A.2 Discontinuous measurement
Discontinuous measurement records a sample of behavior instead of every occurrence. The observation is divided into equal intervals, and each interval is scored by a rule: partial interval, whole interval or momentary time sampling. The results are estimates, reported as the percentage of intervals scored, and each procedure has a known pattern of error.
What the outline says
Task A.2 in content area A, Data Collection and Graphing (13 of the 75 scored questions): "Implement discontinuous measurement procedures (e.g., partial & whole interval, momentary time sampling)."
Why sample instead of count
Some behaviors are hard to measure continuously. Rocking, humming or hand-flapping may happen so often, or flow so continuously, that you cannot tell one instance from the next. In other situations you are teaching a group and cannot watch one client every second. Discontinuous procedures solve these problems by recording whether the behavior met a rule during each interval instead of capturing every occurrence.
The price is accuracy: discontinuous data are estimates. They do not give a count, a duration or a latency. They give the percentage of intervals in which the behavior was scored. Your supervisor chooses the procedure and interval length with these limits in mind; your job is to apply the scoring rule exactly.
Setting up
- Know the operational definition and the procedure the plan calls for.
- Know the interval length (for example 10 seconds, 1 minute, 5 minutes) and the total observation time, so you know how many intervals there are. A 10-minute observation with 15-second intervals has 600 ÷ 15 = 40 intervals.
- Use a timer, vibrating device or data app that signals the end of each interval, so your eyes can stay on the client.
- Some data sheets build in a recording period, such as "observe 10 s, record 5 s." You watch during the 10-second interval and mark the sheet during the 5 seconds after it.
Partial interval recording
Score the interval if the behavior occurs at any time during it, even for a second. Once it has occurred, the interval is scored; more occurrences in the same interval do not change anything. A behavior that starts in one interval and continues into the next is scored in both.
Because a brief occurrence scores a whole interval, partial interval recording tends to overestimate how much of the time the behavior occurred. It also cannot show how many times the behavior happened, and once every interval is scored (100%) it cannot show further increases. It is often used for behaviors targeted for reduction and for behaviors that happen too quickly to count.
Whole interval recording
Score the interval only if the behavior continues for the entire interval. Any break, even a short glance away, means the interval is not scored. If a child plays from the start of the first 10-second interval for 25 seconds, intervals 1 and 2 are scored and interval 3 is not, because play lasted only 5 seconds of it.
Because time spent in the behavior during unscored intervals is lost, whole interval recording tends to underestimate how much of the time the behavior occurred. It suits behaviors that can last for long stretches and that the team wants to increase, such as on-task behavior, engagement or cooperative play. Brief behaviors such as hitting or saying a word would almost never fill an interval.
Momentary time sampling
Look at the client at the moment each interval ends and score the interval only if the behavior is occurring at that moment. What happened earlier in the interval does not count. A client who was out of their seat for 50 seconds but seated when the timer signals is not scored for that interval.
Because you only need to look at set moments, momentary time sampling fits busy settings and longer observations, and a group version (sometimes called a planned activity check) lets you scan several clients at each check. Its weakness is that it can miss behavior between checks, especially brief behavior, and it can overestimate or underestimate depending on when the behavior happens relative to the checks. If momentary data show 0% but people regularly see the behavior, tell your supervisor.
Summarizing and keeping data honest
Percentage of intervals = intervals scored ÷ total intervals observed × 100. With 12 of 30 intervals scored, the result is 40% of intervals. Report it as a percentage of intervals, not as a percentage of time or a count. Partial interval data of 80% do not mean the behavior lasted 80% of the session.
Shorter intervals generally give a closer estimate for all three procedures, which is one reason you should not lengthen intervals on your own. If you miss an interval or a check, mark it as not observed; do not guess or copy the previous result. If a procedure is too hard to carry out or the data do not match what you are seeing, keep following the plan and tell your supervisor.
