To randomize AB phase start single-case design teams define allowable intervention starts before outcomes, preserve minimum baseline and intervention lengths, then select one start by chance. Record the complete start window, probabilities, draw method, selected and delivered starts, statistic, and analysis. A randomized AB design still offers one phase change, so trend, history, replication, welfare, and limited power need explicit review.

Define the start window

Choose the earliest and latest intervention start that preserve adequate, ethical, and feasible phases. Give each allowable start a stable schedule ID.

Draw before outcome inspection

Use the declared random method before outcomes can guide the choice. Store the seed, random number, or physical draw evidence.

Preserve the selected and delivered starts

Record both fields even when they match. A delay, early start, or safety change becomes a visible deviation rather than a rewritten assignment.

Use the matching schedule set

The randomization analysis must compare the observed statistic with the same AB starts that could actually have been selected.

State the AB design limit

One transition offers one potential demonstration. Pair the result with raw trend, magnitude, context, and an honest plan for replication.

Build Nia's AB start-window register

For the randomize AB phase start single-case design question, start with a locked protocol and a versioned AB start-window register. Record Nia's design, setting, randomization unit, complete schedules, constraints, assignment probabilities, draw, selected schedule, delivered schedule, statistic, tail, tie and missing-data rules, software, and reviewers. Link each schedule position to the original time-series record. The file should let an independent analyst reconstruct randomized AB phase start without guessing what was possible before outcomes.

Work the schedule example for Nia

Nia's study has 14 observations and permits intervention to begin at observations 6, 7, 8, or 9. Those starts yield baseline lengths of 5 through 8 and intervention lengths of 9 through 6. Each receives probability 1/4. A documented draw selects observation 8 before baseline collection begins. Show the schedule generator, inclusion tests, probability calculation, draw evidence, and selected sequence at full precision. This fictional example illustrates a prospectively selected intervention start; it does not establish a universal phase length, alpha, power level, or treatment plan.

Audit Nia's assignment evidence

Nia's register lists the four schedules, equal probabilities, minimum phase rules, random-number output, selected start 8, actual delivery at 8, raw time series, and exact analysis scheme. All four starts remain in the reference set after the graph is visible. The audit also checks timestamps, protocol amendments, allocation concealment when applicable, cancellations, replacements, missing positions, phase labels, probability totals, software version, and whether the analysis generator matches the design generator. Unresolved discrepancies stay on hold.

Prevent the assignment error in Nia's review

Choosing the phase change in response to a favorable baseline pattern and later calling it randomized breaks the design claim. Nia's dated draw and locked start window separate prospective assignment from response-guided care. Randomization means chance operated at the named assignment step under the documented scheme. Varied, alternating, staggered, or response-guided schedules are not automatically randomized.

Integrate design and visual evidence for Nia

The report treats the AB result as one randomized phase comparison with limited replication. The team discusses possible trend, common history, delayed effects, and clinical importance and plans stronger replication when the question requires it. The WWC Version 5.0 handbook is a research-review standard, not a universal clinical protocol. Review the graph, level, trend, variability, immediacy, overlap, consistency, measurement quality, assignment fidelity, original-unit magnitude, and every planned replication.

Protect Nia's participation

The randomized AB phase start never outranks Nia's welfare. Keep augmentative and alternative communication, interpreters, mobility, food, water, bathroom use, prescribed care, health support, rest, relationships, and emergency help available. Use accessible consent and assent processes and honor withdrawal or distress. If safety, medical need, access, or choice changes the schedule, qualified people act and document the design consequence.

Use design-specific sources for Nia

For Nia's a prospectively selected intervention start, the BACB ethics hub and CASP public summary provide professional context, and the BCBA Test Content Outline identifies examination content on measurement and single-case design. A randomized SCED overview covers phase and alternation schemes. Research on multiple-baseline power, rapid alternation, and changing-criterion randomization shows design-specific behavior. A health-sciences methods paper discusses randomized phase, alternation, and case-placement options. Nonconcurrent multiple-baseline research addresses assignment and design-quality issues. ASHA supports continuous AAC access.

Rehearse Nia's schedule before collecting outcomes

Before the community cooking program begins, Nia's team runs the AB start-window register with fictional schedules and outcomes. The rehearsal checks the earliest and latest permissible assignment, probability totals, selected-schedule trace, delivered-schedule fields, statistic, missing-data behavior, and a hand-worked reference result. Reviewers store test cases, expected outputs, code version, and correction log. The dry run can repair mechanics before outcomes; it cannot use Nia's future data to change the assignment scheme.

Define Nia's stop, pause, and amendment rules

Nia's protocol names who may stop or pause the randomized AB phase start, which health, safety, assent, access, staffing, technology, or feasibility events trigger action, and how urgent care proceeds. It separates an immediate protective action from a later research amendment. Any amendment receives a new version, date, rationale, approval path, and prospective assignment set; the original schedule and data remain intact. The team also tells Nia how to withdraw or raise a concern through an accessible route. These rules make the humane response predictable and keep a necessary change from being hidden as ordinary schedule variation.

Close Nia's design review

Review the AB start-window register with Nia, the responsible clinician, and a statistician or methodologist familiar with the exact design. Preserve protocol, schedule set, probabilities, draw, selected and delivered sequence, raw data, graph, code, outputs, deviations, inference limits, client input, and decisions. Keep the page draft and noindex until every named review is complete.

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