Preference Assessments in ABA

Summary: This page explains preference assessments, which are systematic procedures used to identify potential reinforcers. You’ll learn about the four main types of preference assessments (MSWO, paired-stimulus, free operant, and single-stimulus), when to use each type, how to implement them correctly, and how to interpret the results to create reinforcer hierarchies for effective behavior change programs.

Preference assessments are systematic procedures used to identify items, activities, or stimuli that may function as reinforcers for an individual. These assessments are crucial because effective reinforcers increase the likelihood of behavior change and skill acquisition.

Why Preference Assessments Matter

Preference assessments serve several important purposes:

• Identify potential reinforcers: Discover what motivates the client
• Create reinforcer hierarchies: Determine which items are most preferred
• Prevent satiation: Identify a variety of reinforcers to use in rotation
• Individualize interventions: Tailor programs to the client’s specific preferences
• Increase intervention effectiveness: Use preferred items to maximize motivation
• Save time and resources: Focus on items that are likely to be effective

Types of Preference Assessments

1. Multiple-Stimulus Without Replacement (MSWO)

The MSWO assessment presents multiple items simultaneously and removes each selected item from subsequent trials.

Procedure

1. Gather materials: Select 5-8 items to assess
2. Arrange items: Place items in a line or array in front of the client
3. Provide instruction: Say “Pick one” or similar instruction
4. Allow selection: Client selects one item
5. Provide access: Allow brief access to the selected item (15-30 seconds)
6. Remove item: Take away the selected item
7. Rearrange remaining items: Reposition items to control for position bias
8. Repeat: Continue until all items are selected or no selection is made
9. Conduct multiple sessions: Repeat the entire process 2-3 times for reliability

Scoring

• Rank items: Assign ranks based on selection order (first selected = highest rank)
• Calculate percentage: Divide rank by number of items and multiply by 100
• Create hierarchy: Arrange items from most to least preferred

Example

With 5 items, if a client selects items in this order: toy car, bubbles, puzzle, book, ball:

• Toy car: Rank 1 (100%)
• Bubbles: Rank 2 (80%)
• Puzzle: Rank 3 (60%)
• Book: Rank 4 (40%)
• Ball: Rank 5 (20%)

Advantages

• Relatively quick: Typically takes 5-10 minutes
• Clear hierarchy: Provides distinct preference rankings
• Efficient: More time-effective than paired-stimulus assessments
• Good reliability: Results are typically consistent across sessions

Limitations

• Requires scanning skills: Client must be able to scan multiple items
• Discrimination demands: Client must distinguish between several options
• Position bias: May be affected by item placement despite rearrangement

2. Paired-Stimulus (PS) Assessment

The paired-stimulus assessment presents two items at a time and records which item is selected from each pair.

Procedure

1. Gather materials: Select items to assess
2. Present pairs: Show two items at a time, equidistant from the client
3. Provide instruction: Say “Pick one” or similar instruction
4. Allow selection: Client selects one item
5. Provide access: Allow brief access to the selected item
6. Record selection: Note which item was chosen
7. Present new pair: Continue with a new combination of items
8. Complete all pairs: Each item should be paired with every other item exactly once

Scoring

• Calculate selection percentage: For each item, divide the number of times it was selected by the number of times it was presented
• Create hierarchy: Arrange items from highest to lowest percentage

Example

With 4 items (A, B, C, D), there are 6 possible pairs. If item A is selected over B, C, and D; item B is selected over C and D; and item C is selected over D:

• Item A: Selected 3/3 times presented (100%)
• Item B: Selected 2/3 times presented (67%)
• Item C: Selected 1/3 times presented (33%)
• Item D: Selected 0/3 times presented (0%)

Advantages

• More precise discrimination: Simpler choice between just two items
• Good for clients with limited scanning: Only requires attending to two items
• High reliability and validity: Well-established in research
• Controls for position bias: Items can be easily repositioned

Limitations

• Time-consuming: Requires many trials with multiple items
• Satiation effects: Client may lose interest during lengthy assessment
• Multiple presentations: Each item is presented multiple times

3. Free Operant Assessment

The free operant assessment allows the client to interact freely with multiple items simultaneously.

