TABLE 2.

Summary of single-subject experimental designs (SSEDs).

Design	Research questions	Advantages	Disadvantages
Pre-experimental (AB)	Does outcome X change from baseline levels with the introduction of intervention B?	• Quick and efficient to implement. • Appropriate for low-stakes decision making.	• Does not control for threats to internal validity; not an experimental design.
Withdrawal (ABA/ABAB)	Does outcome X covary with introduction and withdrawal of intervention B?	• Easy to implement, strong experimental control when effects are immediate and large.	• There are ethical considerations regarding withdrawing or reversing a potentially effective intervention. • Not all behaviors are “reversible.”
Multiple-baseline/multiple-probe	Does outcome X change from baseline levels with the introduction of intervention B over multiple participants, responses, settings, etc.?	• Does not require withdrawal of intervention. • Appropriate for nonreversible behaviors.	• Ethical considerations regarding keeping individuals/behaviors in baseline conditions for a long period. • Requires multiple individuals, responses, settings, etc., that are comparable in order to replicate effects.
Changing-criterion	Do changes in the level of outcome X correspond to changes in the intervention criteria?	• Does not require reversal. • Appropriate for behaviors that can be changed gradually. • Useful for consequence-based interventions.	• Change must take place in graduated steps; not appropriate for behaviors that require immediate change. • Requires the use of incentive- or consequence-based interventions.
Multiple-treatment	What are the relative effects of interventions A and B (and C, D, etc.) on outcome X compared to each other and/or baseline levels?	• Can be extended to compare any number of interventions or variables. • Can extend a withdrawal study when effects of initial intervention are not as pronounced as expected. • Can be used to conduct component analyses of necessary and sufficient intervention components.	• Behaviors should be reversible to demonstrate relative effects. • Only comparisons between adjacent conditions are appropriate. • Can be time consuming and complicated to implement when the number of interventions being compared increases. • Results are susceptible to multiple treatment interference.
Alternating treatments	What are the relative effects of interventions A and B (and C, D, etc.) on outcome X compared with each other and/or baseline levels?	• Can be extended to compare any number of interventions or variables. • Can provide strong experimental evidence in relatively few sessions.	• Behaviors must be readily reversible to obtain differentiation between conditions. • Results are susceptible to multiple treatment interference.
Adapted alternating treatments	What are the relative effects of intervention A on outcome X and intervention B on outcome Y?	• Less prone to multiple treatment interference. • Can provide strong experimental evidence in relatively few sessions. • Does not require reversal.	• Set of behaviors or stimuli must be directly comparable for effects to be meaningful. • Potential generalization across behaviors must be considered.