What is Free Operant Assessment?

by | Jun 27, 2024

One of the most powerful tools in establishing and maintaining a change in behavior is the use of reinforcement. Reinforcement occurs when a consequence strengthens the behavior that it follows. For example, if lollipops are a reinforcer for a child, then if provided a lollipop after reading, it should increase the reading behavior. When introducing a new skill, it is important that we understand what this individual finds reinforcing. There are many ways we can work to identify reinforcers for someone. One way is to use a Stimulus Preference Assessment; there are many different ways that a Preference Assessment can be completed. Many studies have demonstrated that high-ranked items from Stimulus Preference Assessments are more effective at decreasing challenging behavior and improving performance on academic tasks (Carr, Nicolson, & Higbee, 2000).

So, what is a Stimulus Preference Assessment?

A Stimulus Preference Assessment refers to a variety of procedures used to determine the following:

  • The stimuli that a person prefers
  • The relative preference values of those stimuli
  • The conditions under which those preferences values change
  • …..or in other words, it helps us to know what item (or items) this person will work for

(Cooper, Heron, & Heward, 2007)

There are many types of preference assessments: Multiple Stimulus with Replacement, Multiple Stimulus without Replacement, Forced Choice (paired choice) and Free Operant. The assessment we will focus on is a Free Operant Assessment. With a Free Operant Assessment, the individual has unrestricted access to numerous activities and items for a predetermined amount of time; it’s important to be sure that the items chosen are safe, easily accessible and age appropriate. Any item can be used: activities, toys, games, and even food. All items are easily accessible and are never removed after engagement. There are no response requirements for the individual being observed. They may engage with the item in the way it was intended or use their imagination and other play skills. While the person has free access, the observer of the assessment has a few tasks. The observer should sit back quietly, being sure not to influence the individual’s choices. The observer should also record the activities or items the individual interacts with and the duration of the interaction. It may also be helpful for the observer to indicate in which way the person engaged with the chosen activity.

Types of Preference Assessment

There are a few different ways that a Free Operant Preference Assessment may be presented, such as being in contrived or naturalistic settings. In a contrived Free Operant Assessment, the observer sets up a predetermined number of items within sight and reach of the person; the items are specifically chosen and placed in a designated room with no additional items or distractions present. A contrived observation may be helpful if attempting to determine new reinforcers while making sure other known reinforces are not present in the environment, like an electronic tablet for example. In a naturalistic Free Operant Assessment, the individual can engage freely with items and activities in a familiar, everyday environment; all current and potential reinforcers are available for the individual to engage with. For both types of assessments, the observer watches the individual for a predetermined amount of time without engaging or interacting to avoid influence the individuals’ choices; the observer should be continuously collecting data on the items chosen, frequency of each items chosen, duration of interactions and type of interaction. The items or activities the individual approaches more often and engages with for the longest duration are considered those most highly preferred, while the items that the person does not approach or approaches less often are considered the lowest preferred. Typically, we establish a ranking of preferred to less or non-preferred items by the end of the assessment. It is important to perform assessments regularly as preferences change over time. Assessments also help to introduce new activities or items that may act as reinforcers for an individual.

Free Operant Assessments are fairly easy to implement and are appropriate for people of all ages. A Free Operant Assessment may be best for individuals who engage in challenging behavior when preferred items are taken away since during Free Operant Assessment items are never removed after selection or engagement. This type of stimulus preference assessment may be most appropriate for persons who are unable to select between highly preferred and low-preferred items when provided with these items in an array. One limitation of a Free Operant Assessment is that it may not provide information about a wide variety of potential reinforcers especially if a person always interacts with only one item. If this is the case, a different type of stimulus preference assessment should be conducted.


Carr JE, Nicolson AC, Higbee TS. Evaluation of a brief multiple-stimulus preference assessment in a naturalistic context. J Appl Behav Anal. 2000 Fall;33(3):353-7. doi: 10.1901/jaba.2000.33-353. PMID: 11051581; PMCID: PMC1284262.

Cooper J.O, Heron T.E, Heward W.L. Applied behavior analysis (2nd ed.) Upper Saddle River, NJ: Pearson; 2007.

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