable matchings. Although Ma's (1996) result is true, we show that the probability distribution he presented -and therefore the proof of his Claim 2 -is not correct. The mistake in the calculations by Ma (1996) is due to the fact that even though the example looks very symmetric, some of the calculations are not as "symmetric." JEL classification: C78 For a description of the marriage model we refer to Roth and Vande Vate (1990). A marriage market is denoted by (M, W, P ) where M = {m 1 , . . . , m a } is a set of "men," W = {w 1 , . . . , w a } is a set of "women," and P is a preference profile. The set of stable matchings for (M, W, P ) is denoted by S(P ). We now recall the random order mechanism.
Random Order (RO) MechanismInput: A marriage market (M, W, P ). Set R 0 := ∅, µ 0 such that for all i ∈ N , µ 0 (i) = i, and t := 1.Step t: Choose an agent i t from N \R t−1 at random. Set R t := R t−1 ∪ {i t }. Suppose i t = w ∈ W . (Otherwise replace w by m in Step t.)
Stable Room ProcedureCase (i) There exists no blocking pair (m, w) for µ t−1 with m ∈ R t : Stop if t = n and define RO(P ) := µ t−1 . Otherwise set µ t = µ t−1 and go to Step t := t + 1.
Case (ii)There exists a blocking pair (m, w) for µ t−1 with m ∈ R t : Choose the blocking pair (m * , w) for µ t−1 with m * ∈ R t that w prefers most. If µ t−1 (m * ) = m * , then define µ t such that µ t (w) := m * , µ t (m * ) := w, and for all i ∈ N \{w, m * }, µ t (i) := µ t−1 (i). Stop if t = n and define RO(P ) := µ t . Otherwise go to Step t := t + 1. If µ t−1 (m * ) = w ∈ W , then redefine µ t−1 (w) := m * , µ t−1 (m * ) := w, µ t−1 (w ) := w , and for all i ∈ N \{w, m * , w }, µ t−1 (i) := µ t−1 (i). Set w := w , and repeat the Stable Room Procedure. * We thank two anonymous referees for their helpful comments. B.