Professor David Sibley was retained by the DOJ to perform an evaluation of the competitive effects of the proposed merger of AT&T and T-Mobile. A Competition Economics case team, led by Director Michael Doane, assisted Professor Sibley in his analysis. The proposed merger would have brought together the second and fourth largest telecommunications carriers in the United States. AT&T announced on December 19, 2011 that it would no longer pursue its $39 billion attempt to purchase T-Mobile.