Free · 2026 · ABA data collection for the RBT exam Interval recording: partial interval, whole interval and momentary time sampling, with a scoring trainer
Interval recording is a discontinuous way to measure behavior in ABA: you divide an observation into equal intervals, often 10 seconds, and score each interval as occurred (+) or not occurred (−) instead of counting every instance. There are three methods. Partial interval recording scores an interval if the behavior happens at any point in it, so it tends to overestimate. Whole interval recording scores it only if the behavior lasts the entire interval, so it tends to underestimate. Momentary time sampling (MTS) scores it only if the behavior is happening at the moment the interval ends, and its error can go either way. All three are reported as a percentage of intervals. They're task A.2 on the 3rd edition RBT Test Content Outline and task 2 of the 2026 RBT competency assessment. Below: the facts, a free trainer with 8 timelines to score each way, and 12 practice questions with answers.
- Partial intervalOverestimatesScore + if the behavior happens at any point in the interval.
- Whole intervalUnderestimatesScore + only if the behavior lasts the entire interval.
- Momentary time samplingOver or underScore + only if the behavior is happening at the moment the interval ends.
Continuous vs discontinuous measurement
Continuous measurement records every instance of a behavior during the observation: how many times (frequency and rate), how long (duration), how soon after an instruction (latency) and how long between responses (interresponse time, or IRT). It is the most complete picture, but it needs a behavior with a clear start and end and someone free to watch the whole time.
| Measure | What it records | Best for | Example |
|---|---|---|---|
| Frequency (count) | Every occurrence | Behaviors with a clear start and end | 9 requests for help in a session |
| Rate | Count divided by time | Comparing sessions of different lengths | 18 hand raises in 30 min = 0.6 per minute |
| Duration | How long each episode lasts (total or mean) | Long behaviors: tantrums, on-task, play | Tantrums of 4, 6 and 11 min: total 21, mean 7 min |
| Latency | From the instruction to the start of the response | Slow starts, following directions | "Line up" given; moving after 40 s |
| Interresponse time (IRT) | From the end of one response to the start of the next | Pacing of a behavior | 25 s between one bite ending and the next starting |
Discontinuous measurement samples the behavior instead: it records whether the behavior happened in an interval, or at a moment, so some instances go unrecorded. It trades accuracy for practicality. It works for behaviors that are very frequent or have no clear start and end, and it lets an RBT collect data while teaching or watching a group.
| Method | Score + when | Bias | Good for |
|---|---|---|---|
| Partial interval | The behavior happens at any point in the interval | Overestimates | Behaviors to decrease; brief, high-rate behaviors |
| Whole interval | The behavior lasts the entire interval | Underestimates | Behaviors to increase, such as on-task or engagement |
| Momentary time sampling | The behavior is happening at the moment the interval ends | Over- or underestimates (no fixed direction) | Long-lasting behaviors, groups, or when you can only look up at set moments |
The biases are why each method has its usual job. Partial interval inflates a behavior, so a drop in a behavior you want less of is real when you see it. Whole interval shrinks a behavior, so on-task time won't look better than it is. In a 1975 study that compared the three against continuous records, whole interval consistently underestimated and partial interval overestimated, while momentary time sampling erred in both directions about equally, and all three got more accurate with shorter intervals. Your supervising BCBA picks the method and the interval length; the RBT records as the plan says.
How to calculate percentage of intervals, rate and mean duration
Interval data are summarized as a percentage of intervals, not a count of behaviors. Task A.6 also asks for rate and mean duration.
Percentage of intervals
Intervals scored ÷ total intervals × 100
5 minutes of 10-second intervals is 30 intervals. 12 scored + gives 12 ÷ 30 × 100 = 40%.
Rate
Count ÷ observation time
18 hand raises in 30 minutes is 0.6 per minute (36 per hour).
Mean duration
Total duration ÷ number of episodes
Tantrums of 4, 6 and 11 minutes: 21 ÷ 3 = 7 minutes each, on average.
Interval recording trainer: score it yourself
Each observation is one minute, split into six 10-second intervals. The orange bar shows when the behavior is happening; press Watch it to play the minute. Pick a method, tap each interval to score it + or −, then check: you'll see the right score for every interval, why, and how far the method's percentage lands from the true duration. All three, side by side scores the same minute every way.
