The ancient black art and transdisciplinary extent of pseudoreplication.

The history, definitions, and transdisciplinary extent of pseudoreplication, as well as some key concepts of experimental design, are briefly reviewed. Pseudoreplication, sometimes also referred to as the 'unit of analysis error,' is one of the commonest errors of statistical analysis and interpretation. It is a simple albeit serious one. It persists in part because of the failure of statisticians and scientists to develop a clear, consistent terminology for the concepts of statistics, experimental design, and sampling design that is used across all disciplines, as well as a terminology for specific categories of the more common errors. Lack of a clear terminology, in turn, has fostered narrow, discipline-specific jargon, inconsistency among textbooks and reference works, and ineffective teaching. Reform of terminology is possible, and great improvement in statistical practice would follow.