Partial vs. Whole Interval vs. Momentary Time Sampling in ABA

Partial interval recording, whole interval recording, and momentary time sampling are the three discontinuous measurement methods RBTs use. Each one splits an observation into intervals, but they score those intervals differently, so each one tends to overestimate or underestimate behavior in its own way. This guide compares them side by side with examples so you can pick the right one and answer exam questions with confidence.

What Is Discontinuous Measurement?

Discontinuous measurement records a sample of behavior instead of every occurrence. It is useful when behavior is hard to count, very frequent, or when you cannot watch continuously. Using discontinuous measurement is task A.2 on the RBT Test Content Outline (3rd ed.). If you need every instance, use continuous measurement instead. For a full overview, see Discontinuous Measurement in ABA.

Comparison at a Glance

Method	Score the interval when…	Tends to	Best for
Partial interval recording	The behavior occurs at any point during the interval	Overestimate behavior	Behaviors you want to decrease
Whole interval recording	The behavior occurs for the entire interval	Underestimate behavior	Behaviors you want to increase, like on-task behavior
Momentary time sampling (MTS)	The behavior is occurring at the exact moment the interval ends	Over- or underestimate (less biased overall)	Ongoing behaviors when you cannot watch the whole time

Partial Interval Recording

In partial interval recording, you mark an interval if the behavior happens at any time during it, even once and even briefly. Because one quick instance scores the whole interval, partial interval recording tends to overestimate how much the behavior occurs.

Example: During a 10-minute session split into 30 ten-second intervals, you mark every interval in which the learner flaps their hands at least once.

Whole Interval Recording

In whole interval recording, you mark an interval only if the behavior happens for the entire interval. If the learner is off task for even a second, the interval is not scored. That is why whole interval recording tends to underestimate behavior.

Example: You record whether a student stays seated for each full 15-second interval during independent work.

Momentary Time Sampling (MTS)

With momentary time sampling, you only look at the moment each interval ends and record whether the behavior is happening right then. It is easy to use while doing other things, but behavior that happens between checks is missed.

Example: A timer vibrates every 2 minutes. Each time, the RBT glances up and records whether the student is engaged in the activity.

Which One Should You Use?

• Your BCBA chooses the measurement method in the plan. RBTs implement it as written.
• Use partial interval to track behaviors you want to reduce, since overestimating is the safer error.
• Use whole interval for behaviors you want to increase, since underestimating is the safer error.
• Use MTS for ongoing behaviors or when you are running other programs at the same time.
• Shorter intervals give more accurate data. Long intervals make over- and underestimation worse.

Exam tip: “Which method might overestimate behavior?” Partial interval. “Which might underestimate behavior?” Whole interval. “Which records behavior only at the end of the interval?” Momentary time sampling.

Need a sheet for your next session? Download our free interval recording data sheet, which works for partial interval, whole interval, and MTS.

Frequently Asked Questions

What is the difference between partial interval and whole interval recording?

Partial interval recording scores an interval if the behavior occurs at any point during it. Whole interval recording scores it only if the behavior lasts the entire interval.

Which measurement method might overestimate behavior?

Partial interval recording tends to overestimate behavior because a single brief occurrence scores the whole interval.

Which measurement method might underestimate behavior?

Whole interval recording tends to underestimate behavior because any break in the behavior means the interval is not scored.

What is momentary time sampling?

A discontinuous method where you record whether the behavior is occurring at the exact moment each interval ends.

Why do shorter intervals give better data?

Shorter intervals sample behavior more often, which reduces the over- and underestimation that comes with longer intervals.