Minimizing and Reporting Momentary Time-Sampling Measurement Error in Single-Case Research

Cook et al. (2020) wrote a how-to guide for momentary time sampling (MTS).

They show where hidden error creeps in and give a quick fix: spot-check with real duration data.

The paper is for any single-case study that uses MTS to track behavior.

MTS can drift off by 20-a large share and you may never notice.

Adding a short duration-per-occasion probe every few sessions catches the drift.

If the probe and MTS line up, keep going; if not, retrain or switch methods.

Suhrheinrich et al. (2020) also trimmed fat: they swapped long trial-by-trial fidelity sheets for a 3-point Likert card and kept a large share agreement.

Both papers say busy staff can stay accurate with lighter tools—MTS plus quick probes or a slim checklist.

Jessel et al. (2020) warns that cutting an IISCA short weakens control; Cook’s probe rule keeps MTS brief but not blind, so brevity here does not trade away quality.

Iversen (2025) wants within-session replication; Cook’s spot-checks give the minute-level proof that control is holding across mini-cycles.

Next time you run MTS, set a phone alert. Every fifth session, flip to duration mode for ten minutes.

Log both numbers side-by-side. If they drift more than a large share, retrain your observer or adjust your sample window.

This five-minute habit saves your graph—and your credibility—with almost no extra work.