EXPERIMENTAL DESIGNS OF THE SINGLE-STIMULUS, ALL-OR-NOTHING TYPE.

Experimental designs have previously been treated unsystematically. This article presents all possible experimental designs that use from one to four groups, the groups being differentiated by whether they receive a pretest, a stimulus, neither or both. Pretesting a group on the dependent variable may change the experiment's outcome, as may uncontrolled events. Both factors are worked into the analysis, as well as all possible interactions among these and the stimulus. Contrary to general belief, it develops that the classic two-group design is not optimal, nor are the three-group and four-group designs now in the literature. For every design the investigator must assume a value for one or more quantities, and tables are presented with solutions for unknown quantities under each combination of assumptions. Statistical procedures for data analysis are included. [ABSTRACT FROM AUTHOR]