Use of Cidofovir for Recurrent Respiratory Papillomatosis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Use of Cidofovir for Recurrent Respiratory Papillomatosis (NCT00205374), a randomized phase 4 study. The primary outcome is Change in Papilloma Severity.

2. Clinical Question

Statistically, this is a question about between-group differences in change, rather than whether either group changed in isolation. A change within the cidofovir group alone would not establish that its course differed from placebo. The registry record does not give estimates, uncertainty intervals, or tests for the primary or secondary outcomes, so the treatment comparison cannot be quantified from the reported information.

3. Trial Design

The registry identifies NCT00205374 as a completed phase 4 study sponsored by the University of Wisconsin, Madison. The trial began in 1999-11, and primary completion is recorded as 2009-12. It enrolled 19 participants. The design is classified as randomized, double-masked, and parallel-group, with cidofovir and placebo as the interventions.

Randomization is intended to assign participants to treatment groups by chance, rather than by clinical judgment. In general, this can reduce systematic differences between groups at the start of a trial, although chance imbalances can remain, particularly in a small study. The registry says a restricted randomization procedure in groups of 4 was intended to encourage uniformity in sample sizes. It does not report the sequence-generation method, allocation concealment procedures, or the actual number randomized to each group in the trial-design information.

Parallel-group means that participants are assigned to a group and assessed under that assigned intervention, rather than crossing between interventions as part of the stated design. Double-masked indicates that the registry classifies the study as masked, but the record does not identify exactly who was masked or describe how masking was maintained. The posted information also does not report treatment adherence, withdrawals, or the number assessed at each follow-up.

The registry lists baseline, 2 months, and 12 months as assessment times for the primary endpoint, and describes change in Voice Handicap Index score at 12 months as a secondary outcome. Its primary-outcome description refers to both papilloma severity and inter-surgery intervals when stating the efficacy criterion. Those details indicate the intended clinical comparison, but they do not substitute for outcome results or a statistical analysis plan. The plan for handling repeated assessments, missing observations, or departures from assigned treatment is not reported in the registry record.

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.

Before assignment: Before inclusion in this study, and 48 hours before each cidofovir injection, laboratory tests confirmed that the (female) participants were not pregnant and that laboratory findings were not exclusionary for study participation.

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 Change in Papilloma Severity, measured over Baseline, 2 months, and 12 months.

The primary endpoint is titled “Change in Papilloma Severity.” It uses the Derkay Severity Score, a score for which the registry states a minimum of zero and a maximum of 86. Higher ratings indicate more advanced disease and a worse outcome. Assessments are specified at baseline, 2 months, and 12 months. The primary outcome population field is blank.

The registry description explains that the score incorporates features such as voice, stridor, urgency of intervention, respiratory distress, and lesions at anatomical sites in the upper airway. At multiple anatomical sites—18 or more, as described in the record—lesions are rated according to their appearance. The combination is intended to represent severity across more than a single symptom or lesion location. This can be useful when a condition varies in presentation, but a composite score may also make it harder to tell which component accounts for a change.

Change from baseline is used to describe whether severity scores move over time. A comparison between groups is needed to assess whether the observed changes differ between cidofovir and placebo. The registry record does not report the group scores, changes, or their uncertainty, and therefore does not establish the direction or size of any difference.

The efficacy description additionally refers to inter-surgery time intervals, but the listed primary endpoint is the change in severity score. The registry record does not report an interval estimate or comparative result for surgery timing. The secondary endpoint is change in Voice Handicap Index score at 12 months; its results are also not reported.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry classifies the study as randomized, double-masked, and parallel-group. Those labels describe broad design features, but they do not provide a full statistical methods account. The record does not report the analysis model, the primary contrast’s exact definition, or the method used to address repeated outcome assessments. The explanations below describe general statistical concepts and distinguish them from methods that can be confirmed for this trial.

What does randomization contribute?

In general, random assignment aims to make treatment groups comparable in expectation with respect to measured and unmeasured characteristics at the start of a trial. It does not guarantee identical groups in a particular study. This is especially relevant when enrollment is limited, because chance differences in prognostic characteristics can have an appreciable influence on estimates. The registry says a restricted randomization procedure in groups of 4 was intended to encourage uniformity in sample sizes. It does not report the actual allocation sequence, allocation concealment, or the final treatment-group sizes in the design information.

Randomization also does not, by itself, specify how the outcome analysis should be conducted. An analysis may compare follow-up scores, changes from baseline, or trajectories over time. These choices target related but not necessarily identical quantities. The registry lists change in severity as the primary outcome and gives the assessment schedule, but the actual analysis approach is not reported in the registry record.

How should repeated measurements be understood?

Severity is to be assessed at baseline, 2 months, and 12 months. These measurements from the same participant are related, so they should not generally be treated as if they came from unrelated people. In general, a repeated-measures approach can account for within-person correlation and use the available follow-up pattern under assumptions about the data. A simpler analysis might instead compare changes at a specified follow-up. The appropriate choice depends on the intended estimand, missingness, and prespecified analysis plan. The registry record does not state which approach was used, whether a particular follow-up was the primary contrast, or how correlation between measurements was handled.

