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Partial interval vs whole interval vs momentary time sampling is the difference between scoring any occurrence, full-interval occurrence, or occurrence at a sample instant. The BACB RBT Test Content Outline (3rd ed.) places all three under task A.2, discontinuous measurement.
Quick Comparison#
This table shows the rule difference an RBT candidate has to notice before scoring an interval.
| Criterion | Partial interval | Whole interval | Momentary time sampling |
|---|---|---|---|
| Definition | Scores whether the response occurred at least once in the interval. | Scores whether the response occurred for the entire interval. | Scores whether the response occurred at one planned sample moment. |
| What is measured | Sampled occurrence during an interval. | Sampled sustained occurrence across an interval. | Sampled occurrence at the check point. |
| When used in exam stems | The wording says any time, at least once, or occurred during. | The wording says whole time, full interval, or start to finish. | The wording says when the timer beeps, at the endpoint, or at the sample moment. |
| Error pattern | Can overestimate duration because one brief response scores yes. | Can underestimate occurrence because one gap scores no. | Can miss behavior before or after the sample instant. |
| Exam trap | Treating a yes interval as an exact count or exact duration. | Scoring yes because the response happened for most of the interval. | Watching the whole interval instead of checking the planned instant. |
For the broader skill page, review discontinuous measurement aba after this comparison. That guide connects these three rules to the rest of task A.2 and separates interval sampling from continuous measurement.
The glossary hub for aba terms is useful when this page raises another behavior-analytic term. It keeps measurement, reinforcement, assessment, reduction, documentation, and ethics vocabulary in one index.
Same Grid Scored Three Ways#
The grid below uses the same observation period for each method, so the score changes only because the rule changes.
| Interval | What happened during the interval | True duration sample | Partial interval | Whole interval | Momentary time sampling |
|---|---|---|---|---|---|
| 1 | Response present start to finish | 100% | Yes | Yes | Yes |
| 2 | Response present only near the start | 30% | Yes | No | No |
| 3 | Response appears during the last 10% and remains present at the endpoint | 10% | Yes | No | Yes |
| 4 | Response absent throughout | 0% | No | No | No |
| 5 | Response present through the middle, then stops | 60% | Yes | No | No |
| 6 | Response present only in the middle | 40% | Yes | No | No |
| 7 | Response begins halfway through and remains present to the end | 50% | Yes | No | Yes |
| 8 | Response present for all but a brief gap | 90% | Yes | No | Yes |
From the same eight intervals, partial interval scores seven yes intervals, whole interval scores one yes interval, and momentary time sampling scores four yes intervals. True duration across the rows averages 47.5%, but the partial-interval score is 87.5%, the whole-interval score is 12.5%, and the momentary score is 50%.
Those differences are not contradictions. Each rule asks a different sampling question, which is why an RBT must follow the written measurement rule rather than choosing the method that gives the most favorable percentage. In services, the supervising BCBA's written plan controls the data-collection method.
The BACB Initial Competency Assessment Packet, 2026 also lists discontinuous measurement with partial and whole interval and momentary time sampling. That packet supports why the same distinction matters for technician skill checks, while the Test Content Outline states the scored-exam task.
Decision Rule For Exam Questions#
This decision table turns the comparison into a fast selection rule for A.2 scenarios.
| Stem clue | Choose | Why |
|---|---|---|
| The behavior happened once, briefly, or at any point in the interval. | Partial interval | One occurrence is enough to score the interval yes. |
| The behavior lasted from the interval start through the interval end. | Whole interval | The response must be present for the full interval. |
| The observer checks only when a timer sounds or a sample point arrives. | Momentary time sampling | Earlier or later behavior does not decide that sample. |
| The stem asks for exact count, latency, duration, or IRT. | Not one of these three | Those are continuous measurement procedures, not A.2 interval samples. |
| The stem asks for completed work after the session. | Not one of these three | A lasting product belongs to permanent-product recording. |
The single-topic page on momentary time sampling is the best next step when sample-point wording is the part that feels unclear. It focuses on endpoint checks, group observations, and why momentary scores can miss behavior that happened earlier.
