Multiple Stimulus without Replacement (MSWO) Preference Assessment

An MSWO Preference Assessment allows a teacher to create a hierarchy of the child’s preferences in a very short amount of time. This is an appropriate assessment for children who are able to select preferred items among a large array of items.

However, if a child engages in problem behavior when a preferred toy is taken away, an MSW Preference Assessment should be used for tangible items (i.e., toys). If a child is able to choose highly-preferred items over low-preferred items, but is unable to scan more than two items on a surface, a Paired Stimulus Preference Assessment should be used. If a child is unable to choose highly-preferred items over low-preferred items, or demonstrates a side bias (i.e., selecting items only on one side), a Single Stimulus Preference Assessment or Free Operant Observation should be used.

In an MSWO Preference Assessment, the teacher places an array of items (usually toys or edibles) in front of the child, and allows him or her to select one. After the child plays with or consumes the item, the teacher removes it from the array. Each time the teacher presents the array, this is known as one trial. The teacher repeats trials until there are no items left in the array, or until the child refuses to make any further selections. Typically, the items the child selects during the first few trials are the child’s highest preferred items of the array, and the items the child selects last or refuses to select are the child’s lowest preferred items. The highest preferred items are more likely to serve as reinforcers, or items that will reinforce wanted behaviors. However, keep in mind that not all preferred items function as reinforcers. It is important to (a) perform MSWOs regularly because preferences may change, (b) assess a possible side bias by rotating the items after each trial, and (c) use a combination of likely preferred and non-preferred items to confirm that the child is making choices based on preference. 

Before beginning, you should collect the following materials:
Data collection sheet
An array of 5-7 bite-sized edible items or 5-7 toys

Now you and your child are ready to begin.

1. Sit across from the child at a table or on the floor.
2. Place all items in a straight line within the child’s reach, in order by assigned letter. If the child is unable to wait until your task direction to make a selection, block view of the items with a large book or clipboard.
3. Lift the book or clipboard (if you are blocking the child’s view), and give the task direction, “Pick one” or “Which one do you want?”
4. If the child reaches for more than one item, block access to both items, and repeat the task direction, “Pick one” or “Pick one for now. We’ll pick another one next.”
5. Allow the child to consume the edible item or play with the toy. Block access to the remaining stimuli during this interim.
6. While the child is consuming the edible or playing with the toy, move the leftmost item over to the rightmost position. This will allow you to detect if the child is only choosing from one side.
7. If you are using toys, remove the chosen toy after 15-30 s and put it out of sight. If you are using edibles, wait until the child has finished the edible, and don’t replace it in the array. Thus, for every trial, you will have one less item available than in the previous trial.
8. Repeat steps 4-7 until there are no items left in the array, or until the child refuses to make any further selections.

Now that I’ve finished conducting several MSWO preference assessments, how do I determine the hierarchy of the child’s preferences?

For each item in your array, add up the trial numbers at which the item was selected during each session. For example, if a child chooses apple slices first across three sessions, you would add the trial numbers (1 + 1 + 1) for a total of 3. If a child chooses carrots fifth, sixth, and seventh across three sessions, you would add the trial numbers (5 + 6 + 7) for a total of 18. Items with the lowest totals are the child’s highest preferred items, and items with the highest totals are the child’s lowest preferred items. Thus, in this example, the apple slices are more preferred than carrots. Any items that are not chosen by the child is a session should be assigned the highest available number (e.g., the total number of items). So, if there are six items, and two are not chosen, the number 6 should be assigned to both.

Here is an example of the results of three preference assessment sessions:

In this example, the yo-yo was the child’s highest preferred item, because the sum of the trial numbers (1 + 1 + 1) is 3, which is the lowest total. The toy phone was the child’s lowest preferred item, because the sum of the numbers (6 + 5 + 6) is 17, which is the highest total. Note that the toy phone was not chosen during two sessions—in both sessions, the toy phone was assigned 6, the highest possible number.

Data Sheets:
Multiple Stimulus without Replacement (MSWO): Data Sheet (5 items) 
Multiple Stimulus without Replacement (MSWO): Data Sheet (6 items)
Multiple Stimulus without Replacement (MSWO): Data Sheet (7 items)

To cite this page (APA 6th edition):

• Chazin, K.T. & Ledford, J.R. (2016). Multiple stimulus without replacement (MSWO) preference assessment. In Evidence-based instructional practices for young children with autism and other disabilities. Retrieved from http://ebip.vkcsites.org/multiple-stimulus-without-replacement