2.3 Preference and Reinforcer Assessments (MSWO, Paired-Choice, Free Operant)

Preference and Reinforcer Assessments

Critical Distinction: A Preference Assessment identifies stimuli that a person chooses or interacts with most frequently. A Reinforcer Assessment goes a step further to empirically verify whether contingent presentation of a preferred stimulus actually functions as a reinforcer by increasing or maintaining the rate of a target behavior. Preference does not equal reinforcement potency under high effort demands.

Indirect vs. Direct Preference Assessments

• Indirect Preference Assessments: Gather reports via interviews, checklists, or surveys (e.g., Reinforcer Assessment for Individuals with Severe Disabilities - RAISD). While fast, indirect reports frequently reflect caregiver preferences rather than client preferences.
• Direct Preference Assessments: Systematically measure client approach, selection, or engagement behaviors when presented with physical stimuli, activities, or sensory items.

Direct Preference Assessment Methodologies

1. Single-Item / Successive Choice (Pace et al., 1985)

• Procedure: Stimuli are presented one at a time in randomized order. The analyst measures whether the learner approaches/touches the item and tracks total engagement duration.
• Best Used For: Individuals who struggle to select between two or more array choices or who display severe side-bias.
• Limitation: Tends to yield high false positives—learners often approach nearly all items presented individually, making it difficult to establish a refined preference hierarchy.

2. Paired-Choice / Forced-Choice (Fisher et al., 1992)

• Procedure: Two items are presented simultaneously. The analyst instructs the learner to make a choice. Once an item is selected, the non-chosen item is immediately removed. Every item in the pool is paired with every other item across randomized trials.
• Formula for Total Trials: For $N$ items, total trials $= \frac{N(N-1)}{2}$. (e.g., 6 items yield 15 trials).
• Best Used For: Creating a highly accurate, distinct rank-ordered preference hierarchy.
• Limitation: Time-consuming; can evoke problem behavior if selected items are removed too quickly.

3. Multiple Stimulus Without Replacement (MSWO; DeLeon & Iwata, 1996)

• Procedure: An array of 5 to 7 items is placed in front of the learner. When the learner selects an item, they are allowed brief access (e.g., 15–30 seconds). The selected item is removed from the array, the remaining items are rotated/reshuffled, and the learner chooses again from the smaller array.
• Best Used For: Efficiently establishing a preference hierarchy in a short timeframe (10–15 minutes).
• Advantage: Prevents a single highly preferred item from monopolizing every selection trial.

4. Multiple Stimulus With Replacement (MSW)

• Procedure: Similar to MSWO, but after an item is selected and accessed, it is returned to the array for the next trial.
• Limitation: Learners frequently select the same top-preferred item on every trial, masking preferences for remaining items in the array.

5. Free Operant Preference Assessments

In Free Operant assessments, the learner has continuous, unrestricted access to an array of items. No items are removed by the clinician, and no demands are placed.

• Naturalistic Free Operant: Observed in the client's natural environment (e.g., playroom or home).
• Contrived Free Operant: Clinician sets up a specific room with predetermined items, places the client in the room, and records cumulative duration of engagement with each item.
• Key Advantage: Eliminates problem behaviors evoked by item removal or forced transitions; ideal for clients with severe tangible-evoked aggression.

Preference Assessment Method Comparison Matrix

Reinforcer Assessment Procedures

Once a preference assessment identifies potential reinforcers, a reinforcer assessment is conducted to determine whether contingent presentation of those stimuli increases or maintains target response rates under specific schedule conditions.

Progressive-Ratio (PR) Schedule Breaking Point Visualization
Reinforcer A (High Potency):  PR2 -> PR4 -> PR8 -> PR16 -> PR32 -> PR64 (Break Point = 64 responses)
Reinforcer B (Low Potency):   PR2 -> PR4 -> PR8 (Break Point = 8 responses)

1. Concurrent Schedule Reinforcer Assessment

Two or more schedules of reinforcement operate simultaneously for two distinct behaviors. For example, pressing Button A earns Access to Toy X on an FR1 schedule, while pressing Button B earns Access to Toy Y on an FR1 schedule. This directly measures relative reinforcer efficacy (which item the learner works harder or more frequently to obtain).

2. Multiple Schedule Reinforcer Assessment

A single behavior is reinforced by different stimuli across alternating components of a schedule, each signaled by a distinct discriminative stimulus ($S^D$).

3. Progressive-Ratio (PR) Schedule Reinforcer Assessment

In a Progressive-Ratio (PR) schedule, the response requirement systematically increases after each earned reinforcer (e.g., FR1, FR2, FR4, FR8, FR16, FR32...).

• Breaking Point: The session continues until the learner ceases responding for a predetermined duration. The ratio requirement at which responding stops is the breaking point.
• Clinical Utility: PR assessments measure reinforcer strength/potency under increasing effort demands, helping behavior analysts select reinforcers that will maintain behavior during difficult learning tasks.