The Effect of Phototherapy on Pruritus of Patients With Chronic Kidney Disease: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The Effect of Phototherapy on Pruritus of Patients With Chronic Kidney Disease (NCT00494975), a randomized na study. The primary outcome is Visual Analogue Scale (VAS) Score for Pruritus.

2. Clinical Question

The clinical question concerns symptom intensity, measured using a visual analogue scale (VAS). The trial description says the VAS is a horizontal line 100 mm in length, with 0 corresponding to no pruritus and 10 to the most severe pruritus. Patients mark the point that represents their perception of pruritus. The primary outcome is listed as the mean VAS score at baseline and after 6 -week phototherapy.

The study description also says investigators assessed pruritic intensity at baseline and every 3 sessions, and used a detailed questionnaire at baseline and after 18 sessions. A separate secondary outcome is listed as the detailed questionnaire at baseline and after 18 sessions. The registry record does not provide a detailed account of the questionnaire results.

The reported arm-level values are negative in both groups, consistent with decreases in the recorded score if the values represent change as described in the posted results. The registry also reports a GEE comparison of final values. That comparison is distinct from a direct comparison of the arm-level change values, so the two should not be treated as interchangeable summaries.

3. Trial Design

The registry describes a randomized, single-masked, parallel-group study. Participants were assigned to ultraviolet A phototherapy or narrow band ultraviolet B phototherapy. The record lists 21 participants enrolled and identifies National Taiwan University Hospital as the sponsor. The trial status is completed, and the listed phase is NA.

The registry lists a start date of 2007-06 and a primary completion date of 2009-07. The primary outcome was a continuous measure: the mean VAS score for pruritus, with standard deviation as the dispersion measure. The stated timeframe is VAS score at baseline and after 6 -week phototherapy. The study description also refers to assessments at baseline and every 3 sessions, and to a detailed questionnaire at baseline and after 18 sessions.

The outcome results list 8 participants for ultraviolet A and 10 for narrow band ultraviolet B. The safety information uses different at-risk counts: 10 for ultraviolet A and 11 for narrow band ultraviolet B. The record does not explain why these sets of counts differ, or how the listed enrollment relates to each analysis denominator. They should therefore be read as the denominators reported for their respective results, not combined into a single analysis population.

The masking field says single, but the record does not identify which people were masked or describe how masking was maintained. The allocation field says randomized; details of sequence generation, allocation concealment, or assignment procedures are not reported in the registry record. The record also does not report a sample-size justification, the intended analysis populations, or a more detailed statistical analysis plan. These omissions limit how fully the design and conduct can be assessed from the registry entry alone.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Visual Analogue Scale (VAS) Score for Pruritus, measured over VAS score at baseline and after 6 -week phototherapy.

The primary endpoint is the visual analogue scale (VAS) score for pruritus, summarized as a mean with standard deviation. The record describes the VAS as a horizontal line 100 mm in length on which a patient marks the point that best represents their perception of pruritus. Its stated anchors are 0 for no pruritus and 10 for the most severe pruritus. The score is therefore intended to represent a patient-reported measure of symptom intensity.

The registry identifies the timeframe as VAS score at baseline and after 6 -week phototherapy. It also says the investigator assessed pruritic intensity at baseline and every 3 sessions. These repeated assessments can describe how scores changed over time, but the record does not give a complete schedule of all visits or explain which observations entered the reported analysis.

Using a continuous score preserves gradations in symptom ratings rather than reducing them to categories. General statistical context: a mean describes the average score in a group, while a standard deviation describes how spread out individual scores are around that average. Neither summary alone shows every participant’s experience, and the registry does not report the underlying individual scores.

The arm-level results list values of -3.38 for ultraviolet A and -3.53 for narrow band ultraviolet B, each with a standard deviation. The record does not explicitly define the sign convention for these values in the results field, although the outcome description refers to assessments over time. The separate reported GEE analysis compares final values, so it should not be assumed to be a comparison of those two listed arm-level values.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry reports a generalized estimating equations (GEE) method for comparing final VAS values between the ultraviolet A and narrow band ultraviolet B groups. It labels the reported parameter as a mean difference in final values and gives a 95% confidence interval and a p-value. The entry does not provide the full model specification, so the result can be described as reported without assuming details that are not documented.

What does GEE do?

General statistical context: GEE is a method commonly used when observations are correlated, such as repeated measurements from the same participant. Measurements from one person are generally not treated as independent of each other, because they come from the same individual. GEE accounts for this within-person correlation when estimating a population-average association or difference. The method is not a description of the study design itself, and its use does not reveal which measurement times were included.

