The "completely randomised" and the "randomised block" are the only experimental designs suitable for widespread use in pre-clinical research.

Too many pre-clinical experiments are giving results which cannot be reproduced. This may be because the experiments are incorrectly designed. In "Completely randomized" (CR) and "Randomised block" (RB) experimental designs, both the assignment of treatments to experimental subjects and the order in which the experiment is done, are randomly determined. These designs have been used successfully in agricultural and industrial research and in clinical trials for nearly a century without excessive levels of irreproducibility. They must also be used in pre-clinical research if the excessive level of irreproducibility is to be eliminated. A survey of 100 papers involving mice and rats was used to determine whether scientists had used the CR or RB designs. The papers were assigned to three categories "Design acceptable", "Randomised to treatment groups", so of doubtful validity, or "Room for improvement". Only 32 ± 4.7% of the papers fell into the first group, although none of them actually named either the CR or RB design. If the current high level of irreproducibility is to be eliminated, it is essential that scientists engaged in pre-clinical research use "Completely randomised" (CR), "Randomised block" (RB), or one of the more specialised named experimental designs described in textbooks on the subject.