By Matt Harrington, BCBA · Behaviorist Book Club · April 2026 · 12 min read

Competing Stimulus Assessments: Clinical Applications and Recent Advances in ABA Practice

Overview & Clinical Significance

Competing Stimulus Assessments (CSAs) represent one of the most clinically practical pretreatment tools available to behavior analysts working with challenging behavior. Originally developed from preference assessment methodology, the CSA was designed to identify specific stimuli capable of reducing the frequency or severity of challenging behavior — not through direct suppression, but through reinforcer competition. When a sufficiently potent alternative reinforcer is freely available, engagement with that reinforcer can functionally displace the challenging behavior.

Louis Hagopian's presentation, delivered in a podcast-style interview format, provides a comprehensive update on CSA methodology, including how the assessment evolved, how it differs from traditional preference assessments, and what recent findings reveal about augmenting CSA procedures to improve outcomes. For BCBAs designing function-based treatment for self-injurious behavior, stereotypy, or other persistent challenging behaviors, the CSA provides a systematic, pre-intervention method for identifying naturalistic intervention components that can reduce treatment intensity, improve social validity, and accelerate clinical progress.

The CSA is particularly relevant in cases where functional communication training, extinction, or other first-line interventions have not achieved full suppression of challenging behavior, or where treatment practicality in natural environments is limited. Understanding how to conduct, interpret, and augment CSAs is a meaningful addition to any behavior analyst's clinical toolkit.

Background & Context

The Competing Stimulus Assessment grew from the preference assessment literature, which itself developed from foundational work on reinforcer identification in ABA. Stimulus preference assessments — including the paired-stimulus (PS) format and multiple-stimulus without replacement (MSWO) format — identify which stimuli an individual tends to select or engage with most when given a choice. These assessments predict relative reinforcer value but do not directly test whether the stimulus will compete with the motivation underlying challenging behavior.

The CSA extends this logic by presenting candidate stimuli during a period when challenging behavior might otherwise occur and measuring whether engagement with each stimulus is associated with reductions in the challenging behavior. The key innovation is the focus on reinforcer competition: not just 'what does this person prefer?' but 'what does this person prefer enough to choose over the activity reinforcing the challenging behavior?' This distinction has important treatment implications.

From a motivating operations (MO) perspective, CSAs test the interaction between the MO for challenging behavior and the availability of alternative reinforcement. When the MO for the challenging behavior is strong (e.g., high levels of EO for attention or escape), fewer stimuli will successfully compete. When the MO is weaker, a wider range of stimuli may produce competition effects. This MO-sensitivity of CSA outcomes has practical implications for when assessments should be conducted and how results should be interpreted.

Hagopian's work and the broader CSA literature have examined applications to self-injurious behavior, stereotypy, and other maintained challenging behaviors across a wide range of populations, expanding what was initially a fairly narrow assessment procedure into a versatile pretreatment toolkit.

Clinical Implications

The CSA has direct clinical utility across several intervention domains. Most fundamentally, high-competition stimuli identified through the CSA can be incorporated into treatment plans as non-contingent reinforcement (NCR) components. Providing a highly preferred, highly competing stimulus on a fixed-time or variable-time schedule can reduce the motivating operation for the challenging behavior and create behavioral momentum for appropriate engagement — without requiring the full infrastructure of a comprehensive behavioral intervention.

For BCBAs who supervise treatment in settings where caregiver training is intensive and complex interventions are difficult to implement with fidelity, CSA-identified competing stimuli offer a practical, lower-burden first-line option. A caregiver who can reliably provide access to a specific sensory toy during transition times may be able to implement this NCR component even before more complex DRO or FCT procedures are fully trained.

The CSA also informs the selection of alternative activities for leisure skill development. If the assessment identifies that engagement with specific leisure materials reliably competes with challenging behavior, those materials are strong candidates for structured leisure instruction. Building a rich, independent leisure repertoire is a high-value clinical goal that simultaneously addresses quality of life and reduces the motivational context for challenging behavior.

Recent augmenting tactics described in Hagopian's work — such as embedding brief response prompts, pairing stimuli with additional reinforcer dimensions, or manipulating the temporal parameters of stimulus access — provide clinicians with tools to enhance competition effects for stimuli that show moderate but not complete suppression in their baseline CSA form. Understanding these augmentation strategies expands the number of viable competing stimuli available for treatment.

