Low-Dose Peginterferon and Ribavirin to Treat Chronic Hepatitis C in Patients Infected With HCV Genotype 2 or 3: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Low-Dose Peginterferon and Ribavirin to Treat Chronic Hepatitis C in Patients Infected With HCV Genotype 2 or 3 (NCT00056862), a non-randomized phase 4 study. The primary outcome is Virological Response (Intention to Treat).

2. Clinical Question

The endpoint is a response category based on HCV RNA. Sustained virological response is defined as negative serum HCV RNA at least 6 months after treatment ends. The record also defines non-response by serum HCV RNA positivity on week 12 of treatment, and breakthrough or relapse by HCV RNA becoming negative and subsequently positive during or after treatment. Those definitions describe the categories; they do not establish how many participants fell into each category.

The comparison concerns treatment dose, but the groups were not randomly allocated. Their observed response counts, if reported, would therefore describe outcomes among the recorded groups and would not, by themselves, establish that dose caused any difference. The registry record does not report how allocation was decided, whether baseline characteristics differed, or an adjustment strategy for group differences. It also does not report the primary response counts, an effect estimate, a confidence interval, or a statistical test result. The question can be stated from the design and endpoint, but the posted record does not provide the results needed to answer it quantitatively.

3. Trial Design

This completed Phase 4 study is described as a parallel, non-randomized comparison with no masking. It concerns patients with chronic hepatitis C infected with genotype 2 or 3. The record lists an enrollment of 58 and identifies the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) as sponsor. The recorded start is 2003-03, and primary completion is 2010-01.

The low-dose group received peginterferon alfa-2a at 90 mcg per week and ribavirin at 800 mg/d for 24 weeks. The standard-dose group received peginterferon alfa-2a at 180 mcg per week and ribavirin at 800 mg/d for 24 weeks. Both descriptions specify the same treatment duration and ribavirin dose, while the peginterferon dose differs. The record does not explain how participants entered either group or whether other aspects of care were standardized.

Non-randomized allocation means group membership was not assigned by randomization, according to the registry record. Consequently, differences between groups could reflect differences in their clinical or other characteristics as well as treatment exposure. The record does not report those characteristics or describe a method for controlling potential confounding. With no masking, treatment assignment was not blinded as recorded; the record does not describe blinding of outcome assessment.

The primary outcome is titled “Virological Response (Intention to Treat)” and is measured in participants at 6 months after stopping therapy. Secondary outcomes concern the first phase decline in the logarithm of HCV RNA level, the slope of the second phase decline in HCV levels, and time to negativity. The registry lists five outcome measures and three analyses, but it does not identify the full analysis structure or provide numerical results for the primary outcome. The statistical plan, including any adjustment for baseline differences, 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.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Intention-to-treat

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 Virological Response (Intention to Treat), measured over 6 months after stopping therapy.

The primary endpoint is a participant count for virological response, assessed 6 months after stopping therapy. It is a binary outcome in the sense that the analysis concerns whether a participant meets a response category, although the registry's description also names non-response and breakthrough or relapse categories. Sustained virological response is defined as negative serum HCV RNA at least 6 months after treatment ends. Non-response is defined as serum HCV RNA positivity on week 12 of treatment. Breakthrough or relapse is defined as HCV RNA becoming negative and subsequently positive during treatment or after treatment has stopped.

HCV RNA status gives the endpoint a direct virological basis: it describes whether viral RNA is detected at the specified assessment or follows the listed response patterns. Counting participants in response categories can make a treatment outcome easier to interpret than a change in a laboratory measure alone. That is a general rationale for categorical clinical endpoints, not a claim about the findings in this study.

The registry labels the primary outcome intention-to-treat, which identifies the intended analysis population, but does not explain how missing assessments or other departures from assigned treatment were handled. Most importantly, the posted record does not state the number meeting any response category, the number analyzed, or a comparison estimate. The endpoint definition is available, but its observed result and precision are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Statistical methods describe how observations are converted into estimates and how uncertainty is assessed. They do not replace the clinical endpoint definition, and they cannot recover an outcome result that is not reported. For this study, the registry identifies a participant-count primary outcome and an intention-to-treat analysis population, but a detailed statistical plan is not reported in the registry record.