The study description refers to VAS assessments at baseline and every 3 sessions. That makes repeated measurements relevant to understanding the stated method. However, the registry does not report exactly which visits were included in the GEE analysis, whether baseline was part of the modeled outcome, how the visits were represented, or what working correlation structure was used. It also does not list adjustment variables. These omissions mean that a reader cannot reconstruct the analysis from the registry entry.

How should the interval and p-value be read?

The reported mean difference in final values is 0.94, with a 95% confidence interval from 0.31 to 1.56, and p <0.05. General statistical context: a confidence interval describes uncertainty around an estimate under the model and its assumptions. A narrower interval indicates greater precision than a wider interval would, while an interval that includes zero is compatible with no difference under the usual interpretation of a mean difference. Here, the posted interval does not include zero. The p-value reports how unusual data at least as incompatible with a specified null model would be if that null model and the analysis assumptions held. It does not give the probability that the null hypothesis is true, nor does it measure clinical importance.

The registry lists the comparison groups as ultraviolet A and narrow band ultraviolet B but does not state the subtraction order for the mean difference. Therefore, the positive estimate cannot be assigned a direction in terms of which group had the higher final score solely from the entry. The confidence interval and p-value should likewise be understood as properties of the reported contrast, without adding an unstated direction.

What do the arm summaries add?

The arm-level outcome values are -3.38 with standard deviation 2.59 for ultraviolet A and -3.53 with standard deviation 3.49 for narrow band ultraviolet B. The corresponding listed participant counts are 8 and 10. The standard deviation describes variability among individual values around the arm mean; it is not the uncertainty interval for the mean difference. An arm-level mean and standard deviation do not by themselves supply a complete adjusted or repeated-measures comparison. In particular, the registry does not report baseline arm summaries, so a reader cannot use these results to reconstruct changes from baseline or the GEE model.

The record states that values are missing or not estimable for a two-arm comparison of this continuous endpoint. Consequently, there is no posted recalculated comparison to use as an independent check on the GEE result. General statistical context: unadjusted calculations from summary statistics can differ from a model-based analysis because they may address a different estimand and may not account for repeated observations or covariates. When a registry identifies a discrepancy between a sponsor analysis and a recalculation, the sponsor’s own analysis takes precedence; no such discrepancy is flagged in this record.

What does the sample-size illustration mean?

The registry’s sample-size assumptions describe planning illustrations based on the observed effect, with two-sided significance level 0.05, equal allocation between groups, and a normal approximation. The effect to detect is defined as a stated fraction of the observed effect. Such illustrations are hypothetical planning calculations, not the trial’s original design justification and not observed power. The record does not report the trial’s own sample-size justification or whether the planning assumptions match its design.

General statistical context: power is a design quantity based on assumptions about a target effect, variability, significance level, and allocation. It is not a retrospective measure of whether a completed study has established a result. A small study can yield an imprecise estimate, while a statistically notable result can still have uncertainty about its size and meaning. The registry provides no basis to infer the original planned enrollment or the rationale for the number enrolled.

What cannot be established from the method entry?

The registry does not report the GEE working correlation structure, model diagnostics, treatment of missing measurements, or exact analysis population. It does not say whether the analysis followed the randomized assignments or included only participants with particular measurements. It also does not report interim analyses, a broader statistical analysis plan, or multiplicity adjustments. These points are not evidence that any particular procedure was or was not used; they are details not reported in the registry record. Interpretation should remain tied to the reported method and its stated limits.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Ultraviolet A Phototherapy", "Narrow Band Ultraviolet B Phototherapy")
n   <- c(8, 10)
m   <- c(-3.38, -3.53)
sp  <- c(2.59, 3.49)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Ultraviolet A Phototherapy  8  -3.380  2.590  -5.545  -1.215
CARM  Narrow Band Ultraviolet B Phototherapy  10  -3.530  3.490  -6.027  -1.033

11. Analyses Reported by the Sponsor

The registry’s reported analysis is a GEE comparison of final VAS values, with a mean difference of 0.94, a 95% confidence interval from 0.31 to 1.56, and p <0.05. The arm-level values and standard deviations are also reported, but the record indicates that values needed for a recalculated two-arm comparison of this continuous endpoint are missing or not estimable. There is therefore no numerical recalculation to compare directly with the reported GEE estimate.

The registry does not flag a discrepancy between the reported analysis and a recalculation. The GEE result should consequently be described as the registry’s posted analysis, without presenting a separate estimate as if it were a replication or correction. The record does not report enough model detail to reconstruct the analysis from the arm summaries, and the group order alone does not establish the subtraction order for the reported mean difference.

