Which time sampling method tends to underestimate the amount of behavior being measured?

• A. Whole Interval
• B. Momentary Time Sampling
• C. Partial Interval
• D. PLACHECK

Answer: (A)

The main idea to understand is how the timing of the observation affects what gets recorded. In whole interval recording, you only mark the target behavior as present if it occurs during the entire interval. If the behavior starts and stops within the interval or lasts only part of it, it won’t be counted. Because many brief or intermittent occurrences don’t span the whole interval, this method systematically underestimates how much behavior actually occurred when you look across many intervals or longer observation periods. For example, with short intervals, a student who engages in the behavior briefly several times will often not have any interval that contains the behavior for the full duration, so those bursts are missed.

Partial interval recording, by contrast, marks the behavior if it occurs at any moment within the interval, which tends to overestimate the total amount of behavior. Momentary time sampling checks at the end of the interval, so it may miss occurrences that happen earlier in the interval but not at the moment of check, and PLACHECK (group version of a momentary check) has a similar limitation in that it only captures a snapshot at the end of the interval.