Observation 1 of 8 · six 10-second intervals
Hand flapping (brief bursts) · a behavior to decrease
Behavior happening
Partial interval: Score + if the behavior happens at any point in the interval. Tap each interval to score it + or −, then check.
Measurement practice: 12 questions with answers
Scoring rules, which way each method is biased, and the calculations the RBT exam asks for. The reason shows after each answer.
Question 1 of 12 · 0 right so far
The BCBA wants a conservative estimate that won't overstate progress on on-task behavior, a behavior the plan aims to increase. Which interval method fits?
Interval recording on the RBT exam
On the 3rd edition RBT Test Content Outline, Data Collection and Graphing is 13 of the 75 scored questions. Continuous measurement is task A.1, discontinuous measurement (partial interval, whole interval, momentary time sampling) is A.2, and calculating rate, mean duration and percentage is A.6. Expect short scenarios that ask how an interval is scored, which method fits a behavior, or which way a method is biased.
- Partial interval overestimates; whole interval underestimates. Swapping them is the most common miss.
- Momentary time sampling looks only at the moment the interval ends, not at the whole interval.
- Latency starts at the instruction; IRT starts at the end of the previous response.
- Duration answers "how long"; frequency answers "how many". Read which one the question asks for.
- Use rate, not raw count, when sessions are different lengths.
- Interval data are reported as a percentage of intervals, not as a count of behaviors.
On the 2026 competency assessment
Before certification, an assessor watches you measure behavior, with a client or in role-play. Task 1 is continuous measurement (count, duration, latency, IRT) and task 2 is discontinuous measurement: you score partial interval, whole interval and momentary time sampling live with a timer and give the percentage of intervals. Our RBT competency assessment guide has a role-play for each of the 19 tasks.
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Interval recording FAQ
What is interval recording in ABA?
Interval recording is a discontinuous measurement method: the observation is split into equal intervals (often 10 seconds) and each interval is scored as occurred (+) or not occurred (−), instead of counting every instance. The three methods are partial interval recording, whole interval recording and momentary time sampling, and the result is reported as a percentage of intervals.
What is the difference between partial and whole interval recording?
Partial interval recording scores an interval if the behavior happens at any point in it, so it tends to overestimate the behavior. Whole interval recording scores an interval only if the behavior lasts the entire interval, so it tends to underestimate it. Partial interval suits behaviors to decrease and whole interval suits behaviors to increase.
What is momentary time sampling?
Momentary time sampling (MTS) scores an interval only if the behavior is happening at the moment the interval ends. What happens during the rest of the interval doesn't count. It can overestimate or underestimate, and it suits long-lasting behaviors and observing a group, because the observer only has to look up at set moments.
Does partial interval recording overestimate or underestimate?
It overestimates. One brief instance scores the whole interval, so the percentage of intervals is at or above the real share of time the behavior took. Whole interval recording does the opposite and underestimates.
How do you calculate the percentage of intervals?
Divide the intervals scored + by the total number of intervals and multiply by 100. For example, 7 of 20 intervals scored is 7 ÷ 20 × 100 = 35%. Report interval data this way, not as a count of behaviors.
What is the difference between continuous and discontinuous measurement?
Continuous measurement records every instance of the behavior during the observation: frequency, rate, duration, latency and interresponse time. Discontinuous measurement samples the behavior in intervals or at moments, so some instances aren't recorded: partial interval, whole interval and momentary time sampling.
Who decides which measurement method to use?
The supervising BCBA chooses the measure and the interval length and writes them into the plan. The RBT records the data as written, live, with a timer, and never fills in intervals afterward.
Sources, checked October 28, 2026: BACB: RBT Test Content Outline (3rd ed.) · BACB: RBT Initial Competency Assessment (2026) · Powell, Martindale & Kulp (1975): An evaluation of time-sample measures of behavior, JABA · Cooper, Heron & Heward: Applied Behavior Analysis (3rd ed., 2020). For exam study, not clinical guidance: your supervising BCBA chooses the measurement method, and RBTs record data as the plan says.