A common problem in applied research is the comparison of treatments with a control or standard. Such a situation may arise, for example, when an agronomist test the effects on crop yield of the addition of chemicals to the soil, or when a pharmacologist assays drug samples to determine their potencies. In designing an experiment to in the experiment a control in the form of either a dummy treatment, to measure the magnitude of the experimental response in the absence of the treatments under investigation, or some recognized standard treatment. Sometimes past experience with the control will suffice, but often this cannot be relied upon due to altered environmental conditions. thus the agronomist may leave a few of his experimental plots untreated for comparison with the treated plots, and the pharmacologist may measure the response concomitantly with the test samples in order to estimate the potencies of the latter.

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