Zero PND with level change can occur when one baseline extreme sets a reference that every intervention point overlaps, even though most baseline values and the intervention level differ. Preserve and investigate the extreme rather than deleting it automatically. Report PND with the raw graph, median, distribution, measurement conditions, and other planned analyses so one reference point does not control the whole conclusion.

Identify the controlling extreme

Show the baseline value that sets the PND reference and which intervention points fail to exceed it. Keep dates and conditions visible.

Validate the source value

Check definition, unit, observer, device, timestamp, context, and correction history. Resolve errors through the documented data-correction process.

Describe both distributions

Report medians, ranges, raw points, and phase sizes. Avoid relying on a mean that may also be dominated by the extreme.

Use complementary planned views

Pair PND with the raw graph and any preselected median, pairwise, or distance analysis. Label differences as metric sensitivity.

Explain the zero precisely

State that no intervention point exceeded the valid baseline extreme. Do not translate 0% PND into no change, no value, or treatment failure.

Build Ximena's baseline-extreme diagnostic table

Start with a locked worklist for Ximena. Record the review question, metric name, formula version, phase labels, improvement direction, planned and valid observations, missing or invalid states, tie handling, trend handling, source timestamps, calculation owner, and review date. The zero-PND outlier review result should be reproducible from this worklist without relying on an unlabeled dashboard value. Keep the data in their original unit so reviewers can connect the supplement to the graph and to the actual outcome. For the zero PND with level change question, Ximena's reviewer also records the release criterion, expected evidence, unresolved limitations, and exact action that the result may inform. This small decision log prevents a calculation from becoming an open-ended label and lets a later reviewer distinguish the observed value from the judgment made with it.

Work the calculation for Ximena

Ximena's baseline values are 10, 12, and 100; intervention values are 20, 22, 24, and 26; higher is preferred. The baseline maximum is 100, so PND is 0 of 4, or 0%. The baseline median is 12, and all four intervention values exceed it, so strict PEM is 4 of 4, or 100%. Show every intermediate count or statistic at enough precision to reproduce the displayed result. Keep the raw phase values in chronological order beside any sorted, paired, or transformed table. The fictional arithmetic illustrates the method; it does not create a clinical threshold, minimum phase size, or promised treatment effect.

Audit Ximena's denominator and formula

Ximena's diagnostic table traces the value 100 to its date, observer, context, and source record. It confirms that 100 is valid before retaining it. It reports the baseline range 10 to 100, intervention range 20 to 26, and both PND and PEM without choosing one as automatically correct. The audit also checks duplicate timestamps, silent imputation, phase-boundary drift, direction reversal, premature rounding, spreadsheet ranges, software version, and correction history. Any unresolved source discrepancy stays on hold with an owner and due date instead of being converted into a convenient zero or exclusion.

Watch for the main failure mode in Ximena's review

Deleting the outlier solely because it lowers PND biases the analysis. Keeping it without investigating a device error or definition change is also unsafe. Ximena's gate separates source validation from metric interpretation. Reviewers should be able to see how one point, tie, extreme, missing observation, or phase-length decision affects the result. A sensitivity example is labeled as hypothetical and never mixed with observed evidence.

Integrate the metric with visual and design analysis for Ximena

After validating 100, the qualified reviewer examines whether it reflects genuine variability, a different condition, or a measurement problem. The report integrates typical level, trend, overlap, pairwise ordering, distance, and phase replications, then states why PND is insensitive to the observed pattern. The WWC Version 5.0 handbook is a research evidence standard, so its design criteria are not a universal clinical protocol. In care, the responsible clinician also considers current assessment evidence, professional scope, the treatment plan, ordinary supports, risk, and the person's choices.

Protect client relevance and access for Ximena

During Ximena's a PND result dominated by one baseline outlier review, keep augmentative and alternative communication, interpreters, mobility, food, water, bathroom use, prescribed care, health support, rest, relationships, and emergency help available. Use accessible communication to ask whether the goal, direction, magnitude, burden, and observed change matter to Ximena. A favorable coefficient cannot repair an unwanted target, inaccessible measurement process, unsafe plan, or missing consent and assent process.

Use current evidence within scope for Ximena

For Ximena's zero-PND outlier review review, the BACB ethics hub and CASP public summary provide professional context, while the BCBA Test Content Outline supplies examination scope for measurement, graphing, interpretation, experimental design, and data-based evaluation. A single-case methods review describes common overlap, Tau, and two-SD calculations. Decision-accuracy research shows why phase size and design structure matter and why overlap percentages do not measure distance. A reproducibility tutorial documents ambiguity among Tau-U implementations and baseline corrections. Nonoverlap and mean-difference methods explain their distinct information targets. ASHA supports continuous access to AAC tools or devices.

Close Ximena's supplemental analysis review

Review the baseline-extreme diagnostic table with Ximena and the responsible qualified clinician. Preserve source data, graph, phase definitions, calculation specification, coverage, ties, uncertainty, limitations, client input, selected action, owner, and next review date. Reopen the analysis when the measure, phase, context, access, health, goal, software, or design changes. The final note should make clear which conclusions are supported, which remain uncertain, and which require different evidence.

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