Interval recording calculator (partial, whole interval and MTS)
Enter when the behavior started and stopped during an observation. The calculator scores it three ways (partial interval, whole interval and momentary time sampling) and compares each with the real share of time.
How each method scores an interval
- Partial interval: score the interval if the behavior happened at any point in it. Because a brief occurrence scores the whole interval, it tends to overestimate how much of the time the behavior happens. It suits behaviors you want to decrease.
- Whole interval: score the interval only if the behavior lasted the entire interval. It tends to underestimate, and suits behaviors you want to increase, such as staying on task.
- Momentary time sampling: score the interval if the behavior is happening at the moment the interval ends. It can over- or underestimate, and gets closer to the truth with shorter intervals.
All three are discontinuous: they sample the behavior rather than record every occurrence, and they report a percentage of intervals, not a count.
Try this
Change the interval from 30 seconds to 10 seconds. All three estimates move closer to the actual percentage: shorter intervals make discontinuous measures more accurate, at the cost of more recording.
Which method fits?
| Situation | Usual choice |
|---|---|
| A behavior to decrease that happens often and briefly, such as hand flapping | Partial interval: it overestimates, so it errs on the side of showing the problem. |
| A behavior to increase that should continue, such as engagement with a task | Whole interval: it underestimates, so progress isn't overstated. |
| One RBT observing several clients, or a long observation | Momentary time sampling: you only need to look at the end of each interval. |
| Every occurrence must be counted, such as aggression | None of these: use continuous measurement (frequency or rate). |
These are the usual reasons; your supervisor chooses the method for each target.
On the RBT exam
This calculator practises task A.2 Discontinuous measurement. On the exam you get a dry-erase board but no calculator, so once you've checked a few answers here, practise doing them by hand.