What is MSW?
Multiple Stimulus WITH Replacement (MSW) involves presenting an array of items (usually 3 or more). When the client chooses an item, they consume/play with it, and then the item is placed back into the array (Replaced) for the next trial.
Example:
Trial 1: [Apple, Cookie, Chip]. Client picks Cookie.
Trial 2: [Apple, Cookie, Chip] (Cookie is back!). Client picks Cookie.
For your RBT practice test, this is the key difference from MSWO. In MSW, the client can pick the same favorite item every single time. It tells us what they like, but not necessarily a hierarchy of the other items.
When is MSW Used?
It is rarely used for tangible items (toys) because we want a hierarchy. However, it is useful for Edibles or when checking if a preference is stable. If they pick the cookie 10/10 times, we know the cookie is a very potent reinforcer right now.
It creates a less sensitive hierarchy than MSWO. If they only pick Cookie, we have no idea if they like Chips or Apples better as a second choice.
Clinical Procedure
1. Present array (A, B, C).
2. Client picks B.
3. Allow access.
4. Put B back in the array (Replace it).
5. Shuffle positions.
6. Present array (C, B, A). Client can pick B again.
RBT Practice Exam Scenario
Question: "An RBT conducts an assessment where the chosen item is returned to the array for the next trial. What is this called?"
Answer: Multiple Stimulus WITH Replacement (MSW).
Frequently Asked Questions About MSW
Why would I use MSW instead of MSWO?
If you want to assess how frequently a single item is chosen when other options are available. It assesses the strength of a single reinforcer.
Does MSW create a hierarchy?
Poorly. If the client picks the favorite item every time, you get no data on the other items.
What is the "Replacement" part?
The chosen item is returned to the field of choice, making it available again for the next trial.
Does it take longer than MSWO?
Yes, potentially, because the number of items never decreases.
Can I use this for identifying dietary preferences?
Yes. If a child eats the pretzel every time it is offered, even when chocolate is present, that is strong data.