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

Formal Preference Assessments vs. In-the-Moment Reinforcer Analysis for Individuals with ASD

Overview & Clinical Significance

Preference assessments are a cornerstone of effective behavioral intervention for individuals with autism spectrum disorder. Before any reinforcement-based treatment can be implemented with integrity, clinicians must identify stimuli that function as reinforcers for each individual client. Without that empirical foundation, intervention programs risk relying on assumed preferences that may not actually motivate behavior change, undermining both efficiency and client outcomes.

Formal preference assessments — particularly the paired stimulus (PS) format — have accumulated substantial empirical support since their development in the early 1990s. They are now considered standard practice and are conducted multiple times per day in many ABA programs. The rationale is sound: reinforcer value shifts over time due to satiation, motivating operations, and changing developmental interests, so frequent reassessment helps clinicians stay aligned with what is currently reinforcing for a given client.

However, the time cost of formal preference assessments is a genuine clinical concern. In busy ABA settings, every minute spent on assessment is a minute not spent on direct instruction or other therapeutic activities. Pair that with the documented burden on practitioners working with clients who have limited tolerance for prolonged assessment sessions, and the question becomes practical: is there a more efficient approach that preserves assessment quality?

In-the-moment reinforcer analysis (IMA) addresses this gap directly. Rather than conducting a separate assessment phase before intervention, IMA embeds reinforcer identification within the task itself. Clinicians present potential reinforcers during an instructional activity and observe approach, engagement, and consumption behaviors in real time. The result is a procedure that is simultaneously less time-intensive and ecologically valid — the reinforcer is evaluated in the context in which it will actually be used.

This course, presented by Dr. Leaf, centers on a study comparing response rates during a sorting task when reinforcers were identified via the paired stimulus format versus in-the-moment analysis. The findings have direct implications for how BCBAs allocate assessment time, structure session schedules, and evaluate the practical utility of different preference assessment formats.

Background & Context

Preference assessment methodology has evolved considerably since the foundational work published in the Journal of Applied Behavior Analysis in the late 1980s and early 1990s. Early approaches relied on asking caregivers about client preferences — a method that has since been shown to produce inaccurate rankings relative to what clients actually approach and consume. This spurred the development of more objective, observation-based formats.

The most widely studied formats include: free operant observation, single stimulus presentation, paired stimulus (PS), and multiple stimulus formats (with and without replacement). Each has tradeoffs in terms of time required, accuracy of the hierarchy produced, and feasibility for clients with challenging behavior or limited attention. The paired stimulus format, also known as the forced-choice format, involves presenting two items simultaneously and recording which the client approaches. Over successive trials, every item is paired with every other item, producing a relative preference hierarchy.

Behavior analysts are trained to conduct these assessments regularly because reinforcer efficacy is not stable. A stimulus that functions as a powerful reinforcer in the morning session may have diminished value by the afternoon due to satiation. This is why multiple daily assessments have become common in intensive early intervention programs. The BACB Task List and ethics guidance reinforce that reinforcer identification is an ongoing clinical responsibility, not a one-time activity at intake.

The problem is that conducting multiple formal assessments per day can consume a substantial proportion of total session time, particularly when working with clients who have restricted interests, require physical prompting to engage in assessment trials, or display problem behavior during transitions between preferred items. These practical constraints have motivated researchers to examine whether abbreviated or embedded alternatives can produce equivalent or comparable outcomes.

In-the-moment reinforcer analysis draws on ecological validity by assessing preference within the actual activity context. When a clinician presents a task and observes which offered item the client engages with most, they are measuring reinforcer function under the conditions that matter — not under the artificial conditions of a discrete preference assessment trial. This approach aligns with naturalistic teaching frameworks and may be particularly relevant for practitioners working within play-based or incidental teaching models.

Clinical Implications

The core clinical question raised by this course is whether rates of responding during instruction differ based on whether reinforcers were identified via paired stimulus assessment or in-the-moment analysis. If the two approaches yield comparable responding, practitioners have evidence to support a more flexible, time-efficient approach to reinforcer identification in certain contexts.

For BCBAs overseeing intensive programs, the scheduling implications alone are significant. If IMA can substitute for a full paired stimulus assessment in specific conditions — such as tasks with known histories of reinforcement or for clients with stable, well-documented preference hierarchies — session time can be reallocated to direct instruction, generalization probes, or caregiver training.

However, the clinical picture is rarely this clean. Certain clients may show greater variability in preference when assessed in-the-moment versus under structured conditions. Clients with limited behavioral repertoires, restricted interests, or communication impairments may not clearly signal preference through approach behavior during a task, making in-the-moment analysis more difficult to interpret reliably. BCBAs must consider individual client characteristics when deciding which format to use.

Additionally, documentation requirements must be considered. The BACB Ethics Code 2.13 requires that behavior analysts use assessment results to inform behavior change programs. When IMA is the method used, BCBAs should have a clear, replicable procedure for how reinforcers are identified and selected so that the approach meets the standard of systematic assessment rather than ad hoc reinforcer selection.