What does a participant-count endpoint mean?

A count endpoint records how many participants meet a defined outcome. For a binary outcome, each participant is classified according to whether the outcome occurred, subject to the endpoint's specific categories and analysis rules. Counts can be presented for each group, while a comparison commonly also expresses the outcome as a proportion or as a difference or ratio between groups. Those comparison measures require the underlying results and a clearly specified analysis. The registry record does not report the primary response counts or any such comparison measure.

It is important to distinguish a count from an event rate, a proportion, and an effect estimate. A count is an absolute number of participants. A proportion relates that count to the number assessed or analyzed. An effect estimate compares groups using a defined scale. The record gives the primary outcome unit as participants, but does not state the outcome counts, denominators for that analysis, or a between-group estimate. No new comparison can therefore be calculated from the record.

What does intention-to-treat identify?

Intention-to-treat names an analysis approach that aims to retain participants in the groups to which they were originally assigned or classified, even when treatment exposure changes. It is often used to preserve the comparison defined at assignment and to avoid selecting only participants who completed treatment. That is a general description. The registry gives the primary outcome population as intention-to-treat, but does not report the operational rules used in this study, how group membership was established in this non-randomized design, or how missing outcome assessments were handled. The label alone does not establish that every enrolled participant contributed an observed outcome.

Why does non-random allocation affect interpretation?

Randomization is a design method for assigning treatments by chance. It can help balance measured and unmeasured baseline factors on average, but it does not guarantee balance in every study. In a non-randomized comparison, treatment groups may differ in factors that also relate to the outcome. Statistical adjustment can sometimes address recorded differences, but it cannot automatically remove bias from unmeasured factors or from variables measured poorly. The registry does not report allocation criteria, baseline comparisons, or an adjustment method. Thus, a group contrast, even if one were available, would need cautious interpretation as an association rather than a treatment effect established by random assignment.

The study is also recorded as unmasked. Masking can reduce the influence of knowledge of treatment on some aspects of care, reporting, or assessment. Whether that influence mattered depends on the outcome and conduct of the study. The registry does not report who assessed HCV RNA or whether any outcome assessment was masked, so no more specific assessment is possible.

How should uncertainty be read?

A confidence interval is a general way to express the precision of an estimate. It gives a range of values compatible with the data and the method under stated assumptions. A narrower interval generally represents greater precision, while a wider one indicates more uncertainty. A confidence interval does not correct design bias, and it is not a guarantee that the true effect lies within the particular interval. No confidence interval for the primary response comparison is reported in the registry record.

A p-value is a measure, under a specified statistical model and null hypothesis, of how compatible the observed data are with that hypothesis. It does not measure the probability that a treatment is effective, nor does it convey the size or clinical importance of an effect. Interpretation ordinarily benefits from an effect estimate and its uncertainty, not a p-value alone. The primary-outcome p-value and testing procedure are not reported in the registry record.

What are the planning assumptions?

The record describes sample-size assumptions as planning illustrations computed from the observed effect, not as the trial's own design. They use a two-sided significance level of 0.05, equal allocation between the groups, and a normal approximation; the effect to detect is a stated fraction of the observed effect. For time-to-event illustrations, the stated quantity is the total number of events using the Schoenfeld method; other illustrations are expressed as participants per arm. These are planning conventions, not observed results or observed power.

General interpretation of a sample-size illustration depends on assumptions about the target effect, variability or event frequency, allocation, significance level, and analysis method. Equal allocation in an illustration does not change the registry's non-randomized design, and it does not establish that the actual groups were allocated equally. Since the observed primary effect and detailed illustration outputs are not reported in the record, no numerical planning result can be evaluated from the information.

Why can over-dispersion matter?

