Neutral and Stressful Studies Replacement can be considered under a number of general headings, and admits readily of a general approach.
Reduction is a compact subject, centering on the problem of variance control.
Refinement, the third great path of advance, presents more formidable difficulties to the would-be taxonomist of techniques. It is indeed so protean in its aspects, that it would almost seem to require a separate solution in every single investigation, and refinement might be regarded as an art or an ability to improvise. It is true that the greatest experimenters have been artists in this sense, and that is one reason why we read with such aesthetic pleasure the accounts of their experiments. Nevertheless, the subject of refinement does admit of some generalizations. In this chapter, we shall try to make them.