Why Preference Assessments Matter in ABA
Effective reinforcement is the cornerstone of every ABA intervention, and you cannot reinforce effectively without knowing what the learner actually prefers. Preference assessments are systematic methods for identifying potential reinforcers by observing how a learner interacts with various stimuli. Unlike simply asking a caregiver what a child likes, formal preference assessments provide objective, data-driven information about stimulus preference hierarchies.
The BCBA exam tests your knowledge of multiple preference assessment methods, including when to use each one, how to conduct them, and how to interpret the results. This guide covers the four major types you need to know.
Free Operant Preference Assessment
The free operant observation is the simplest and least intrusive preference assessment. During a free operant assessment, you provide the learner with unrestricted access to a variety of stimuli and observe which items they approach, engage with, and spend the most time using. There are no trials, no restrictions, and no programmed consequences.
How to Conduct a Free Operant Assessment
Arrange several items in the environment and allow the learner to move freely among them for a set period, typically 5 to 10 minutes. Record the duration of engagement with each item. The items with the highest percentage of engagement time are considered the most preferred.
Advantages and Limitations
- Quick to administer and requires minimal materials
- Low demand on the learner, making it suitable for individuals who do not tolerate structured assessments
- Does not produce a clear rank ordering of preferences
- Results may be influenced by the physical arrangement of items in the room
Single Stimulus (Successive) Preference Assessment
In the single stimulus method, items are presented one at a time, and the practitioner records whether the learner approaches or engages with each item. This method is sometimes called the successive choice method because each trial involves only one stimulus.
This approach is useful for learners who have difficulty choosing between two items presented simultaneously. However, it tends to identify many items as "preferred" because learners may approach most items when no alternative is available. It does not produce a fine-grained preference hierarchy.
Paired Stimulus (Forced Choice) Preference Assessment
The paired stimulus preference assessment, originally described by Fisher and colleagues in 1992, is often considered the gold standard for identifying preference hierarchies. Every item is paired with every other item across multiple trials, and the learner chooses one item from each pair.
How to Conduct a Paired Stimulus Assessment
Select 5 to 7 items to assess. Present two items simultaneously, positioned equidistant from the learner. Allow the learner to select one item and briefly interact with it (typically 20 to 30 seconds). Record which item was selected. Rotate through all possible pairs, counterbalancing left and right positions. Calculate the percentage of trials in which each item was selected.
Advantages and Limitations
- Produces a clear rank ordering of preferences from most to least preferred
- Highly reliable and well-supported by research
- Time-consuming, especially with many items (the number of trials equals n(n-1)/2 where n is the number of items)
- Requires the learner to make a selection on each trial, which may be difficult for some individuals
Multiple Stimulus Without Replacement (MSWO)
The MSWO, developed by DeLeon and Iwata in 1996, presents all items simultaneously in an array. The learner selects one item, engages with it briefly, and then the array is re-presented without that item. This continues until all items have been selected or the learner stops choosing.
How to Conduct an MSWO Assessment
Arrange 5 to 7 items in a line in front of the learner. Randomize the positions of items in the initial array. When the learner selects an item, allow brief access (about 30 seconds), then remove that item from the array. Re-present the remaining items with positions re-randomized. Continue until all items are selected or the learner makes no selection within 30 seconds. Repeat the entire sequence for 3 to 5 sessions and calculate each item's average rank.
Advantages and Limitations
- Produces a rank-ordered hierarchy similar to the paired stimulus method
- Significantly faster to administer than the paired stimulus method
- Good balance between efficiency and accuracy
- May be affected by position bias if items are not properly randomized
- Removing items changes the available options, which could influence later selections
Choosing the Right Assessment for the Situation
For the BCBA exam, knowing which method to recommend in a given scenario is critical. Use the free operant method as a quick screening tool or when the learner cannot tolerate structured assessments. Use the paired stimulus method when you need the most precise hierarchy and have sufficient time. Use the MSWO when you need a reliable hierarchy but want to save time. Use the single stimulus method for learners who struggle with simultaneous choices. Remember that preference can change rapidly, so reassessing frequently is always best practice.