Ethical Considerations

The BACB Ethics Code has direct relevance to the use of CSAs and CSA-informed interventions. Code 2.14 (Selecting, Designing, and Implementing Behavior-Change Interventions) requires that behavior analysts select interventions based on the best available scientific evidence and the individual needs of the client. CSAs represent a pretreatment assessment that meets this standard — they are empirically derived, individualized to the client, and directly inform treatment selection.

Code 2.15 addresses the use of least restrictive effective interventions. CSA-guided approaches exemplify this principle: by identifying naturally occurring stimuli that compete with challenging behavior, the clinician gains access to reinforcement-based alternatives that may reduce or eliminate the need for more restrictive components such as planned ignoring, response blocking, or punishment procedures. Conducting a CSA before defaulting to more restrictive alternatives is consistent with both evidence-based practice and ethical service delivery.

Code 2.18 (Discontinuing Services) and ongoing assessment obligations mean that CSA results should be monitored longitudinally. Competing stimulus efficacy may change as the individual's learning history, motivating operations, and repertoire evolve. A stimulus that competed effectively early in treatment may lose its competition value as habituation occurs or as the individual's overall reinforcer landscape shifts. Regular re-assessment and updating of CSA-informed intervention components is both clinically appropriate and ethically indicated.

Informed consent (Code 3.04) applies to the conduct of the CSA itself. Caregivers and, where appropriate, clients should understand what the assessment involves, what information it will yield, and how that information will inform treatment planning.

Assessment & Decision-Making

Conducting a high-quality CSA requires several decisions before the assessment begins. First, the set of candidate stimuli must be identified. Typically this involves a preference assessment to generate a pool of high-preference items, from which a subset is selected for CSA testing. The goal is to identify stimuli with sufficiently diverse sensory properties to maximize the likelihood that some will compete with the specific reinforcer maintaining the challenging behavior.

The CSA itself involves presenting each candidate stimulus, one at a time, during a fixed-duration session and recording both time engaged with the stimulus and rate of challenging behavior. A control condition (no stimulus present) provides the baseline against which competition is evaluated. Stimuli are ranked by the degree to which their presence is associated with reductions in challenging behavior and increases in engagement.

Interpreting CSA results requires considering both dimensions: it is possible for a stimulus to show high engagement without producing challenging behavior reductions (if the challenging behavior and the engagement are not functionally incompatible), or to show challenging behavior reductions with low engagement (potentially reflecting an NCR mechanism beyond simple reinforcer competition). High-competition stimuli ideally show both high engagement and challenging behavior reductions relative to the control condition.

Decision-making following the CSA involves selecting which competing stimuli to incorporate into treatment, determining the format of stimulus delivery (NCR schedule, contingent access, structured leisure instruction), and specifying how competition effects will be monitored in ongoing treatment data. The CSA should be repeated periodically and whenever treatment outcomes plateau or challenging behavior resurges.

What This Means for Your Practice

Behavior analysts who add the CSA to their pretreatment assessment repertoire gain a tool that strengthens the ecological validity and practical feasibility of their treatment plans. Several practice-level takeaways follow from this course.

First, conduct CSAs before finalizing treatment plans for persistent challenging behavior. The information gained — particularly about which stimuli produce reliable competition effects — directly informs NCR component selection, leisure skill programming, and the sequencing of intervention elements. This is not an optional add-on; it is a meaningful piece of the functional assessment puzzle that informs treatment selection in ways that preference assessments alone cannot.

Second, treat CSA results as dynamic rather than static. Competing stimulus efficacy changes over time, and a stimulus that worked six months ago may not work as well today. Build CSA re-assessment into your treatment monitoring schedule, particularly for clients with chronic challenging behavior or complex reinforcement histories.

Third, explore augmentation tactics when initial CSA results show partial competition. Hagopian's work on augmenting the CSA demonstrates that moderate competition stimuli can often be enhanced through procedural modifications. Before concluding that a stimulus does not have clinical utility, consider whether augmentation strategies might increase its competition value.

Finally, communicate CSA findings to caregivers in accessible terms. Explaining that you identified specific activities that the individual finds engaging enough to displace the challenging behavior — and that you will use these as part of treatment — gives caregivers a concrete, positive understanding of one element of the intervention. This kind of communication supports buy-in, implementation fidelity, and the collaborative relationship that is essential to treatment success.