ABA glossary
Multiple-stimulus without replacement
Also called MSWO
Definition
A preference assessment in which several items are presented at once, the chosen item is not returned, and the remaining items are rearranged and offered again until all are chosen or the learner stops choosing.
In plain words
In an MSWO, the learner picks from an array (often 5 to 8 items), gets brief access to the chosen item, and that item stays out for the rest of the series. Because the favorite is removed, the learner has to choose among the remaining items, which produces a full ranking in less time than a paired-stimulus assessment. The order of selection is the ranking: first picked is most preferred. Several series are often run and the ranks combined.
Example from a session
The RBT lines up five items in front of Malik and says "Pick one." He chooses the puzzle and plays with it for 20 seconds. The RBT puts the puzzle away, moves the remaining four items into a new order, and offers the array again. Malik chooses the car, then the music toy, then crackers, then the ball. The RBT records the order 1 to 5 on the data sheet.
For BCBA candidates and supervisors
MSWO requires the learner to scan an array and make a single selection, so analysts teach or check those prerequisites first. Rotating item positions after each selection reduces position bias. Because items are removed, MSWO can evoke problem behavior in some learners; analysts then consider a free-operant format. Brief MSWOs (one series) are practical for frequent, in-session preference checks, which help track daily shifts in preference.
Often confused with multiple-stimulus with replacement, paired-stimulus preference assessment
Without replacement means the chosen item is removed from later trials, so every item eventually gets ranked. With replacement (MSW) means the chosen item is returned each time and unchosen items are swapped for new ones, so the favorite keeps getting picked and lower items get little information. Paired-stimulus presents two items at a time instead of an array.
Exam tip
Remember the name literally: "without replacement" means the chosen item does not go back. If a stem says the chosen item is returned and the others are replaced, the answer is MSW, not MSWO.
Can you spot multiple-stimulus without replacement in a scenario?
Practice RBT B.1 with exam-style questions and instant feedback.