Almost everywhere domination

AT uring degreea is said to be almost everywhere dominating if, for almost all X 2 2 ! with respect to the \fair coin" probability measure on 2 ! ,a nd for allg : ! ! ! Turing reducible to X ,t here existsf : ! ! ! of Turing degree a which dominates g. We study the problem of characterizing the almost everywhere dominating Turing degrees and other, similarly dened classes of Turing degrees. We relate this problem to some questions in the reverse mathematics of measure theory.