What Is a Free Operant Preference Assessment in ABA Therapy?
A free operant preference assessment (FOPA) is an Applied Behavior Analysis (ABA) method for identifying which items, activities, or stimuli a learner finds most preferred. During a FOPA, the behavior technician gives the learner free, simultaneous access to an array of items in the environment. The learner moves between items as they wish, and the technician records the duration of time the learner spends engaged with each one. The items with the longest engagement duration are assumed to be the most preferred and are likely to function as reinforcers when used in teaching programs.
The FOPA is one of several preference assessment formats used in ABA. Others include the paired stimulus (PS) assessment, where two items are presented at a time and the learner chooses one, and the multiple stimulus without replacement (MSWO), where an array of items is presented and the chosen item is removed before the next trial. Each format produces a ranking of preferred items, but they differ in how the array is structured and how preference is measured.
According to a 2012 study in the Journal of Applied Behavior Analysis available through PubMed Central at the National Institutes of Health, the free operant assessment involves unrestricted access to multiple items simultaneously and can typically be completed in 5 to 10 minutes. The dependent measure is the time the learner allocates to each item. The FOPA is appealing because it’s relatively quick, doesn’t require the team to withhold or remove items mid-assessment, and tends to produce lower rates of interfering behavior than formats that require item removal.
The behavior analyst chooses the FOPA format when its specific features fit the learner and situation—particularly when the learner engages in interfering behavior in response to having items removed, when time is limited, or when the team wants a quick check of current preferences before starting a teaching session. Like all preference assessments, the FOPA produces information about preference, not certainty about reinforcer effectiveness; the team confirms that preferred items actually function as reinforcers by observing their effect on behavior during teaching.
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Examples of Free Operant Preference Assessment in ABA Therapy
Example 1: Identifying reinforcers for a new client
A behavior analyst is starting services with a four-year-old client and needs to identify items that will serve as reinforcers for early teaching programs. The behavior technician arranges eight toys and activities on the floor in a play area: a bubble wand, a slinky, a wind-up toy, a small puzzle, a sensory ball, a pop tube, an art board, and a singing toy. The technician walks the learner around the array to introduce each item, then sits back and records engagement duration as the learner moves freely among them for five minutes. The slinky and pop tube receive the most engagement and become primary reinforcers in early teaching sessions. The team’s use of preferred items as positive reinforcement is foundational to the program.
Example 2: A quick pre-session check
A behavior technician working with a seven-year-old client conducts a brief FOPA at the start of each session to identify which of the learner’s known preferred items are most appealing that day. The technician sets out five items the learner has previously engaged with, observes for three minutes, and uses the data to select the day’s reinforcers. Preferences shift day to day for many learners, so this quick check helps the team avoid using items that have lost their reinforcing value temporarily.
Example 3: Selecting reinforcers for a learner with interfering behavior
A behavior analyst is selecting reinforcers for a nine-year-old client whose functional behavior assessment showed that interfering behavior is sometimes triggered by having items taken away. The analyst chooses the FOPA format specifically because the procedure doesn’t require removing items from the learner. The therapist sets up the array, and the learner moves freely among the items for the full assessment window. The data identifies preferred items the team can use as reinforcers without the procedure itself evoking the interfering behavior the team is working to reduce.
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Why Is Free Operant Preference Assessment Important in ABA?
Preference assessments matter because reinforcement only works if the team is using items the learner actually wants. Assumptions about what a child will find reinforcing are often wrong—preferences vary widely between learners, change over time, and can shift based on context, satiation, and mood. Without systematic preference assessment, the team risks running teaching programs that produce little learning because the supposed reinforcers aren’t actually reinforcing anything. The FOPA gives the team a structured, brief way to identify what’s likely to work on a given day, for a given learner.
The free operant format in particular has specific clinical advantages. It’s quick, often completed in just a few minutes, which makes it practical for daily use. It doesn’t require the behavior technician to remove items from the learner, so the procedure itself is less likely to evoke interfering behavior. It also allows the learner to interact with multiple items naturally, the way they would during free time, which produces information about preference under conditions that resemble real teaching contexts.
