Interval Recording

Understanding whole-interval, partial-interval, and momentary time sampling — when to use each, how to take the data, and what the numbers actually mean.

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| Audience | Paras collecting behavioral or engagement data; supervising teachers training paras on observation methods. |

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| Why This Matters |

| Interval recording lets you measure behaviors that don't have a clear start and stop, or that happen too frequently to count individually. Understanding which method to use — and what each method actually measures — prevents the common error of collecting data that looks precise but answers the wrong question. |

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

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| Quick Decision Guide |

| I want to measure sustained behavior (how long something lasts): → Whole-interval |

| I want to catch every occurrence of an unwanted behavior: → Partial-interval |

| I need to collect data while I'm also working with the student: → Momentary time sampling |

| I'm tracking behavior across a group of students: → Momentary time sampling (cycle through the group) |

| I want the most accurate duration estimate: → Momentary time sampling (with short intervals) |

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.'

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| ✅ 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. | Use the same interval length throughout a data collection period, then switch without noting the change. Interval data from 10-second intervals cannot be meaningfully compared to data from 1-minute intervals. |

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| 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. |

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