A momentary time-sampling percentage equals valid checkpoints at which the defined response is occurring divided by all valid checkpoints, multiplied by 100. Define the exact observation instant and any grace rule. Report valid checkpoints divided by planned checkpoints separately. Keep missed prompts in a distinct missing state so they never become client nonoccurrence.

Define the checkpoint

Use a scheduled instant, response definition, visibility rule, and recording window.

Preserve missed prompts

Record workload, device, interruption, or other reason without filling a client score.

Calculate two percentages

Report positive divided by valid and valid divided by planned.

Bound the inference

Checkpoint occurrence is a sample and does not equal exact frequency or duration.

Choose checkpoints that represent the observation

Momentary time sampling scores the defined response at designated instants. The schedule should represent the activities, people, times, and settings tied to the decision. A convenient set of prompts concentrated in one part of a routine can produce a precise calculation that answers a narrow question.

Set the checkpoint spacing and observation window before collection. State whether the observer looks exactly at the signal or within a brief defined scoring window. Keep prompts predictable for the observer while considering whether audible or visible cues change the person's activity. When the cue could affect responding, use a discreet method and record the design.

Preserve every planned checkpoint

Build the sheet with one row per planned checkpoint. Mark present, absent, missed, invalid, or outside exposure. Record the reason for a missed point, such as blocked visibility or an observer responding to an urgent need. Do not silently convert missed checkpoints to absence.

Calculate response percentage from valid checkpoints and coverage from valid divided by planned checkpoints. If missed prompts cluster during a particular activity, time, or response pattern, the observed checkpoints may not represent the full period even when overall coverage looks acceptable.

Reproduce the calculation and interpretation

Count the planned checkpoints, then identify the valid denominator. Divide valid checkpoints scored present by all valid checkpoints and multiply by 100. Calculate coverage separately. Retain the counts, timing schedule, raw marks, rounding rule, and any software version used to produce the result.

Review the sampled percentage with a graph or table that shows observation dates and coverage. A change in checkpoint spacing, scoring window, routine, or observer creates a new measurement condition. Mark that change visibly before comparing results across phases.

Build the calculation around a clear decision

The momentary time-sampling worksheet for Hana identifies the response definition, unit, interval or event boundary, planned exposure, valid denominator, missing-state rule, calculation, responsible qualified role, and review date before data collection.

Worked example: scheduled checkpoints

Hana has 30 planned checkpoints. Three prompts are missed, leaving 27 valid checks; the response is present at nine. Momentary time-sampling percentage is 9 divided by 27, or 33.3%. Coverage is 27 divided by 30, or 90%.

Report coverage with the result

For Hana, report planned, observed, valid, positive, negative, missed, invalid, and outside-exposure units as applicable. Preserve raw records, timestamps, interval length, procedure version, and rounding. A sampled percentage retains the limits of the selected procedure.

Keep access available during measurement

During the reproducible checkpoint sampling review for Hana, keep AAC, interpreters, mobility, food, water, bathroom use, prescribed care, health support, rest, relationships, and emergency help available. Record access or health changes and use accessible communication to ask whether the outcome matters.

Use evidence within its stated scope

For Hana, the BACB ethics hub and CASP public summary provide professional context. The BCBA Test Content Outline covers continuous and discontinuous procedures, temporal dimensions, product measures, validity, reliability, and representative measurement as examination content.

For the reproducible checkpoint sampling question, Pritchard and colleagues and Wirth and colleagues examine accuracy and decision implications of discontinuous measurement procedures. Lobo and colleagues supply single-case measurement and analysis context. ASHA says AAC users should always have access to their communication tools or devices. These sources support careful method selection without creating a universal interval length, correction factor, or clinical threshold.

Document the clinical review

Review the momentary time-sampling worksheet with Hana and the responsible clinician. Record the procedure, raw data, coverage, calculation, limitations, selected action, owner, next sample, and review date. Reopen the method when the response pattern, access, setting, interval, exposure, system, or decision changes.

Clinician review checklist

  • Do planned checkpoints represent the decision-relevant parts of the routine?
  • Is the scoring instant or scoring window defined precisely?
  • Are present, absent, missed, invalid, and outside-exposure states distinct?
  • Are response percentage and checkpoint coverage reported separately?
  • Did missed prompts cluster in a way that could affect interpretation?
  • Are schedule and procedure changes marked before comparisons are made?
  • Can the client review the outcome through an accessible communication method?

Related resources

Sources