  Our world is filled with both beautiful and brainy people, but how often does
a Nobel Prize winner also wins a beauty pageant? Let us assume that someone who
is both very beautiful and very smart is more rare than what we would expect
from the combination of the number of beautiful and brainy people. Of course
there will still always be some individuals that defy this stereotype; these
beautiful brainy people are exactly the class of anomaly we focus on in this
paper. They do not posses intrinsically rare qualities, it is the unexpected
combination of factors that makes them stand out.
  In this paper we define the above described class of anomaly and propose a
method to quickly identify them in transaction data. Further, as we take a
pattern set based approach, our method readily explains why a transaction is
anomalous. The effectiveness of our method is thoroughly verified with a wide
range of experiments on both real world and synthetic data.
