On Wednesday, TABB Group released its eighth annual U.S. hedge funds benchmark study. In the study, TABB interviewed 63 head traders of U.S.-based hedge funds and asked their top regulatory concerns in the current environment. Overall "regulatory uncertainty" was No. 1, with 35% of responses - up from 29% last year. High-frequency trading was next with 27%, up from 17% last year; while the higher cost of compliance ranked third with 23% of responses, down significantly from 43% in 2012.