  We consider the problem of evaluating designs for a two-arm randomized
experiment with an incidence (binary) outcome under a nonparametric general
response model. Our two main results are that the priori pair matching design
of Greevy et al. (2004) is (1) the optimal design as measured by mean squared
error among all block designs which includes complete randomization. And (2),
this pair-matching design is minimax, i.e. it provides the lowest mean squared
error under an adversarial response model. Theoretical results are supported by
simulations and clinical trial data.
