# How do I run a preference assessment in ABA?

> Why preferences change, the main formats (paired stimulus, MSWO, free operant), and quick in-session checks.

URL: https://theautismkit.com/guides/preference-assessments
By The Autism Kit team · Updated 2026-09-27

**Short answer:** A preference assessment identifies items or activities a client likes, which can then be tested as reinforcers. Common formats are paired stimulus (two items at a time), multiple stimulus without replacement (MSWO, several items at once), and free operant (watching what the client engages with). Preferences change, so brief checks before and during sessions matter.

**Key takeaways**
- Preference assessments find **what the client likes**.
- Formats: **paired stimulus**, **MSWO** and **free operant**.
- **Preferences change**, so check often.
- Confirm reinforcement by **watching the effect on behavior**.

## Why run preference assessments?

Reinforcement only works if the consequence actually matters to the client. Preferences shift with mood, time of day and satiation. Conducting preference assessments is part of RBT training in the 2026 curriculum.[3]

## What are the main formats?

| Format | How it works | Good for |
| --- | --- | --- |
| Paired stimulus | Two items at a time; every pair presented | Clear rankings; clients who can choose between two |
| MSWO | Several items at once; chosen item isn't replaced | Quicker rankings of several items |
| Free operant | Items available; record time engaged with each | Clients who find choosing hard; no items removed |
| Brief check | Offer 2 or 3 options before a task | Every session |

The paired-stimulus format was evaluated by Fisher and colleagues, and the MSWO by DeLeon and Iwata.[1][2]

## How do I run an MSWO?

1. Put 5 to 8 items in a row in front of the client.
2. Say "Pick one."
3. Let them engage briefly with the chosen item.
4. Remove it, rearrange the rest, and repeat until all are chosen or none are.
5. Rank items by order of selection. Repeating the array across sessions gives more reliable rankings.

**Offer choice with pictures.** A picture choice board lets clients choose a reinforcer quickly and builds communication at the same time.

## What else should I watch for?

**Try:**
- Checking preferences at the start of every session
- Rotating items to avoid satiation
- Noticing assent: does the client still want this?

**Skip:**
- Using the same reinforcer for months
- Assuming yesterday's favorite still works

**Include caregivers.** Families know what their child loves. Ask them, then confirm with a quick assessment.

## What can I do this week?

- [ ] Run an MSWO with one client
- [ ] Add a brief choice check to session openings
- [ ] Ask caregivers for 5 new preferred items

Read next: [How do I use a token economy in ABA?](https://theautismkit.com/guides/token-economy-aba)

## Common questions

### Is a preferred item always a reinforcer?

Not necessarily. Preference assessments identify likely reinforcers. You confirm reinforcement when the item increases the behavior it follows.

### How often should I run preference assessments?

Brief checks at the start of each session are common, with more formal assessments when motivation drops or periodically.

### Can I use pictures instead of items?

Sometimes, if the client understands pictures as representing items. Picture choice boards are a practical way to offer choices in session.

## Sources

1. Fisher W, et al. A comparison of two approaches for identifying reinforcers for persons with severe and profound disabilities. Journal of Applied Behavior Analysis, 1992. https://doi.org/10.1901/jaba.1992.25-491
2. DeLeon IG, Iwata BA. Evaluation of a multiple-stimulus presentation format for assessing reinforcer preferences. Journal of Applied Behavior Analysis, 1996. https://doi.org/10.1901/jaba.1996.29-519
3. Behavior Analyst Certification Board: RBT 2026 40-hour training requirements and curriculum outline. https://www.bacb.com/wp-content/uploads/2023/12/2026-RBT-40-Hour-Training-Curriculum-260313-a.pdf

General guidance, not a diagnosis or treatment plan. Talk with your pediatrician or a developmental specialist about your child's care.