More broadly, a recalculation from summary statistics would be an unadjusted calculation and could answer a different question from a repeated-measures GEE model. General statistical context: model-based and unadjusted estimates can differ because they use different information or assumptions. In this record, the sponsor-reported result is the only posted comparative estimate for the primary continuous outcome, while its full model specification is not reported in the registry record.

12. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome, the VAS score for pruritus, and one secondary outcome, a detailed questionnaire at baseline and after 18 sessions. The record reports two outcome measures and one analysis. It does not provide detailed results for the secondary questionnaire in the listed outcome information. The details of any additional analyses are not reported in the registry record.

Multiplicity arises when many outcomes, time points, or statistical comparisons are tested. General statistical context: as the number of tests increases, the chance of obtaining at least one apparently notable result by chance can increase unless the analysis plan accounts for that multiplicity. The registry does not report whether the investigators adjusted for multiple testing, designated a hierarchy of outcomes, or specified a testing strategy. It would therefore be inappropriate to assume that multiplicity was addressed or ignored.

The record does not describe missing outcome data, participant withdrawals, or the number of participants with a VAS measurement at each assessment. It also does not state how missing observations were handled in the GEE analysis. Although the reported outcome counts are 8 and 10, the safety information lists at-risk counts of 10 and 11. The reason for the difference is not reported in the registry record, and the analysis populations cannot be inferred from these counts alone.

The registry does not state whether analyses followed the randomized assignment, used a per-protocol population, or included another defined set of participants. It also does not report an intention-to-treat definition, exclusions from analysis, or sensitivity analyses. These omissions limit assessment of the potential effect of missing data and analysis-population choices. General statistical context: missingness can affect interpretation when the likelihood of having an observed outcome is related to the outcome itself or to participant characteristics. Without details about missingness and handling, its impact cannot be quantified from the posted record.

There is also no reported protocol or complete statistical analysis plan in the registry entry that would allow readers to assess whether all planned outcomes and analyses were reported. This is a limitation of the information recorded, not evidence that outcomes or analyses were selectively omitted. The available entry supports interpretation of the listed primary comparison, with explicit caution about unreported multiplicity, missing-data procedures, and analysis populations.

13. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 5% reporting threshold.

The registry lists zero serious adverse events among 10 participants at risk in the ultraviolet A group and zero among 11 participants at risk in the narrow band ultraviolet B group. These safety denominators differ from the primary outcome participant counts, which are 8 and 10. The record does not explain the difference, so the safety figures should be read using their own stated denominators rather than substituted for the efficacy counts.

The registry also lists zero other adverse events in each safety group. The deaths fields are null, and the record does not identify any serious adverse-event terms. Null death entries are not the same as a reported numerical count of zero; whether deaths were assessed or not reported in a particular way is not explained. The reasons for the differing safety denominators are also not reported in the registry record.

General statistical context: zero recorded serious events in a small group does not establish that the underlying risk is absent. It means that no serious events are recorded for the listed at-risk participants during the registry’s reporting period. The record does not provide the duration of safety follow-up, event definitions, collection procedures, or detailed exposure information. Those omissions limit comparisons between groups and interpretation of the safety profile. These figures describe the posted safety counts and should not be treated as evidence about events beyond those recorded.

14. What the Result Does, and Does Not, Mean

The registry reports arm-level VAS values of -3.38 for ultraviolet A and -3.53 for narrow band ultraviolet B, and a GEE comparison of final values with an estimate of 0.94. The reported 95% confidence interval is 0.31 to 1.56, with p <0.05. Together, these figures describe the available results for the recorded pruritus outcome. They do not by themselves establish whether the difference is important to patients, because the registry does not report a threshold for clinical importance.

The result does not establish which group had the higher final score: the record lists the groups but does not state the subtraction order for the mean difference. Nor should the GEE estimate be interpreted as a direct comparison of the arm-level change values. The analysis is described as a final-value comparison, while the arm-level result and endpoint description concern scores over time. Baseline summaries and detailed model specifications are not reported, preventing a fuller reconstruction of the contrast.

General statistical context: a statistically notable result is not the same as a precise or clinically important result. The confidence interval describes uncertainty under the analysis assumptions, and the p-value addresses compatibility with a null model. Neither gives a direct probability that a treatment is effective or ineffective. The record does not report how patients valued the observed score differences or how the VAS relates to other outcomes.

The study was randomized and parallel-group, but the registry entry does not describe allocation procedures, who was masked, the analysis populations, or missing-data handling. The primary outcome counts are smaller than the stated enrollment, and the safety denominators differ from the outcome counts. The reasons are not reported. These limits mean the posted result should be read as a result for the participants and analysis represented by the registry entry, not assumed to describe every enrolled participant.