Examples and non-examples
| Example | Non-example |
|---|---|
| Using 10-second partial interval recording, an RBT marks an interval because the client screamed briefly in it, and marks it only once even though the client screamed three times. | The RBT writes "3" in the interval box; interval recording does not count occurrences. |
| Using 20-second whole interval recording, an RBT scores an interval because the student worked for the full 20 seconds. | The RBT scores an interval in which the student worked for 18 seconds and looked away for 2 seconds. |
| Using 5-minute momentary time sampling, the RBT glances at the client when the vibrating timer goes off and records whether the client is engaged at that moment. | The RBT scores an interval because the client was engaged earlier in it but not at the moment of the check. |
Common mistakes
- Mixing up the scoring rules. Partial: any time in the interval. Whole: the entire interval. Momentary: only at the moment the interval ends.
- Reporting interval data as a count or as a percentage of time. The result is a percentage of intervals.
- Forgetting that a behavior crossing an interval boundary is scored in both intervals under partial interval recording.
- Changing the interval length or switching procedures without the supervisor. Data collected in different ways are not directly comparable.
- Filling in missed intervals from memory. Mark them as not observed.
How it's tested
Questions usually describe what an RBT does during intervals and ask which procedure it is, or describe a behavior inside an interval and ask how it should be scored. Learn which procedure tends to overestimate (partial interval), which tends to underestimate (whole interval), and which can go either way (momentary time sampling). Expect a simple calculation of percentage of intervals, sometimes after first working out how many intervals there are.
Practice questions for task A.2
10 of our 32 questions on this task. The rest are in the Data Collection and Graphing practice sets and the mock exams.
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Question 1Which of these is a discontinuous measurement procedure?
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D: Momentary time sampling. Discontinuous procedures record a sample of the behavior instead of every occurrence. Momentary time sampling looks at the behavior only at the moment each interval ends.
- A: Frequency recording counts every occurrence during the observation period, so it is continuous.
- B: Duration recording times every occurrence from start to end, so it is continuous.
- C: Interresponse time recording times every gap between responses, so it is continuous.
Task A.2 · 40-hour curriculum section C
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Question 2Data from partial interval, whole interval and momentary time sampling procedures are usually summarized as:
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A: the percentage of intervals scored. Each interval is scored as an occurrence or a nonoccurrence. The summary is the number of scored intervals divided by the total number of intervals, times 100.
- B: Responses per minute is rate, which needs a count of every response; interval procedures do not count responses.
- C: Average length per response is mean duration, which requires timing each occurrence.
- D: Time from cue to response is latency, a continuous measure.
Task A.2 · 40-hour curriculum section C
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Question 3At an adult day program, an RBT checks every 5 minutes whether a client is working on their assigned task at that exact moment and marks yes or no. Which procedure is this?
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D: Momentary time sampling. Looking at the behavior only at the moment each interval ends and recording whether it is occurring then is momentary time sampling.
- A: Partial interval recording would score an interval if the behavior happened at any point during it, which requires watching throughout.
- B: Whole interval recording would score an interval only if the client worked during the entire interval.
- C: Duration recording would time how long the client worked.
Task A.2 · 40-hour curriculum section C
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Question 4A classroom RBT uses 20-second intervals and marks an interval only if the student kept working on the assignment for the whole 20 seconds. Which procedure is this?
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D: Whole interval recording. Scoring an interval only when the behavior occurs throughout the entire interval is whole interval recording.
- A: Partial interval recording would score the interval if the student worked at any point during it.
- B: Momentary time sampling would check only at the end of each interval.
- C: Latency recording would time how long the student took to begin after an instruction.
Task A.2 · 40-hour curriculum section C
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Question 5During a 60-second interval, a client hums for 5 seconds in the middle of the interval and is quiet at all other times. How would each procedure score this interval for humming?
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C: Partial interval would score it; whole interval and momentary time sampling would not. Partial interval recording scores any occurrence in the interval, so it scores this one. Whole interval recording needs the behavior for the entire interval, and momentary time sampling needs it at the moment the interval ends; neither condition was met.
