Taking a closer look: time sampling and measurement error.
Interval time sampling badly over- or underestimates duration—switch to momentary time sampling when you need accurate duration data.
01Research in Context
What this study did
The team compared three ways to track how long a behavior lasts.
They used continuous recording as the gold standard.
They tested partial-interval, whole-interval, and momentary time sampling.
All sessions were videotaped so the true duration was known.
What they found
Partial- and whole-interval methods gave big, steady errors.
Momentary time sampling came much closer to the real duration.
The longer the interval, the worse the error for every method.
How this fits with other research
Neef et al. (1986) ran a near-copy study nine years later and still crowned momentary time sampling the winner for absolute duration.
Gardenier et al. (2004) repeated the test with preschoolers with autism and saw the same pattern: partial-interval recording blew stereotypy duration way up, while momentary time sampling stayed closer to the truth.
Sisson et al. (1993) warned that momentary time sampling can still lie if the behavior happens in many tiny bursts—so use it, but watch the bout pattern.
Boudreau et al. (2015) added that work-sampling equations demand far more samples than most BCBAs can take, so low-duration behaviors may still slip through the cracks.
Why it matters
If you need to know how long a client really stims, attends, or avoids work, drop partial- and whole-interval recording.
Switch to momentary time sampling with the shortest practical interval.
Check whether the behavior comes in quick bursts; if it does, sample more often or use continuous recording for key sessions.
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02At a glance
03Original abstract
A person manufactured his in-seat behavior for 15, 30-min sessions so that there were three blocks of five sessions where the behavior occurred 20%, 50%, and 80% of the time. Whole interval, partial interval, and momentary time-sample measures of the behavior were taken and compared to the continuous measure of the behavior i.e., per cent of time the behavior occurred. For interval time sampling, the difference between the continuous and sample measures i.e., measurement error, was: (1) extensive, (2) unidirectional, (3) a function of the time per response, and (4) inconsistent across changes in the continuous measure. A procedural analysis demonstrated that the frequency and duration of behavior are confounded in interval time sampling. Momentary time sampling was found to be superior to interval time sampling in estimating the duration a behavior occurs.
Journal of applied behavior analysis, 1977 · doi:10.1901/jaba.1977.10-325