The Brits like to weigh the fruits of academic labor more than we do on this side of the water. Or, at least it seems that way to me. The Research Assessment Exercise and now the Research Excellence Framework indicate as much. According to a March 2 update in the Chronicle: "Government-backed academic research in Britain will for the first time be assessed and financed based in part on its societal and economic impact, although the weight given to such measures will be slightly less than originally, and controversially, proposed. The agencies responsible for financing research announced on Tuesday that such impact will account for 20 percent and not 25 percent, as originally proposed, in the 2014 Research Excellence Framework." (See more on that here: Anthea Lipsett, "Universities braced for heavier research burden," Guardian, March 1, 2011.)
Somehow, I missed this list of "Top 20 Journals in History" from Times Higher Education, posted back in January. Thomson Reuters, a Canadian information company, first published the list in its Journal Citation Reports (2009). "Impact factors are short-term measures of the average influence of journal publications," reports THE. "They were devised to help librarians understand, for a specific field, which publications exhibited the greatest influence, as measured by citations per paper. These statistics were intended to aid decisions about which serials to acquire."
(See more on how this is compiled and see more of the list here.)