2.3 Discontinuous Measurement: Interval Recording and MTS

Discontinuous Measurement: Interval Recording and MTS

Discontinuous measurement records samples of behavior during an observation period rather than every response. The 2026 RBT Test Content Outline includes partial interval recording, whole interval recording, and momentary time sampling. These procedures are useful when continuous measurement would interfere with instruction or when the target is difficult to count continuously. They are also easy to misuse. The RBT must understand what each method records and what it tends to exaggerate or miss.

In interval recording, the observation period is divided into equal intervals, such as 10 seconds, 30 seconds, or 1 minute. The RBT marks each interval according to the rule in the plan. For partial interval recording, the interval is scored if the behavior happens at any time during the interval, even for one brief moment. If the interval is 30 seconds and the client taps the table once, the RBT marks occurrence for that interval. This can be useful for behavior reduction targets when the team wants to know whether behavior appeared during portions of the session.

Because one brief response scores the same as behavior lasting the entire interval, partial interval recording may overestimate total behavior.

Whole interval recording uses a stricter rule. The RBT scores the interval only if the behavior occurs throughout the entire interval. If engagement is defined as looking at materials, manipulating task items, or writing as assigned, and the client is engaged for 27 of 30 seconds, that interval is not scored as occurrence under whole interval recording if the plan requires the full interval. Whole interval recording is often used when the team wants to increase continuous behavior, such as sustained engagement or staying in an area.

Because a brief interruption makes the interval nonoccurrence, whole interval recording may underestimate behavior.

Momentary time sampling, or MTS, records whether the behavior is occurring at a specific instant, usually when the interval ends. If the RBT uses 1-minute MTS for on-task behavior, they look at the client at the end of each minute and mark whether the client is on task at that exact moment. What happened during the rest of the minute is not scored. MTS can be practical in classrooms because the RBT can observe briefly at scheduled moments while still supporting instruction. The tradeoff is that behavior occurring between checks may be missed.

Discontinuous Measurement Comparison Table

A practical example shows the difference. During a 5-minute observation divided into ten 30-second intervals, a client engages in hand mouthing for two seconds near the beginning of each interval. Partial interval recording would show occurrence in all ten intervals, or 100% of intervals. Whole interval recording would show 0% because the behavior did not last through any full interval. MTS might show 0%, 100%, or something between, depending on whether hand mouthing happened at the exact observation moments. None of these results is wrong if the method was implemented correctly.

They answer different measurement questions.

The RBT's job is to preserve the rule, not to adjust it based on intuition. If the written plan says partial interval, the RBT should not decide to mark only intervals where behavior lasted most of the time. If the plan says MTS, the RBT should not mark behavior that happened 10 seconds before the timer sounded unless the behavior is still occurring at the sample moment. Small changes like these can make graphs look better or worse without any true behavior change.

Timing discipline is essential. The RBT should know the interval length, how cues will signal interval endings, where data will be recorded, and how to handle moments when safety or instruction prevents immediate marking. Some teams use interval apps, vibrating timers, or paper grids. The RBT should follow workplace rules for device use and confidentiality. If a timer fails or the RBT misses several intervals, the data sheet should not be quietly filled in from memory. The RBT should document the interruption and tell the supervisor according to the reporting procedure.

Discontinuous data are often summarized as percentage of intervals with occurrence. This percentage is not the same as percentage of time, especially for partial and whole interval systems. Saying aggression occurred during 40% of intervals is more accurate than saying the client was aggressive 40% of the session, unless the measurement system truly supports that statement. This distinction matters in notes, caregiver communication, and supervisor updates. RBTs should use the language of the measurement system and avoid overstating what sampled data show.

Good discontinuous measurement balances practicality and honesty. It lets the RBT collect consistent data in busy sessions, but it requires respect for the limitations of sampling. When candidates understand the bias of each method, they are better prepared to choose the option that matches a scenario in training and to implement assigned procedures faithfully in practice.