A completely randomized design (CRD) is the simplest design for comparative experiments, as it uses only two basic principles of experimental designs: randomization and replication. Its power is best understood in the context of agricultural experiments (for which it was initially developed), and it will be discussed from that perspective, but true experimental designs, where feasible, are useful in the social sciences and in medical experiments.

In CRDs, the treatments are allocated to the experimental units or plots in a completely random manner. CRD may be used for single- or multifactor experiments. This entry discusses the application, advantages, and disadvantages of CRD studies and the processes of conducting and analyzing them.