Over-dispersion is a general feature of count data in which variability exceeds what a chosen statistical model expects. If a model assumes less variability than the data contain, uncertainty can be understated and tests may appear more decisive than warranted. Methods that account for over-dispersion can produce more appropriate uncertainty estimates when the model and data support them. The primary endpoint is recorded as a binary participant count, and no over-dispersion analysis is reported. The registry does not provide enough information to determine whether this issue was relevant to any analysis.

The secondary outcomes include measures of HCV RNA decline and time to negativity. The record does not state the exact estimands, models, or test procedures for these outcomes. Different outcome types can require different statistical methods: longitudinal laboratory measurements may involve repeated observations, while time-to-event measures concern how long it takes for an event to occur and may require handling of censoring. These are general considerations, not claims about methods used in this study. The specific statistical methods are not reported in the registry record.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists five outcome measures and three analyses. It identifies a primary outcome and names secondary outcomes concerning the first phase decline in logarithm of HCV RNA level, the slope of the second phase decline in HCV levels, and time to negativity. Testing several outcomes or conducting multiple analyses can increase the chance of at least one apparently notable result arising by chance. Statistical approaches can address that issue, but the appropriate approach depends on the prespecified questions and analysis plan. Multiplicity adjustment, the testing hierarchy, and the relationship between the listed analyses are not reported in the registry record.

The primary outcome is labeled intention-to-treat, but the record does not describe how missing response assessments were handled. It does not report the number with missing outcomes, whether any imputation was used, or whether sensitivity analyses assessed alternative assumptions about missingness. Missingness can affect interpretation when the likelihood of an unavailable result is related to treatment group or outcome. Without the amount and handling of missing data, the reader cannot assess that potential influence.

The record identifies the intended population for the primary endpoint, but gives no detailed analysis population rules, exclusions, or deviations from treatment. It also does not report the statistical analysis plan, interim analyses, or prespecified decision rules. Those items should not be inferred from the endpoint label or the planning assumptions. The response counts and analysis results needed to evaluate the primary outcome 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 3% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: melanoma and death (3.7%), mastoiditis complicated by myocardial infarction, heart failure, coronary bypass surgery and death (3.7%), heroin overdose leading to death (3.7%).

The registry reports serious adverse events for 30 participants at risk in the low-dose group, with zero affected, and for 27 participants at risk in the standard-dose group, with three affected. Other adverse events are reported for two among 30 at risk in the low-dose group and one among 27 at risk in the standard-dose group. These are descriptive counts as recorded, not estimates of treatment-caused risk.

The listed serious-event terms include “Melanoma and death,” “Mastoiditis complicated by myocardial infarction, heart failure, coronary bypass surgery and death,” and “Heroin overdose leading to death,” each shown with 3.7%. These terms describe serious events in the registry listing; they should not be interpreted as evidence that the treatments caused those events. Separate death counts are not reported in the registry record.

The groups were not randomized, and their recorded at-risk counts differ. Raw adverse-event counts therefore do not provide a like-for-like causal comparison. The registry record does not describe event adjudication, exposure-adjusted safety analyses, or a statistical comparison of adverse-event frequencies. The figures are best read as a limited descriptive account, not as a complete characterization of safety or a basis for attributing events to treatment.

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

The record documents a comparison of two peginterferon alfa-2a doses, each combined with ribavirin, among patients with chronic hepatitis C infected with HCV genotype 2 or 3. It defines virological response and describes the assessment time as 6 months after stopping therapy. It also identifies the primary analysis population as intention-to-treat. These details establish what the study set out to compare and how its primary endpoint was described.

The record does not report the primary response counts, the difference between groups, a confidence interval, or a statistical test result. It therefore does not show which group had more responses, how large any difference was, or how precisely any effect was estimated. The absence of these results should not be mistaken for evidence of no difference. It means that the primary comparison cannot be evaluated from the registry record.

Even if comparative results were available, the non-randomized design would limit causal interpretation. A difference between groups could be associated with treatment dose, but could also reflect differences in the participants who received each regimen. The registry record does not report enough about group characteristics or analysis methods to assess that possibility. The design does not support treating the groups as a randomized like-for-like comparison.

