Partial Interval, Whole Interval and Momentary Time Sampling in ABA

ABA is built on data. Every goal in your child's plan is measured, and the way a behavior is measured affects what the numbers mean. Three of the most common measurement methods are partial interval recording, whole interval recording and momentary time sampling. This guide explains each one in plain language, with examples, so parents in North Carolina can read their child's data and understand why the ABA team chose a certain method.

Why ABA uses interval recording

Some behaviors are easy to count, such as the number of times a child asks for a snack. Others happen too fast, last too long or blend together, such as humming, staying on task or playing with a peer. Counting every instance is not practical. Interval recording solves this by dividing an observation into short, equal blocks of time and noting whether the behavior happened in each block.

The result is reported as a percentage of intervals. For example, "on task in 80 percent of intervals." It is an estimate, not an exact count, and each method estimates in a different direction.

Key takeaway: Interval data is an estimate. Partial interval tends to overestimate, whole interval tends to underestimate, and momentary time sampling can go either way.

Partial interval recording

With partial interval recording, the observer marks an interval as "yes" if the behavior happens at any point during that interval, even for one second.

Partial interval example

A 10 minute observation is split into 60 intervals of 10 seconds. The behavior being measured is calling out in class. If the child calls out at any moment during an interval, the interval is marked. If the child called out in 15 of 60 intervals, the result is 25 percent.

When partial interval is used

• Behaviors the team wants to decrease, such as calling out, hitting or elopement attempts.
• Behaviors that are brief or happen in quick bursts.

Because one short instance counts as a full interval, this method tends to overestimate how much the behavior happens. For a behavior you want to reduce, overestimating is the cautious choice.

Whole interval recording

With whole interval recording, the interval is marked "yes" only if the behavior happens for the entire interval.

Whole interval example

The behavior is staying seated during a table activity. Intervals are 15 seconds. If the child stays seated for all 15 seconds, the interval is marked. If they stand up for even two seconds, the interval is not marked.

When whole interval is used

• Behaviors the team wants to increase, such as on-task behavior, cooperative play or sitting during meals.
• Behaviors that should continue for a period of time.

Because the behavior must last for the full interval, this method tends to underestimate. For a skill you want to build, underestimating keeps the bar high.

Info: Easy way to remember: partial for "less" behaviors, whole for "more" behaviors.

Momentary time sampling

With momentary time sampling, the observer checks only at the exact moment each interval ends. If the behavior is happening at that moment, the interval is marked.

Momentary time sampling example

A teacher sets a timer to vibrate every 2 minutes during a 30 minute work period. Each time it vibrates, the teacher looks up and notes whether the student is working. If the student was working at 12 of 15 checks, the result is 80 percent.

When momentary time sampling is used

• Longer observations, such as a whole class period.
• Busy settings where the observer is also teaching or caring for the child.
• Behaviors that last a while, such as engagement or independent play.

This method is practical for parents and teachers because it does not require constant watching. It can over or underestimate depending on timing, and very brief behaviors may be missed entirely.

Partial interval vs whole interval vs momentary time sampling

• Partial interval: mark if the behavior happens at any time. Overestimates. Best for behaviors to decrease.
• Whole interval: mark only if the behavior lasts the full interval. Underestimates. Best for behaviors to increase.
• Momentary time sampling: mark if the behavior is happening at the end of the interval. Can go either way. Best for long observations and busy settings.

Other ways ABA measures behavior

Interval methods are only part of the picture. Depending on the goal, an ABA team may also use:

• Frequency: counting each time a behavior happens.
• Rate: frequency divided by time, such as requests per hour.
• Duration: how long a behavior lasts, such as the length of a tantrum.
• Latency: how long it takes to start after an instruction.
• ABC data: what happens before and after a behavior, often recorded with an ABC chart.

You can read more in our guide to how ABA therapists use data to measure progress.

How parents can read interval data

1. Check the method. Ask whether the graph uses partial, whole or momentary time sampling.
2. Check the direction. For behaviors to reduce, the line should trend down. For skills to build, it should trend up.
3. Look at the trend, not one day. A single high or low point is normal. Patterns across weeks matter more.
4. Compare settings. Data from home and school may differ, and both are useful.
5. Ask questions. Your child's team should be glad to walk you through any graph.

Success tip: If you want to help collect data at home, momentary time sampling with a phone timer is often the easiest place to start.

Data collection at Sunny Skies ABA

Sunny Skies ABA provides ABA therapy at home and at school across North Carolina, with a primary focus on Raleigh. Data is collected during every session, and a BCBA reviews it regularly to decide when to move to the next goal, change a strategy or adjust support. Because sessions happen in real settings, the data reflects how your child is doing in everyday life. Families receive updates and guidance on simple ways to track progress at home.

Frequently asked questions

What is the difference between partial and whole interval recording?

Partial interval counts an interval if the behavior happens at any point. Whole interval counts it only if the behavior lasts the entire interval.

Does partial interval recording overestimate or underestimate behavior?

It usually overestimates, because even a very brief behavior counts as the full interval.

Why use momentary time sampling instead of counting?

It is practical for long observations and busy settings, since the observer only needs to look at set moments rather than watch constantly.

Is ABA therapy covered by insurance in North Carolina?

Yes. ABA for children with autism is covered by most insurance payors in North Carolina, including NC Medicaid plans. See the plans Sunny Skies ABA accepts on our insurance page.

See clear, data-driven progress

Sunny Skies ABA supports children and young adults with autism, ages 2 to 21, through in-home and school-based ABA therapy across North Carolina. Book a free consultation to learn how we track and share your child's progress.

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