Practical training implications also deserve attention. Registered Behavior Technicians conducting direct therapy need clear guidance on what IMA looks like in practice — how to present options, how to read approach indicators, and when to flag that a client's reinforcer may have lost its value mid-session. This requires explicit training protocols rather than vague instruction to "watch for what the client likes."

Finally, BCBAs should consider using IMA alongside, rather than exclusively replacing, periodic formal assessments. The two approaches may serve complementary functions: formal assessments provide a structured hierarchy for program planning, while IMA offers real-time adjustment during sessions.

Ethical Considerations

Ethics Code 2.01 (Providing Effective Treatment) requires that behavior analysts use scientifically supported methods. When a BCBA chooses a preference assessment format, that choice carries an ethical weight: an inadequate assessment can result in ineffective or nonexistent reinforcement, which directly undermines the client's right to receive effective intervention.

Code 2.09 (Treatment/Intervention Efficacy) further requires that behavior analysts evaluate the effectiveness of their interventions. If a clinician is using IMA and response rates drop, this is a measurable signal that the identified reinforcer may not be functioning effectively. BCBAs are obligated to respond to that data — not to persist with an approach that is producing poor outcomes because it is more convenient.

Code 2.04 (Accepting Clients) and broader competence requirements under Code 1.05 (Competence) apply when BCBAs adopt new assessment procedures. If a practitioner intends to use IMA, they should have adequate training and procedural knowledge to implement it consistently. Simply abandoning formal preference assessments in favor of a less-structured approach without procedural guidance does not meet the standard of competent practice.

Caregiver and stakeholder involvement is another ethical dimension. Code 2.10 (Involving Clients and Stakeholders) supports the inclusion of family preferences in treatment decisions. Some caregivers may have strong opinions about how reinforcers are selected, particularly if they observe sessions and notice that no formal assessment occurred prior to the start of instruction. BCBAs should proactively discuss assessment procedures and their rationale with families.

There is also a systemic ethics consideration. In organizations serving many clients across multiple programs, policy decisions about which assessment format to use have population-level effects. BCBAs in supervisory or clinical director roles have a responsibility under Code 4.0 series (Responsibility to the Science) to ground organizational policies in data — and that includes assessment format decisions. Program-level data comparing outcomes across assessment methods supports ethical, evidence-based policy.

Assessment & Decision-Making

Choosing between formal preference assessment and in-the-moment reinforcer analysis requires a structured decision process. BCBAs should consider several client and context variables before defaulting to either approach.

First, assess client history with each format. Does the client have a well-established reinforcer hierarchy that has been validated across multiple sessions and assessors? If so, IMA may be a reasonable real-time supplement. If the client is new, shows rapid preference shifts, or has a history of satiation effects mid-session, more frequent formal assessments are warranted.

Second, consider the behavior target and instructional context. For highly structured discrete trial training where response rate is the primary dependent variable, knowing exactly which reinforcer is most potent at session start may justify a brief formal assessment. For naturalistic teaching environments where reinforcer delivery is embedded and frequent, IMA aligns more naturally with the instructional flow.

Third, evaluate the client's behavioral presentation during assessment itself. If conducting a formal preference assessment is aversive or reliably occasions problem behavior, the time and behavior cost may outweigh the informational value — particularly if IMA can be implemented cleanly. BCBAs should document this rationale and monitor whether IMA produces adequate responding.

Fourth, review data on response rates under each condition. If the organization has collected comparative data across assessment formats, that information should drive the decision. If no such data exists, the decision should be treated as a clinical experiment: define the independent variable (assessment format), specify the dependent variable (response rate), collect data, and evaluate.

Finally, build in a review cycle. Whether using formal assessments or IMA, preference information has a limited shelf life. BCBAs should establish a schedule for reassessment — formal or embedded — and communicate that schedule clearly to all team members implementing the program. This prevents drift toward relying on outdated preference data.

What This Means for Your Practice

This course offers a practically relevant lens on a procedural question that affects every ABA session: how to identify what a client wants right now, in a way that is both accurate and feasible.

The comparison between paired stimulus and in-the-moment reinforcer analysis is not a competition between a rigorous method and a shortcut. Both have procedural integrity requirements; both can be implemented well or poorly. What the research described in this course offers is empirical comparison — the kind of data BCBAs need to make defensible programmatic decisions rather than defaulting to habit.

For practitioners, the immediate takeaway is to treat preference assessment as a clinical decision, not an administrative routine. Ask: what method is most appropriate for this client at this stage of treatment, in this instructional context, given what I know about their reinforcer history? Document that reasoning.

For supervisors, this course points toward the value of building program-level comparison data. If your organization runs 50+ clients and has never systematically compared outcomes across assessment formats, you are making population-level decisions without population-level evidence. Even a small-scale within-subjects comparison in your own program can yield clinically useful information.

For RBT trainers, the content reinforces the importance of training staff on observable reinforcer indicators during tasks — consumption, engagement duration, proximity seeking, and verbal behavior — so that IMA is implemented as a systematic observation procedure rather than casual guesswork.