The safety counts offer a description of events recorded by group, but they do not establish causation. The separate death counts are not reported, and the record does not give a broader account of safety assessment or follow-up. Nor do the planning assumptions establish observed power or provide evidence about the primary result.

In practical statistical terms, the posted information is useful for understanding the design, regimen descriptions, outcome definition, and selected safety listings. It is insufficient to determine the magnitude, direction, or precision of the primary outcome comparison. No conclusion about treatment benefit or lack of benefit follows from the missing response results.

13. Why This Trial Matters Statistically

This study is statistically informative as an example of the difference between a clearly described clinical question and an evaluable result. The registry specifies a primary virological response endpoint, an assessment time, and two dose regimens. Yet it does not report the response counts or comparative estimate. Without those results, readers cannot evaluate the primary effect or its precision, regardless of how clearly the endpoint is defined.

The non-randomized allocation is central to interpretation. In clinical comparisons, differences between groups can arise from treatment exposure and from differences in participant characteristics. Randomization is one design strategy for reducing that concern; adjustment is another possible analytical tool when relevant information is measured. The registry record does not report allocation criteria, group characteristics, or an adjustment strategy. This makes it important to distinguish an observed association from a causal treatment effect.

The record also illustrates why endpoint labels and statistical planning assumptions should not be mistaken for a complete analysis. Intention-to-treat identifies an intended analysis population, but does not explain missing-data handling or the exact analysis rules. Planning illustrations based on an observed effect are not a report of the trial's own design and are not observed power. Their assumptions cannot substitute for the underlying outcome results.

Finally, the safety listings show why counts need context. Counts and at-risk figures are descriptive, and the design does not support a simple causal interpretation of differences between groups. Taken together, the registry record is useful for learning what was compared and what information is needed to interpret a clinical trial statistically. It also makes clear that endpoint definitions, design, analysis methods, missingness, and reported estimates each contribute distinct information.

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 for interpreting this specific record is that the primary virological response results are not reported in the registry record. There are no group response counts, denominators for the primary analysis, effect estimate, confidence interval, or test result. The endpoint can be described, but its observed distribution and comparative precision cannot be assessed.

The allocation is explicitly non-randomized, and the registry record says the arms are not a like-for-like control comparison. It does not report the criteria for assigning treatment or baseline characteristics by group. Nor does it describe adjustment for confounding. Consequently, any unreported or hypothetical group contrast cannot be interpreted as a causal effect on the basis of this record.

The primary outcome is labeled intention-to-treat, but the operational definition of that population and the handling of missing measurements are not reported. The registry does not state whether response data were unavailable for any participants or how such cases entered the analysis. The methods for secondary outcomes, multiplicity control, and any sensitivity analyses are also not reported.

The record lists serious and other adverse-event counts, but does not provide event-level context beyond the selected serious-event terms, separate death counts, or a statistical safety comparison. These limitations restrict interpretation of the safety listings as well as the primary endpoint. The study's completed status does not itself supply missing results, and the planning assumptions do not resolve these gaps.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Low-Dose Peginterferon and Ribavirin to Treat Chronic Hepatitis C in Patients Infected With HCV Genotype 2 or 3 — NCT00056862.
• Registry record last updated 2013-12-06; status last verified 2013-11.
• Results first posted 2011-06-27.
• 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

NCT00056862 is a completed Phase 4, parallel, non-randomized, unmasked study sponsored by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). It concerns chronic hepatitis C in patients infected with HCV genotype 2 or 3 and lists an enrollment of 58.

The comparison is low-dose peginterferon alfa-2a, 90 mcg per week, plus ribavirin, 800 mg/d, versus standard-dose peginterferon alfa-2a, 180 mcg per week, plus ribavirin, 800 mg/d. Both regimens are described for 24 weeks. The primary outcome is virological response, designated intention-to-treat and assessed 6 months after stopping therapy.

The registry record does not report the primary response counts or comparative results. It lists secondary outcomes concerning HCV RNA decline and time to negativity, and provides limited adverse-event counts. Non-randomized allocation, missing outcome and analysis details, and absent primary results limit interpretation of the comparison.