Manipulation of variables. The framework for the manipulation of variables during functional analysis is the single-subject design. Two designs are used: the multi-element design (a variation of the alternating treatments design) and the reversal design. The multi-element design allows comparison of conditions in which variables thought to occasion or maintain the behavior are presented. The reversal design is frequently used in conjunction with a multi-element design to confirm a functional relationship between the target behavior and a controlling variable.