What is Paired Stimulus?
Paired Stimulus (also called "Forced Choice") is the Gold Standard of preference assessments. You present two items simultaneously and ask the client to "Pick one."
Every item is paired with every other item.
- Trial 1: Apple vs. Ball (Picks Apple)
- Trial 2: Apple vs. Car (Picks Apple)
- Trial 3: Ball vs. Car (Picks Car)
This creates a clear hierarchy: Apple (Won 2), Car (Won 1), Ball (Won 0). We know exactly what the client wants most.
For your RBT practice test, knowing that Paired Stimulus produces the most accurate hierarchy is a common exam question.
Why is it the Best?
It forces a trade-off. The client has to decide. This helps differentiate between high-preference (highly motivating) and medium-preference items. In Single Stimulus, they might take both. In Paired, they show you their true favorite.
Procedure
1. Place two items in front of the client.
2. Say "Pick one."
3. Block attempts to grab both.
4. Client engages with the choice for 15-30 seconds.
5. Remove both and present the next pair.
Drawbacks
It is time-consuming. If you have 10 items, that is 45 trials! It can also be frustrating for the client because you are constantly taking items away.
Frequently Asked Questions About Paired Stimulus
What is the main advantage of Paired Stimulus?
It produces the most distinct, accurate hierarchy of preferences.
What is the main disadvantage?
It takes a long time to administer compared to MSWO or Free Operant.
What happens if the client grabs both items?
You block the attempt and re-present the trial. If they persist, you might need to switch to Single Stimulus.
How many items should I test?
Usually 5 to 7 items. Testing more than that creates an exponential number of trials that takes too long.
What is "position bias"?
When a client just picks whatever is on the Right (or Left) side. We control for this by switching the position of items in every trial.
Can I use pictures instead of real objects?
Yes, if the client has the skill to match pictures to objects. This is common for activity reinforcers (e.g., "Park" vs. "YouTube").