Use whole interval recording when a question emphasizes sustained behavior from start to finish. Use partial interval recording when the confusing point is why one brief occurrence can score the entire interval yes.
Practice Allocation For This Page#
This table separates official scored-exam weights from this article's practice set.
| Measure | Count | Source or purpose |
|---|---|---|
| Official Domain A scored questions | 13 | RBT Test Content Outline (3rd ed.) |
| Official Domain A share | 17% | RBT Test Content Outline (3rd ed.) |
| This page's practice items | 5 | Original practice for this comparison |
| Tags used below | 5 A.2 items | Page-level drill, not an official exam allocation |
After these focused items, the rbt practice test data collection and graphing mixes A.2 with graphing, calculation, permanent product, observable descriptions, and data-quality tasks. That is the better place to test whether the rule still holds when distractors come from the rest of Domain A.
Practice Questions#
These original questions test task A.2 from the RBT Test Content Outline (3rd ed.): "Implement discontinuous measurement procedures (e.g., partial & whole interval, momentary time sampling)."
1. During table work, Ana taps the desk once near the middle of a 30-second interval. The sheet says a brief occurrence during the interval earns a yes mark. Which method fits?
A Correct. Partial interval scoring marks yes when the response occurs at least once during the interval.
B Whole interval scoring would require the response to last from the interval start through the interval end.
C Momentary sampling would check whether the response is occurring at the planned sample instant.
D Duration timing measures how long behavior lasts rather than whether an interval met a sampled rule.
2. A timer starts for a 20-second observation. Ben is on task for 18 seconds, looks away for 2 seconds, then the interval ends. The sheet requires presence for the full interval. What mark fits?
A Most of the interval is not enough when the scoring rule requires the full interval.
B Correct. Whole interval scoring is no when the response is absent for part of the interval.
C Endpoint wording would matter for momentary sampling, not for a full-interval rule.
D The timer did not change; the interval is scored by the stated rule.
3. During group instruction, the observer checks Chris only when each minute beep sounds. Chris was talking earlier, but is quiet at the beep. How should that sample be scored?
A Earlier behavior does not score a sample that is based on the planned check point.
B Brief behavior during the interval would matter for a different interval rule.
C Correct. Momentary time sampling scores the behavior status at the planned instant.
D The score applies to this sample; other intervals still depend on their own check points.
4. In one interval, Dana hums at the start, stops, hums in the middle, and is quiet at the final beep. Which rule would still score that interval yes?
A Whole interval would be no because the response did not last for the full interval.
B Momentary sampling would be no because the response was absent at the final beep.
C Event recording would count responses instead of assigning one interval score.
D Correct. Partial interval scoring is yes because the response occurred during the interval.
5. A data sheet says to check engagement only when a vibrating timer signals every interval. Eli is engaged at the signal, although he was off task earlier. Which method is shown?
A Correct. Momentary sampling uses the planned signal point to decide the score.
B Partial interval would score any occurrence during the interval, not just the signal point.
C Whole interval would require engagement across the entire interval.
D Product recording measures a lasting outcome after behavior occurs.
FAQ
What is the main difference between partial and whole interval recording?
Partial interval recording scores yes if the behavior happens at least once during the interval. Whole interval recording scores yes only if the behavior lasts for the full interval.
How is momentary time sampling different from partial interval recording?
Momentary time sampling checks the behavior at one planned instant, such as the endpoint. Partial interval recording watches the whole interval for any occurrence.
Which method overestimates behavior?
Partial interval recording can overestimate duration because a brief response can make the whole interval yes. Whole interval recording can underestimate occurrence because any gap makes the interval no.
Are these methods on the RBT exam?
Yes. The RBT Test Content Outline (3rd ed.) lists partial interval, whole interval, and momentary time sampling under A.2, which is part of Data Collection and Graphing.
Should an RBT choose the method during real services?
No. This page teaches exam discrimination. During services, an RBT follows the supervising BCBA's written data-collection plan and asks for clarification when the rule is unclear.