By Matt Harrington, BCBA · Behaviorist Book Club · Research-backed answers for behavior analysts
A paired stimulus (PS) preference assessment presents two stimuli simultaneously to the client, who selects one by approaching, touching, or taking it. Over multiple trials, each item is paired with every other item, generating a relative preference hierarchy based on selection frequency. It is one of the most widely validated formats for identifying potential reinforcers, though it requires more trials than single-stimulus or free-operant approaches and can be time-consuming when many items are included.
In-the-moment reinforcer analysis (IMA) embeds the identification of potential reinforcers within the instructional activity rather than conducting a separate assessment phase beforehand. The clinician presents options during the task and observes the client's approach, engagement, and consumption behavior to determine which item is currently functioning as a reinforcer. This makes it more time-efficient and ecologically valid compared to traditional preference assessment formats.
The appropriate frequency depends on the individual client and the stability of their reinforcer hierarchy. For many clients in intensive ABA programs, assessments are conducted at the beginning of each session or multiple times per day because reinforcer value shifts due to satiation and motivating operations. BCBAs should establish a reassessment schedule based on data — specifically, by monitoring response rates and reinforcer effectiveness over time and adjusting assessment frequency accordingly.
Not necessarily, and the answer depends on the client and context. IMA may be sufficient for clients with stable, well-documented preference histories in naturalistic teaching environments. For clients who are new, show rapid preference shifts, or require highly structured instruction where reinforcer potency must be maximized, periodic formal assessments remain valuable. Many practitioners use IMA as a real-time supplement rather than a full replacement for scheduled formal assessments.
If response rates decline, latency increases, or the client engages in escape behavior during the task, the item selected through IMA may not be functioning as a reinforcer in that moment. BCBAs and RBTs should monitor these behavioral indicators in real time. When they appear, it signals a need to reassess — either by offering a different item in the moment, taking a brief break, or conducting a more structured preference check before resuming instruction.
Satiation reduces the reinforcing value of any stimulus over repeated exposure. Formal preference assessments conducted at session start may not reflect reinforcer value mid-session if high-preference items have been used heavily. IMA is particularly responsive to satiation because it evaluates preference at the moment of delivery rather than predicting it from an earlier hierarchy. This is one reason IMA may be advantageous in longer sessions where reinforcer effectiveness may drift across time.
Code 2.01 requires behavior analysts to provide effective treatment grounded in scientific evidence. Code 2.09 requires ongoing evaluation of treatment efficacy. Together, these codes establish that reinforcer identification is not a one-time event but an ongoing empirical responsibility. Code 2.13 requires that assessment results directly inform behavior change programs, meaning preference assessment findings must be systematically documented and applied, whether the method used is formal or in-the-moment.
RBTs should be trained to identify observable indicators of reinforcer value during tasks, including approach behavior, consumption speed, engagement duration, and request behavior. Training should include explicit criteria for what counts as selection in an IMA context, how to document which item was used, and what behavioral signals indicate the reinforcer may no longer be effective. Role-play and in-session feedback from supervisors are more effective training formats than reading alone for building this skill.
IMA requires that the client demonstrate observable preference indicators — approach, engagement, or consumption — for the clinician to interpret. For clients with very limited motor responses, severe attending deficits, or profiles where passive tolerance is difficult to distinguish from active preference, IMA may be harder to implement reliably. In these cases, structured forced-choice or free operant formats with clear operational definitions of selection behavior may produce more interpretable data.
BCBAs comparing formal and IMA formats should track: response rate during instruction, latency to response, percentage of trials with problem behavior or refusal, and overall session completion rate. Comparing these variables across sessions using one format versus the other — ideally in an alternating treatment or reversal design — provides within-client data to guide programmatic decisions. Documenting which format was used and under what conditions strengthens the validity of any conclusions drawn.
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All behavior-analytic intervention is individualized. The information on this page is for educational purposes and does not constitute clinical advice. Treatment decisions should be informed by the best available published research, individualized assessment, and obtained with the informed consent of the client or their legal guardian. Behavior analysts are responsible for practicing within the boundaries of their competence and adhering to the BACB Ethics Code for Behavior Analysts.