- A: Whole interval recording needs humming throughout all 60 seconds, and partial interval recording would score any occurrence.
- B: The client was quiet at the end of the interval, so momentary time sampling would not score it.
- D: Momentary time sampling looks only at the end of the interval, when the client was quiet.
Task A.2 · 40-hour curriculum section C
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Question 6Which discontinuous procedure tends to underestimate how much of the time a behavior actually occurs?
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A: Whole interval recording. Whole interval recording leaves an interval unscored if the behavior stops even briefly, so time spent in the behavior during unscored intervals is lost and the percentage is usually lower than the true value.
- B: Partial interval recording tends to overestimate, because brief occurrences count for the whole interval.
- C: Momentary time sampling can over- or underestimate; it has no built-in tendency to underestimate.
- D: A planned activity check is a group form of momentary time sampling and shares its pattern of error.
Task A.2 · 40-hour curriculum section C
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Question 7An RBT is teaching a small group, and the plan uses momentary time sampling for one student's engagement. What does the RBT need to do to collect these data?
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D: Look when each interval ends and mark if engaged. Momentary time sampling only requires a look at the moment each interval ends, so the RBT can keep teaching between checks. A vibrating timer or app cue helps the RBT check at the right moment.
- A: Watching throughout each interval and marking any occurrence is partial interval recording.
- B: Timing each period of engagement is duration recording.
- C: Counting each time engagement begins is frequency recording.
Task A.2 · 40-hour curriculum section C
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Question 8An RBT uses partial interval recording with 30 intervals. Hitting is marked in 12 of them. What should the RBT report?
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C: 40% of intervals. Divide scored intervals by total intervals and multiply by 100: 12 ÷ 30 = 0.40, or 40% of intervals.
- A: 12 is the number of scored intervals, not a percentage.
- B: 18 is the number of intervals without hitting, not a percentage.
- D: 60% would mean 18 of the 30 intervals were scored.
Task A.2 · 40-hour curriculum section C
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Question 9A 10-minute observation is divided into 15-second intervals. The behavior is scored in 10 intervals. What percentage of intervals is that?
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C: 25%. 10 minutes is 600 seconds, and 600 ÷ 15 = 40 intervals. Then 10 ÷ 40 = 0.25, or 25% of intervals.
- A: 10 is the number of scored intervals, not the percentage.
- B: 15 is the interval length in seconds, not the percentage.
- D: 40 is the total number of intervals, not the percentage.
Task A.2 · 40-hour curriculum section C
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Question 10Partial interval data show that a client hit others in 60% of intervals. A caregiver asks how many times the client hit. What is the accurate answer?
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C: Interval data cannot give that number. Interval procedures record whether the behavior occurred in each interval, not how many times. A count would need frequency recording.
- A: 60% is a percentage of intervals, not a count of hits.
- B: An interval may contain one hit or several; the data show only that at least one occurred.
- D: Partial interval recording does not measure how long hitting lasted, and it tends to overstate time spent in the behavior.
Task A.2 · 40-hour curriculum section C
Answer every question to see your score.
Key terms
| Discontinuous measurement | Discontinuous measurement samples behavior during parts of an observation, using intervals, so it gives an estimate rather than a record of every occurrence. |
|---|---|
| Partial interval recording | Partial interval recording scores an interval if the target behavior occurs at any time during that interval, however briefly. |
| Whole interval recording | Whole interval recording scores an interval only if the target behavior occurs throughout the entire interval, without stopping. |
| Momentary time sampling | Momentary time sampling scores an interval only if the target behavior is occurring at the exact moment the interval ends. |
| Percentage | A percentage is a ratio expressed as parts per 100: the number of occurrences divided by the total, multiplied by 100. |
| Continuous measurement | Continuous measurement records every occurrence of the target behavior during the entire observation period, using measures such as frequency, rate, duration, latency or interresponse time. |
| Frequency | Frequency is the number of times a behavior occurs during an observation period, recorded by counting every occurrence from start to finish. |