This ranking is across all fields, and is based mostly on survey results.
BU rankings in various subsets by USN&WR are linked here.
In Economics, BU was only ranked #24 by USN&WR, tied with Johns Hopkins, and just behind Brown, CMU, Duke, Maryland, Rochester.
This lower than hoped ratings of the department is not so surprising if you look at the USN&WR methodology:
“Rankings of doctoral programs in the social sciences and humanities are based solely on the results of peer assessment surveys sent to academics in each discipline.”
Peer assessments tend to change very slowly over time and our image before 2000 still enters into peoples ranking.
Economics had a 25 percent response rate from the department heads and directors of Graduate studies to whom they sent questionnaires.
BU tends to do better when using citations (currently ranked 12 by REPEC in the US behind Yale, Brown and Michigan, but ahead of U. Penn)
Another ranking is by QS World Universities where we are ranked 18 in the US 47th in the world, just behind Duke, Michigan, UCSD and Brown.
“The rankings highlight the world’s top universities in 36 individual subjects, based on academic reputation, employer reputation and research impact (full methodology here)”
The AEA own list of rankings, features several older ones.