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This is the plain-language version. Same content, written for a quick read.
Some behaviors don't have a clear start and stop. Some happen too often to count one at a time. Interval recording lets you measure these. Knowing which method to use (and what each one measures) keeps you from taking data that looks sharp but answers the wrong question.
Some behaviors are hard to count in clear units. On-task time. Self-stim that comes and goes. Long tantrums. Frequency counts don't catch these well.
Interval recording is a useful other way. Split a watching window into equal time chunks (intervals). Then mark whether the behavior happened during, throughout, or at the moment of each one.
All interval methods trade some accuracy for being doable. None of them tell you exactly how much of the time a behavior happened. They estimate. Knowing which estimate you are making, and how to read it, is what makes the data useful.
Mark the interval only if the behavior happened for the WHOLE interval.
Best for: behaviors you want to see last, on-task time, reading, staying in the seat.
What it tends to do: under-estimates the true percent of time. One break makes you miss the whole interval.
Example: 10-second intervals during independent work. Mark "+" only if the student was on-task for all 10 seconds. A student who drifts at second 9 gets a "-" for that interval.
Use when: you care about length. You want an estimate that errs on the low side (a conservative estimate).
Mark the interval if the behavior happened at ANY point during the interval. Even for a moment.
Best for: behaviors you want to see less of, disruptions, off-task, stims.
What it tends to do: over-estimates the true percent of time. A 1-second behavior in a 30-second interval still scores the whole interval.
Example: 30-second intervals during group lesson. Mark "+" if the student called out at any point during those 30 seconds.
Use when: you want to catch the behavior. You care whether it happened at all, not for how long.
Mark the interval based on what the student is doing at the exact moment the interval ends. (Or begins, pick one and be the same about it.)
Best for: behaviors that happen often. Data on a group. Times when you can't watch the student all the time.
What it tends to do: doesn't really over- or under-estimate. It samples across the watching window in a fair way. It gives a fair estimate of true duration.
Example: Set a timer for 1-minute intervals. At the beep, look up. Mark whether the student is on-task at that moment. Keep doing other work between beeps.
Use when: you need to take data while also working, or you're tracking more than one student.
Quick decision guide. I want to know whether the behavior held up the whole time: use whole-interval. I want to catch every time an unwanted behavior happens: use partial-interval. I need to take data while I'm also working with the student: use MTS. I'm tracking a group of students: use MTS (move through the group). I want the best estimate of how long: use MTS with short intervals.
Decide before you start: interval length, total watching time, and which method.
Common interval lengths:
10 seconds: high-rate behaviors. Needs your full attention.
30 seconds: a good mix of catching it and being doable.
1 minute: works for MTS when you have other jobs.
Use a timer to mark each interval. A phone, watch, or interval app works fine. Mark on a simple grid. Rows = intervals. Mark "+" or "-". Get the percent by dividing intervals with the behavior by the total intervals.
Report as percent of intervals. 14 of 20 intervals = 70%. Percent of intervals is not the same as percent of time. It's an estimate. The estimate depends on which method you used.
When you report to a supervisor or in a progress note, name the method. "70% of 30-second partial-interval intervals during independent math."
Try this. Match the method to the question. Whole-interval for behaviors you want to last. Partial-interval for behaviors you want to catch every time. MTS when you need to keep working. Write down which method you used. That way data can be compared across sessions.
Watch out for. Using one interval length, then switching without noting the change. Data from 10-second intervals can't really be compared to data from 1-minute intervals.
Bottom line. Interval recording is a flexible tool for behaviors that are hard to count. Pick the method that matches what you want to know. Be the same about it. Always name the method when you report the data.
Understanding whole-interval, partial-interval, and momentary time sampling: when to use each, how to take the data, and what the numbers actually mean.
Audience. Paras collecting behavioral or engagement data; supervising teachers training paras on observation methods.
Why Interval Recording?
Some behaviors are difficult to count in discrete units: a student's on-task engagement, self-stimulatory behavior that ebbs and flows, or sustained tantrums. Frequency counts don't capture these well. Interval recording offers a practical alternative: divide an observation period into equal time intervals, then mark whether the behavior occurred during, throughout, or at the moment of each interval.
All interval methods trade some accuracy for feasibility. None tells you exactly how much of the time a behavior occurred. They estimate it. Knowing which estimate you're making, and how to interpret it, is what makes the data useful.
Whole-Interval Recording
Mark the interval only if the behavior occurred for the ENTIRE interval.
Best for: behaviors you want to see sustained, on-task engagement, reading, remaining in seat.
Tendency: underestimates the true percentage of time the behavior occurs (because a single interruption causes you to miss the whole interval).
Example: 10-second intervals during independent work. Mark '+' only if the student was on-task for all 10 seconds. A student who drifts at second 9 gets a '-' for that interval.
Use when: you care about duration and sustained behavior, and you want a conservative estimate.
Partial-Interval Recording
Mark the interval if the behavior occurred at ANY point during the interval, even briefly.
Best for: behaviors you want to see reduced, disruptions, off-task behavior, stereotypy.
Tendency: overestimates the true percentage of time (a 1-second behavior in a 30-second interval still scores the whole interval).
Example: 30-second intervals during group instruction. Mark '+' if the student called out at any point during those 30 seconds.
Use when: you want a sensitive detector of behavior. You care whether it happened at all, not for how long.
Momentary Time Sampling (MTS)
Mark the interval based on what the student is doing at the exact moment the interval ends (or begins, pick one and be consistent).
Best for: frequent behaviors, group data collection, or situations where you cannot watch the student continuously.
Tendency: neither consistently over- nor under-estimates. It samples randomly across the observation, making it a reasonable approximation of true duration.
Example: Set a timer for 1-minute intervals. At the beep, look up and mark whether the student is on-task at that instant. Continue other work between beeps.
Use when: you need to collect data while also working, or you're tracking multiple students.
Choosing the Right Method
Setting Up Interval Recording
Decide before you start: interval length, total observation time, and which method. Common interval lengths:
10 seconds: High-frequency behaviors; requires full attention.
30 seconds: Good balance of sensitivity and feasibility.
1 minute: Practical for MTS when you have other responsibilities.
Use a timer (phone, watch, or an interval recording app) to signal each interval. Mark on a simple grid: rows = intervals, mark '+' or '-'. Calculate percentage by dividing intervals with the behavior by total intervals.
Interpreting Interval Data
Report as percentage of intervals: 14 of 20 intervals = 70%. Remember that percentage of intervals is not the same as percentage of time. It's an estimate that depends on which method you used. When reporting to a supervisor or in a progress note, name the method: '70% of 30-second partial-interval observations during independent math.'
| ✅ Try this | ⚠️ Watch out for |
|---|---|
| Match the method to the question: whole-interval for sustained behaviors, partial-interval for behaviors you want to catch every time, MTS when you need to keep working. Write down which method you used so data can be compared across sessions. | Using one interval length throughout a data collection period, then switching without noting the change. Interval data from 10-second intervals cannot be meaningfully compared to data from 1-minute intervals. |
Bottom line. Interval recording is a flexible tool for behaviors that are hard to count. The key is choosing the method that matches what you want to know, being consistent, and always noting the method when you report the data.
Reading is useful, but recall is where it sticks. Three short scenarios, low-stakes, no scoring. About 3 minutes. You can stop any time.
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