The record does not support medical advice or a conclusion about treatment choice. It supports a statistical description of the reported symptom scores and model-based comparison, subject to uncertainty and reporting gaps. Further details would be needed to determine the direction and clinical relevance of the reported contrast, assess sensitivity to missing data, or evaluate whether the findings generalize beyond the listed study population.

15. Why This Trial Matters Statistically

This trial illustrates why a clinical outcome and its statistical contrast need to be read separately. The primary endpoint is a patient-reported VAS score for pruritus, while the reported comparative analysis is labeled as a GEE mean difference in final values. The arm-level values are also listed as continuous summaries. Without the baseline results and full model specification, these summaries cannot be treated as interchangeable estimates of the same quantity.

The example also shows how reporting denominators shape interpretation. The record lists 21 participants enrolled, primary outcome counts of 8 and 10, and safety counts of 10 and 11. Those figures do not align, and the registry does not explain why. A careful statistical reading preserves each denominator as reported instead of assuming that one represents the complete analysis population or reconciling them without evidence.

The GEE label signals that the analysis may address correlated observations, which is relevant because the study description mentions repeated VAS assessments. But a method name alone does not provide a reproducible analysis. The working correlation structure, included time points, missing-data handling, and analysis population are not reported. The interval and p-value are useful summaries of the posted comparison, but they cannot answer those design and reporting questions.

The record is also a reminder that statistical evidence and clinical importance are distinct. The reported confidence interval does not include zero, and the registry reports p <0.05, but no clinical-importance threshold is listed. The sign of the difference is not interpretable without a stated subtraction order. Readers can identify what was reported while remaining cautious about what cannot be determined.

These features matter in biostatistical practice because reliable interpretation depends on the estimand, outcome definition, analysis population, and uncertainty—not on a single p-value. This trial’s registry entry supports a focused account of the VAS results while also showing why incomplete model and population details constrain conclusions.

16. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The registry entry leaves several trial-specific details unresolved. Although it identifies the study as randomized and single-masked, it does not describe sequence generation, allocation concealment, or who was masked. It lists 21 participants enrolled but gives primary outcome counts of 8 and 10 and safety denominators of 10 and 11. No explanation for these differing numbers is reported. The record therefore does not permit a clear account of participant flow or the analysis population.

The VAS timeframe is stated as baseline and after 6 -week phototherapy, while the study description refers to assessment at baseline and every 3 sessions and a questionnaire after 18 sessions. The registry does not provide a complete visit schedule or specify which measurements informed the GEE comparison. It also does not give baseline arm-level scores, which limits interpretation of change and prevents reconstruction of a baseline-adjusted or repeated-measures contrast.

The reported GEE analysis lacks model details, including the working correlation structure, included covariates, and treatment of missing observations. The registry does not report missing-data patterns, exclusions, analysis-set definitions, interim analyses, or a complete statistical analysis plan. It also does not report a sample-size justification. The sample-size assumptions are described as planning illustrations based on the observed effect, not as the trial’s original design rationale.

The reported mean difference has no stated subtraction order. This prevents confident assignment of its positive direction to one group. The record also provides no clinical-importance threshold for interpreting the VAS contrast, and detailed secondary questionnaire results are not listed. Multiplicity procedures are not reported. These are reporting limitations; they do not establish which methods were used or whether any particular problem occurred.

Finally, the safety record reports zero serious events in the stated risk groups but does not provide the safety follow-up duration or event-collection details. Death entries are null rather than numerical zero counts. This limits interpretation of the safety information and comparison of the safety denominators with the primary outcome counts.

17. Related Tutorials

18. Related Statistical Calculators

19. Sources

• ClinicalTrials.gov: The Effect of Phototherapy on Pruritus of Patients With Chronic Kidney Disease — NCT00494975.
• Registry record last updated 2011-01-27; status last verified 2010-09.
• Results first posted 2011-01-25.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

20. Record Summary

NCT00494975 is a completed randomized, single-masked, parallel-group study of ultraviolet A phototherapy and narrow band ultraviolet B phototherapy for uremic pruritus in patients with chronic kidney disease. National Taiwan University Hospital is listed as sponsor. The record lists 21 participants enrolled, a start date of 2007-06, and a primary completion date of 2009-07.

The primary outcome was mean VAS score for pruritus, with standard deviation. The posted arm-level values are -3.38 for ultraviolet A and -3.53 for narrow band ultraviolet B. The reported GEE comparison of final values is 0.94, with a 95% confidence interval of 0.31 to 1.56 and p <0.05. The subtraction order is not stated.

Primary outcome counts are 8 and 10; safety denominators are 10 and 11. The record does not explain the differences or report detailed analysis populations, missing-data procedures, or a full GEE specification. It lists zero serious adverse events in each safety group, while death entries are null.