Competing stimulus assessment

Competition is measured through comparison

A clinician first defines the target response, item contact or engagement, observation unit, scoring rules, conditions, and safety criteria. A no-stimulus control provides a comparison for target behavior without a test stimulus. Each test condition makes one candidate stimulus freely and noncontingently available.

The clinician evaluates target responding and engagement separately. A stimulus can produce high engagement while target behavior continues, or low target behavior with little usable engagement. Both patterns deserve clear reporting.

Preference and competition answer different questions

A preference assessment examines selection or approach among options. A CSA asks how a stimulus relates to target responding when available under the assessment conditions. A highly preferred item may show weak competition, and a lower-ranked item may correlate with stronger reduction.

Ask the person what they enjoy, dislike, or want to try. Direct report and choice support item selection while leaving the observed competition measure intact.

Research supports use with important limits

A systematic review identified 26 CSA applications, with 17 validations meeting the review’s criteria. The authors described the common components as a no-stimulus control, test trials with a stimulus freely available, and measurement of both target behavior and engagement or contact. The literature varied in methods and populations.

Publication samples can overstate routine success. A retrospective consecutive case series reviewed 35 inpatient applications. Using an 80% reduction threshold, 47% of cases identified an effective competing stimulus, compared with over 92% in the authors’ summary of published validations. Different settings and methods limit direct comparison. The contrast warns against promising that every CSA will identify an effective option.

Selection starts with fit and safety

Consider health, allergies, choking risk, sensory effects, durability, sanitation, age, setting, portability, cost, social acceptability as judged by the person, and whether access could interfere with communication or mobility. Obtain interdisciplinary input for medical, feeding, sensory, motor, or communication concerns.

The assessment should never remove essential support to create a comparison. Food, water, bathroom access, AAC, mobility, prescribed care, pain care, and emergency help stay available.

A fictional eight-stimulus example

Suri’s team defines eight candidate stimuli from direct choice, caregiver input, and observation. Each candidate appears in a test condition, and the team includes a no-stimulus control. The observation system records percentage of intervals with target behavior and percentage with contact.

Candidate A shows contact in 8 of 10 intervals and target behavior in 5 of 10. Candidate B shows contact in 6 of 10 and target behavior in 1 of 10. The control contains target behavior in 7 of 10 intervals.

Candidate B shows the strongest observed competition in this small sample, while Candidate A has higher contact. This pattern establishes no durable treatment effect. Replication, client feedback, setting checks, and treatment evaluation still matter. Each denominator stays visible; combining contact and target behavior into one score would hide the tradeoff.

Look beyond an assessment-session winner

An item can lose value, become unavailable, interfere with activities, or work only in one context. Validate candidate stimuli under relevant conditions while preserving safety and the person’s choices. Measure target behavior, engagement, appropriate alternatives, access, side effects, feasibility, and preference over time.

When a candidate has no useful effect, record that outcome. A result of “none identified” can support a better next step, including reassessing function, expanding options, reviewing health variables, or changing the intervention question.

Plan for ordinary use before declaring an option practical. Check whether the person can obtain and operate it, whether partners replenish or maintain it, and whether the option remains available across relevant routines. A bulky clinic item can show competition during assessment and still fail as a community support. Record training, setup time, breakdowns, and the person’s experience.

Keep access voluntary and practical

A competing stimulus is usually available independently of target responding during assessment. Avoid turning it into payment for compliance or withholding it to provoke behavior. If the person declines an item, honor the choice and record the trial outcome.

ASHA’s AAC portal says AAC users should always have access to their communication tools or devices. Never treat a communication system as a competing item to be delivered or removed based on behavior.

The BACB Test Content Outline includes preference assessment, functional assessment, and intervention selection as examination content. The current BACB Ethics Code addresses competence, medical needs, client preferences, consent, assent when applicable, assessment, risk, intervention, data, and evaluation for covered professionals.