The outcome description also refers to inter-surgery time intervals. Analyses of elapsed time can require methods that account for unequal observation periods and censoring, when these occur. That is a general consideration, not a description of an analysis confirmed for this trial. The registry record does not report a time-to-event method, an interval estimate, or an analysis of surgery timing.

What does the severity score represent?

The Derkay Severity Score combines ratings involving voice, stridor, urgency of intervention, respiratory distress, and lesions at anatomical sites. The stated score range runs from a minimum of zero to a maximum of 86, and higher values represent more advanced disease and a worse outcome. In general, a composite score can condense several clinical features into a single measure, making it possible to summarize overall severity. It can also conceal differences among components: a similar total score can arise from different patterns of symptoms or lesions. The registry record does not report component-level results or explain how the score was analyzed.

Because the endpoint is described as a score, an analyst would need to consider its distribution and the properties of the scale. In general, mean-based methods describe average score differences, while other methods may be suitable if the distribution is notably skewed or if assumptions of the chosen model are not reasonable. The registry identifies the parameter as a mean and dispersion as the full range, but does not report any observed means or ranges for the groups. It also does not state whether the analysis adjusted for baseline score.

Why do estimates and confidence intervals matter?

In general, an effect estimate quantifies the contrast of interest, while a confidence interval communicates uncertainty around that estimate under the analysis assumptions. The interval helps readers distinguish a precise estimate from one compatible with a broad range of effects. A significance test alone would not show the size of an effect or its clinical relevance. For this trial, comparative estimates, confidence intervals, and test results are not reported in the registry record, so these aspects cannot be assessed.

The efficacy description uses both clinical and statistical significance. Those are not interchangeable. Statistical significance concerns compatibility of data with a statistical null hypothesis under a specified procedure; clinical significance concerns whether the magnitude matters in context. A clinically meaningful threshold for score change is not reported in the registry record. Nor is a prespecified statistical threshold or detailed testing procedure. The description’s criterion therefore cannot be treated as a numerical decision rule from the available record.

What do the planning assumptions mean?

The sample-size assumptions describe a planning illustration based on the observed effect, using a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation. The effect to detect is described as a stated fraction of the observed effect. In general, sample-size planning asks how many participants per arm would be needed to detect a target effect under specified assumptions. It does not report the study’s observed efficacy, and a planning illustration is not observed power. The trial’s own sample-size justification is not reported in the registry record. The observed-effect values and resulting planning counts cannot be interpreted from the registry entries used for this explanation.

10. Multiplicity, Missing Data and Analysis Populations

The primary severity endpoint has assessments at baseline, 2 months, and 12 months, and its description refers to multiple clinical features that contribute to the score. The registry also lists change in Voice Handicap Index score at 12 months as a secondary outcome and refers to inter-surgery intervals in the efficacy description. Considering several outcomes or follow-up contrasts can raise a multiplicity question: repeated testing can increase the chance of a nominally notable finding when no adjustment or prioritization strategy is specified. That is a general statistical concern, not evidence that a particular error occurred in this trial.

The registry record does not report a multiplicity strategy, a hierarchy of tests, or which endpoint and time contrast would control the primary inference. It also does not report whether the secondary outcome was formally tested or treated descriptively. Without those details and the results, the overall evidential weight of any outcome cannot be evaluated.

Missing data are another relevant concern for outcomes assessed over time. In general, the reasons participants may miss follow-up can be related to health, treatment, or other factors. Different assumptions about such missing observations can change the analysis and its interpretation. The registry record does not report the amount or pattern of missing outcome data, reasons for missingness, imputation methods, or sensitivity analyses.

The record does not specify analysis populations, such as whether the primary analysis followed randomized assignment or was restricted according to treatment received or outcome availability. It does not describe protocol deviations or withdrawals. These omissions do not establish that particular data were missing or that any specific analysis population was used; they mean those details are not reported in the registry record.

11. 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 1% reporting threshold.

The registry’s adverse-event information gives a count of participants affected and a count at risk for each category. For cidofovir, the serious adverse-event count is 0 among 10 at risk; for placebo, it is 0 among 9 at risk. The count for participants affected by other adverse events is also 0 among 10 at risk for cidofovir and 0 among 9 at risk for placebo. These are the counts recorded, not estimates calculated from them.

Zero recorded events does not establish that an event is impossible, nor does it show that the groups have identical safety profiles. In general, uncommon events may not be observed in a study, and small observed counts provide limited information about their frequency. The registry record does not report event terms for serious adverse events, and it does not provide details about collection or follow-up procedures.

Death counts are not reported in the registry record. A missing count should not be read as a reported zero. The safety figures also do not resolve the absence of comparative efficacy results. They describe only the adverse-event counts and at-risk counts recorded in the registry.