Procedure

1. Gather materials: Select items to assess
2. Arrange environment: Place all items within reach of the client
3. Allow free access: Client can interact with any items
4. Observe interaction: Record which items the client engages with and for how long
5. Time the session: Typically conducted for 5-10 minutes

Scoring

• Calculate engagement percentage: For each item, divide the time engaged with the item by the total session time
• Create hierarchy: Arrange items from highest to lowest engagement percentage

Example

During a 10-minute session, if a client engages with:

• Toy car: 4 minutes (40%)
• Bubbles: 3 minutes (30%)
• Puzzle: 2 minutes (20%)
• Book: 1 minute (10%)
• Ball: 0 minutes (0%)

Advantages

• Most naturalistic: Resembles typical play/leisure situations
• Minimal adult prompting: Reduces social influence on selections
• Reduces selection of non-preferred items: Client only engages with truly preferred items
• Good for clients with impulsivity: Allows switching between items

Limitations

• Less structured: May not identify clear hierarchy for similar preferences
• Difficult with activities: Works better with tangible items than activities
• Perseveration risk: Some clients may perseverate on a single item
• Space requirements: Needs enough space for all items to be accessible

4. Single-Stimulus Assessment

The single-stimulus assessment presents one item at a time and measures approach or engagement.

Procedure

1. Gather materials: Select items to assess
2. Present one item: Place a single item in front of the client
3. Record approach: Note whether the client approaches/engages with the item
4. Measure duration: Record how long the client engages with the item
5. Remove item: Take away the item after a set time or when engagement ends
6. Present next item: Continue with each item
7. Repeat presentations: Present each item multiple times in random order

Scoring

• Calculate approach percentage: For each item, divide the number of approaches by the number of presentations
• Calculate average duration: For each item, calculate the average engagement time
• Create hierarchy: Arrange items based on approach percentage and duration

Advantages

• Simplest discrimination task: Only requires attending to one item
• Good for clients with severe disabilities: Minimal cognitive demands
• Identifies absolute preference: Shows if items are preferred at all, not just relatively
• Useful for initial assessment: Can identify if items have any value

Limitations

• Time-consuming: Requires multiple presentations of each item
• No preference hierarchy: Doesn’t show relative preference between items
• May overestimate preference: Items might be selected due to lack of alternatives

Considerations for Preference Assessments

When to Conduct Preference Assessments

• Before beginning intervention: Identify initial reinforcers
• Periodically during intervention: Account for changing preferences
• After preference shifts: When previously effective reinforcers lose value
• When introducing new potential reinforcers: Test new items
• When intervention effectiveness decreases: Reassess motivation

Types of Stimuli to Assess

• Edible items: Food and drinks
• Tangible items: Toys, objects, electronics
• Social interactions: High-fives, praise, attention
• Activities: Games, outings, privileges
• Sensory experiences: Lights, sounds, textures

Factors Affecting Preference

• Satiation: Recent access may decrease preference
• Deprivation: Lack of access may increase preference
• Setting: Preferences may vary across environments
• Time of day: Preferences may change throughout the day
• Health factors: Illness or medication may affect preferences
• Developmental changes: Preferences evolve as clients develop

Validating Preferences as Reinforcers

Preference does not guarantee reinforcement effectiveness. To validate:

1. Conduct reinforcer assessment: Test if preferred items increase target behavior
2. Use preferred items in teaching: Observe if learning improves
3. Compare high vs. low preference items: Measure differential effects
4. Monitor response to reinforcement: Track ongoing effectiveness

RBT Responsibilities in Preference Assessment

As an RBT, you may be responsible for:

• Gathering materials: Collecting items for assessment
• Implementing procedures: Following assessment protocols
• Recording data: Documenting selections and engagement
• Calculating results: Determining preference hierarchies
• Reporting findings: Communicating results to the BCBA
• Using identified reinforcers: Incorporating preferred items in programs

Practice Example

An RBT conducts an MSWO preference assessment with 6 items. The client selects the items in this order across three sessions:

Session 1: Tablet, stickers, car, blocks, crayons, ball Session 2: Tablet, car, stickers, crayons, ball, blocks Session 3: Tablet, stickers, car, ball, crayons, blocks

Question: What is the overall preference hierarchy based on average rank?

Solution:

1. Assign ranks for each session (1 = highest preference, 6 = lowest)
2. Calculate average rank for each item across sessions
3. Create hierarchy from lowest average rank (most preferred) to highest (least preferred)

Item	Session 1 Rank	Session 2 Rank	Session 3 Rank	Average Rank
Tablet	1	1	1	1.0
Stickers	2	3	2	2.3
Car	3	2	3	2.7
Blocks	4	6	6	5.3
Crayons	5	4	5	4.7
Ball	6	5	4	5.0

Final hierarchy:

1. Tablet (most preferred)
2. Stickers
3. Car
4. Crayons
5. Ball
6. Blocks (least preferred)

Key Points to Remember

• Preference assessments systematically identify potential reinforcers
• Different assessment methods have unique advantages and limitations
• Preferences change over time and should be reassessed regularly
• Preference does not guarantee reinforcement effectiveness
• Multiple types of reinforcers should be identified to prevent satiation
• Assessment method should match client abilities and assessment goals