Optimal Design in Psychological Research

Psychologists often do not consider the optimality of their research designs. However, increasing costs of using inefficient designs requires psychologists to adopt more efficient designs and to use more powerful analysis strategies. Common designs with many factor levels and equal allocations of observations are often inefficient for the specific questions most psychologists want to answer. Happenstance allocations determined by random sampling are usually even more inefficient and some common analysis strategies can exacerbate the inefficiency. By selecting treatment levels and allocating observations optimally, psychologists can greatly increase the efficiency and statistical power of their research designs. A few heuristic design principles can produce much more efficient designs than are often used.