Almost every skill-acquisition and behavior-reduction plan you write depends on having effective reinforcers. Preference assessments are how you find good candidates quickly and systematically, instead of guessing.
Why it matters
A plan built on a weak reinforcer can look like a failed teaching procedure when the real problem is the consequence. Preference assessments reduce that risk by sampling the client's own choices. As a BCBA, you will pick the format, train staff to run it, and decide what the results mean. The practice items for this task cover all three: matching a format to a client, calculating results, and knowing the limits of what a preference assessment can tell you.
Key ideas
- Preference is a prediction, not proof. An item that is chosen often is likely to function as a reinforcer. Only a reinforcer assessment, where the item is delivered contingent on a response and that response increases, confirms reinforcing value.
- Indirect methods come first, not last. Interviews, surveys, and checklists completed by the client or caregivers generate a list of candidate items. They are fast but less accurate than direct observation, so use them to choose what to test.
- Direct methods vary in structure.
- Free-operant: the client has open access to an array of items for a set time, and you record how long they engage with each. Nothing is withdrawn.
- Single-stimulus (successive choice): one item at a time; you record approach or engagement.
- Paired-stimulus (forced choice): two items per trial, and every item is paired with every other item.
- Multiple-stimulus with replacement (MSW): the chosen item is returned, so every item stays available on every trial.
- Multiple-stimulus without replacement (MSWO): the chosen item stays out, so the array shrinks with each trial until all items are ranked.
- Each format has a trade-off. Paired-stimulus gives a clear hierarchy but takes the most trials. MSWO gives a hierarchy in less time. Single-stimulus suits clients who cannot yet choose among several items, but it can overestimate preference and gives a weak ranking. Free-operant formats tend to evoke less problem behavior because items are never taken away, but if the client engages with one item the whole time, you learn little about the others.
- Preferences change. Satiation, deprivation, and new experiences shift what a client wants. Brief assessments repeated often, such as a quick MSWO before a session, keep your reinforcers current.
- Edibles can mask leisure items. When food and toys share an array, edibles are often chosen first. If you need leisure reinforcers, assess them separately.
Definitions
- Preference assessment: a structured way to identify stimuli a person prefers, which are therefore likely to work as reinforcers.
- Reinforcer assessment: a test of whether a stimulus increases a response when delivered contingent on that response.
- Selection percentage: the number of times an item was chosen divided by the number of times it was available, multiplied by 100.
- Position bias: choosing based on where an item sits (for example, always the left side) rather than what it is.
Examples from a session
Matching the format to the client
- Paired-stimulus: Amara, age 6, can scan two items. Her BCBA tests 6 toys. Each toy appears in 5 trials (one with each other toy), for 15 trials total. Her ball is chosen in 5 of 5 trials (100 percent) and her puzzle in 1 of 5 (20 percent).
- MSWO: Before each clinic session, an RBT puts 5 snacks in a row in front of Mr. Ortiz, an adult client. He picks one, eats it, and the RBT rearranges the remaining items. The order of selection becomes the rank, and the rank is averaged over three rounds.
- Free-operant: Kai, age 10, hits when toys are removed. His BCBA lays out 6 items in a home play area for 5 minutes and records seconds of engagement with each. Nothing is taken away, so the assessment avoids the trigger.
- Single-stimulus: Lena, a teenager who does not yet choose between items, is offered one item at a time across trials while staff record whether she approaches or engages within a few seconds.
Non-example: asking Kai's parents which toys he likes is an indirect method. It suggests candidates but is not a direct preference assessment.
Whatever the format, give the client a chance to sample each item first, define the selection response (reach, touch, point, or eye gaze), and rotate item positions across trials.
Common mistakes / exam traps
- Treating the top item as a confirmed reinforcer. If responding does not increase when the item is delivered contingently, it is not functioning as a reinforcer for that task, no matter how highly it ranked.
- Dividing by the wrong number. In a paired-stimulus assessment, divide by the trials in which the item was presented, not by the total number of trials or the number of items.
- Ignoring motivation. Running an edible assessment right after lunch can make foods look less preferred than they are at other times of day.
- Overlooking the client's voice. Ask the client and their family, and include culturally relevant items the family values, rather than relying on a standard clinic kit.
Exam trap
When a stem says problem behavior occurs when preferred items are removed, look for the free-operant format. When it says the client cannot scan or choose between items, look for single-stimulus.
Exam trap
MSW vs MSWO turns on what happens to the chosen item. In MSWO it stays out, so the array shrinks and every item ends up ranked. In MSW it goes back, so one strong item can win every trial and leave the rest unranked.
Quick check
During a paired-stimulus assessment with item positions varied across trials, Theo picks whichever item is on his right in almost every trial. What is the most defensible interpretation?