One cannot make a “concerted effort” all by one’s self. To work “in concert” is to work together with others. One can, however, make a concentrated effort. The prefix “con-” means “with.”
Sparring S.African mine unions sit down for talks PRETORIA (Reuters) - Senior South African ministers, mining bosses and union leaders met on Friday in the most concerted effort yet to end 18 months of labour strife and violence that has hit growth in Africa's biggest economy. Critically, leaders of both the National Union of Mineworkers (NUM), an ally of the ruling African National Congress, and rival Association of Mineworkers and ...
June 14, 2013 - Reuters via Yahoo! News