Fundamentals of Experimental Design: What the Textbooks Don't Necessarily Tell You.

We often think of experimental designs as analogous to recipes in a cookbook.  We look for something that we like and frequently return to those that have become our long-standing favorites.  We can easily become complacent, favoring the tried-and-true designs (or recipes) over those that contain unknown or untried ingredients or those that are simply too weird for our tastes.  Instead, I prefer to think of experimental designs as a creative series of decisions that are meant to solve one or more problems.  These problems may be real or imagined - we may have direct evidence of a past or current problem or we may simply want insurance against future potential problems.  The most significant manifestation of a "problem" is unsatisfactory p-values that prevent us from developing inferences about treatment differences.  Six tenets of experimental design - randomization, degree of replication, form of replication, size of experimental unit, level of blocking, and size/shape of blocks - can be used creatively, intelligently, and consciously to solve both real and perceived problems in comparative experiments.