What is the meaning of "pairwise-randomization"? A special case of stratified randomized experiment, in which a random sample is selected from each group. A special case of clustered randomized experiments, in which a random sample is selected from each group. A special case of stratified randomized experiments, in which each stratum contains exactly two units. A special case of clustered randomized experiments, in which each stratum contains exactly two units. unanswered