The FOPA does have known limitations the team works around. The format produces a higher rate of “false negatives” than formats that present items individually, since a learner might not interact with all available items in the time given. The procedure also tends not to produce as clear a hierarchy of preferences as more structured formats. For these reasons, behavior analysts often combine the FOPA with other assessment methods over time, using the FOPA for quick checks and more structured formats when a complete ranking is needed. For more on how teams individualize ABA programming, see our Q&A about ABA therapy for children with autism.
Preference assessments also fit into the broader cadence of an ABA program. As learners progress, their preferences evolve, and the team needs ongoing information about what motivates engagement at each stage. Regular preference assessments are part of the data-driven decision making that makes ABA programs responsive to the individual learner rather than static across time. For more on how skill-building unfolds over the course of an ABA program, read our blog on how long will my child be in ABA.
Worth noting: preference assessments identify items likely to function as reinforcers, but they don’t prove that an item will reinforce. The team confirms by tracking learning outcomes when the item is used contingent on target behavior. This distinction matters especially for conditioned reinforcers, whose reinforcing value depends on prior pairing with other reinforcers and can shift over time.
FAQs About Free Operant Preference Assessment
How is FOPA different from other preference assessment formats?
FOPA gives the learner free, simultaneous access to an array of items and measures duration of engagement with each. Paired stimulus (PS) assessment presents two items at a time and asks the learner to choose. Multiple stimulus without replacement (MSWO) presents an array but removes each chosen item before the next trial. FOPA is faster and doesn’t require item removal, but it tends to produce less clear preference rankings than PS or MSWO. Behavior analysts choose the format based on the learner and the question they’re trying to answer.
How long does a free operant preference assessment take?
Most FOPAs are 5 to 10 minutes per session. Shorter durations (3 to 5 minutes) can work for quick daily checks, while longer durations may be used when the team wants a more thorough picture. The behavior analyst calibrates the duration to the learner’s attention span and the specific clinical question. Repeated brief sessions over a few days often produce better information than one long session.
Does identifying a preferred item mean it will work as a reinforcer?
Not necessarily. Preference assessments identify items the learner is likely to find reinforcing, but reinforcement is defined by its effect on behavior—whether providing the item after a target behavior actually increases that behavior over time. The team validates preferred items by tracking learning outcomes when those items are used contingent on target responses. An item that wins a preference assessment but doesn’t produce learning when used as a reinforcer isn’t functioning as a reinforcer for that learner, in that context, at that time.
How often should preference assessments be repeated?
Preferences shift, sometimes dramatically. Many teams conduct brief preference assessments at the start of every session, and more comprehensive assessments periodically (weekly or monthly) to track longer-term changes. If the team notices that previously effective reinforcers are losing their impact, that’s a strong signal to run a fresh preference assessment. Building regular preference assessment into the schedule is part of keeping ABA programs responsive to the learner over time.
Can family members conduct a free operant preference assessment at home?
Yes, with coaching. The procedure is straightforward: set out an array of items, give the learner free access, observe and record duration of engagement with each. The behavior analyst or therapist typically demonstrates the procedure and helps the family set up the array, choose items to include, and record data. Information from home preference assessments often differs from clinic-based assessments, which is useful—home preferences inform what the family can use to support skill generalization in the natural environment.
Key Takeaways About Free Operant Preference Assessment
- A free operant preference assessment (FOPA) is an ABA method for identifying preferred items by giving the learner free access to an array and measuring engagement duration with each.
- FOPA is one of several preference assessment formats, alongside paired stimulus (PS) and multiple stimulus without replacement (MSWO).
- The format is quick (typically 5 to 10 minutes), doesn’t require removing items from the learner, and tends to produce lower rates of interfering behavior than formats that require item removal.
- FOPA’s main limitations are a higher rate of false negatives and less clear preference rankings than more structured formats.
- Preference assessments identify items likely to function as reinforcers, but the team confirms reinforcing value by tracking learning outcomes when the items are used contingent on target behavior.
- Regular preference assessments are part of the data-driven decision making that keeps ABA programs responsive to learners whose preferences shift over time.