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

The record documents a randomized, double-masked, parallel-group comparison of cidofovir injection with placebo in a trial of recurrent respiratory papillomatosis. It identifies change in Derkay Severity Score as the primary endpoint, with assessments at baseline, 2 months, and 12 months. It also lists a 12-month change in Voice Handicap Index score as a secondary outcome and refers to inter-surgery time intervals in the efficacy description.

What the record does not establish is whether the cidofovir group had a greater, smaller, or similar change than the placebo group. No outcome estimates, group summaries, confidence intervals, or test results are reported. Therefore, the record cannot support a conclusion about the size, direction, precision, or clinical importance of a treatment difference. The trial’s completed status is not a result and should not be interpreted as evidence that a stated efficacy criterion was met.

Nor does the record establish how the primary outcome was analyzed, how repeated assessments were handled, or whether missing data or multiple comparisons affected inference. These are essential details for understanding the reliability and scope of an analysis. The registry record does not report the relevant statistical plan or analysis populations.

The posted safety counts show no affected participants recorded for serious or other adverse events in the at-risk counts listed for either group. That statement is limited to the registry counts. Death counts are not reported. The safety data do not imply that risks are absent, and they do not answer the comparative outcome question.

In short, the registry describes the question and design but does not provide the comparative results needed to judge what the trial found. Any stronger conclusion would go beyond the information reported in the registry record.

13. Why This Trial Matters Statistically

This trial is statistically informative as an example of the distinction between a registered research question and an interpretable result. The record specifies a randomized comparison, a primary severity outcome, and follow-up assessments, but those design details alone cannot quantify a treatment effect. A valid interpretation requires the outcome data and a clear account of the comparison used.

The endpoint also illustrates a common measurement challenge. The Derkay Severity Score combines different manifestations of disease into a single score, with a defined range and an interpretation that higher ratings are worse. A total score can provide a compact summary, while component-level information can help explain what is changing. The registry record gives the score description but not results by total score or component, so the balance between summary and detail cannot be examined empirically.

Repeated assessments create a further statistical question: whether the comparison concerns change at a particular follow-up or the trajectory across assessments. The registry identifies the assessment times but does not report the model or contrast used. Inter-surgery intervals are mentioned in the efficacy description as well, yet no corresponding result or method is reported. These distinctions matter because analyses of scores and elapsed time may target different estimands and rely on different assumptions.

The registry’s safety counts also show why counts must be read with their denominators and reporting context. No affected participants are recorded in the listed categories, but the information does not establish absence of risk or describe unreported death counts. Overall, the record makes clear what was intended to be studied while leaving the central comparative inference unavailable. This is a limitation of the reported statistical information, not a basis for assuming a favorable or unfavorable result.

14. 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 main limitation is the absence of comparative outcome results in the registry record. There are no reported Derkay score summaries or changes, no confidence intervals or test results, and no reported results for the secondary Voice Handicap Index outcome. The inter-surgery interval comparison mentioned in the efficacy description also has no reported result. Consequently, effect direction, magnitude, precision, and clinical importance cannot be assessed.

The primary endpoint is described at baseline, 2 months, and 12 months, but the registry does not specify the primary follow-up contrast or the method for analyzing repeated measurements. It also does not report whether baseline severity was included in an adjusted analysis, how score components were handled, or whether an approach other than a mean-based summary was considered. A clinically meaningful score-change threshold is not reported.

The registry record does not report participant characteristics, the actual allocation counts in the design information, follow-up completion, treatment adherence, or withdrawals. The primary outcome population field is blank. Missing-data methods, analysis populations, protocol deviations, and sensitivity analyses are not reported. These gaps limit assessment of the study population represented in the analysis and the robustness of any result.

The efficacy description mentions both severity and inter-surgery intervals, while the listed primary endpoint is change in severity. The record does not clarify how these measures were prioritized or analyzed together. A multiplicity strategy and detailed statistical analysis plan are not reported. The trial-specific sample-size justification is also not reported; planning assumptions do not replace it.

For safety, the counts of affected participants are recorded as zero in the listed categories, but death counts are not reported. The record does not give event terms for serious events or a detailed account of adverse-event ascertainment. These reporting limits should be kept separate from the missing efficacy results.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Use of Cidofovir for Recurrent Respiratory Papillomatosis — NCT00205374.
• Registry record last updated 2019-02-26; status last verified 2019-02.
• Results first posted 2017-07-18.
• 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.

18. Record Summary

NCT00205374, titled “Use of Cidofovir for Recurrent Respiratory Papillomatosis,” is a completed phase 4, randomized, double-masked, parallel-group trial sponsored by the University of Wisconsin, Madison. The registry records enrollment of 19, a start date of 1999-11, and primary completion in 2009-12. The interventions are cidofovir injection and placebo.

The primary outcome is change in Papilloma Severity, measured with the Derkay Severity Score at baseline, 2 months, and 12 months. The secondary outcome is change in Voice Handicap Index score at 12 months. The record describes safety counts but does not report comparative outcome estimates or statistical test results. It also does not report the analysis plan, missing-data handling, or analysis populations. Thus, the registry record describes the trial design and intended outcomes, but does not provide the results needed to evaluate the treatment comparison.