What is MSWO?
Multiple Stimulus Without Replacement (MSWO) involves presenting an array of items (usually 5 to 7) to the client. The client picks one. They get to play with it. Then, for the next trial, that item is removed (not replaced). The client picks from the remaining items.
Trial 1: [A, B, C, D, E] -> Client picks A.
Trial 2: [B, C, D, E] -> Client picks C.
Trial 3: [B, D, E] -> Client picks B.
This creates a hierarchy quickly. "A" was their 1st choice, "C" was their 2nd, etc.
For your RBT practice test, remember that MSWO is the choice when you want a hierarchy but need it faster than Paired Stimulus.
Why "Without Replacement"?
By removing the favorite item, we force the client to pick their next favorite. If we put "Item A" back (Replacement), they might just pick "A" every single time, and we would never learn what their second favorite item is.
Procedure
1. Array of 7 items. "Pick one."
2. Client picks. Plays for 30s.
3. Remove item. Shuffle remaining items.
4. "Pick one."
5. Repeat until no items are left.
RBT Practice Exam Scenario
Question: "An RBT presents 5 items. The child picks the red car. The RBT removes the red car and presents the remaining 4 items. What assessment is this?"
Answer: MSWO.
Frequently Asked Questions About MSWO
What does MSWO stand for?
Multiple Stimulus Without Replacement.
Why is it faster than Paired Stimulus?
Because you rank 7 items in just 7 trials. Paired stimulus would take 21 trials for the same number of items.
Who is this appropriate for?
Clients who can scan an array of multiple items. It is not good for clients with poor visual attention.
What if the client wants the removed item?
They might look for it. You must ensure it is out of sight so they focus on the remaining options.
What is the difference between MSW and MSWO?
In MSW (With Replacement), the chosen item is put back. In MSWO (Without Replacement), it is gone. MSWO is better for hierarchies.
Do I shuffle the items?
Yes. After every trial, rearrange the remaining items to prevent position bias.