  We consider a Bayesian method for learning the Bayesian network structure
from complete data. Recently, Koivisto and Sood (2004) presented an algorithm
that for any single edge computes its marginal posterior probability in O(n
2^n) time, where n is the number of attributes; the number of parents per
attribute is bounded by a constant. In this paper we show that the posterior
probabilities for all the n (n - 1) potential edges can be computed in O(n 2^n)
total time. This result is achieved by a forward-backward technique and fast
Moebius transform algorithms, which are of independent interest. The resulting
speedup by a factor of about n^2 allows us to experimentally study the
statistical power of learning moderate-size networks. We report results from a
simulation study that covers data sets with 20 to 10,000 records over 5 to 25
discrete attributes
