Covariate adjustment in randomization-based causal inference for 2K   factorial designs
  We develop finite-population asymptotic theory for covariate adjustment in randomization-based causal inference for 2K factorial designs. In particular, we confirm that both the unadjusted and covariate-adjusted estimators of the factorial effects are asymptotically normal, and the latter is more precise than the former. 
Jiannan Lu
stat.ME