This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Prevalence of Genital HPV Infection in Males Following Introduction of Universal Male HPV Vaccination (NCT02003508), a registered phase not stated study. The primary outcome is Prevalence of Penile HPV Genotypes.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT02003508 |
| Phase | Phase not stated |
| Condition | Human Papillomavirus |
| Allocation | Not Stated |
| Design model | Not Stated |
| Masking | Not Stated |
| Enrollment | 345 |
| Arms in the primary outcome | n/a |
| Lead sponsor | The Alfred |
| Results posted | Yes |
2. Clinical Question
Population
Heterosexually active young men aged 17–19 years in Australia, assessed in study phases before and after introduction of universal school-based male HPV vaccination. The record describes participants as having had sexual contact with a female and no sexual contact with a male; further population detail is incomplete in the registry record.
Intervention
Eligibility to receive 4vHPV vaccination through the school-based program. The record describes eligibility, not confirmed receipt of vaccination.
Comparator
Young men ineligible for school-based vaccination because of their age when the program was introduced, assessed in the pre-program phase.
Primary question
What percentage of participants in each group had specific penile HPV genotypes detected in a single penile sample, and how precisely were those prevalence estimates measured?
3. Trial Design
This was a nonrandomized comparison of young men assessed in two calendar phases in Australia. The record labels the phases 2014–2015 and 2016–2017. The first phase corresponds to men described as ineligible for school-based vaccination because of their age at program rollout; the second corresponds to men eligible to receive 4vHPV vaccination. Both groups are described as young men aged 17–19 years.
The study’s stated aim was to examine how common HPV infection was in teenage males before and after the introduction of universal school-based vaccination of males in Australia. The registry lists enrollment as 345 and the study status as completed. The recorded study start is 2014-01, and the primary completion date is 2017-12-29.
This is not a randomized comparison. Allocation is not stated, and the registry cautions that the arms are not a like-for-like control comparison. The groups differ in program eligibility and are observed in different calendar phases. Eligibility is not the same as confirmed vaccination, and actual vaccination status is not reported in the registry record. Other differences between the groups, including possible changes over time in the population or circumstances of testing, cannot be assessed from the recorded information.
The primary outcome is prevalence of penile HPV genotypes, expressed as a percentage of participants. Each participant provided a single penile sample at one study visit, with genotypes detected using Linear Array. The record describes one primary outcome measure and lists no analyses. Further details of recruitment, sampling procedures, allocation, and the statistical analysis plan are 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
| Stage | Phase 1 (2014-2015) | Phase 2 (2016-2017) |
|---|---|---|
| STARTED | 179 | 166 |
| COMPLETED | 179 | 166 |
| NOT COMPLETED | 0 | 0 |
Analysis population for the primary outcome, as defined in the registry: All participants in group one were ineligible for school-based vaccination. All participants in group two were eligible to receive 4vHPV vaccination. All participants had experienced sexual contact with a female (either oral or vaginal sex), no sexual contact (either oral or anal sex) with a male, and had assessable penile samples.
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.
| Characteristic | Unit | Pre-vaccination Period | Post-vaccination Period | Total |
|---|---|---|---|---|
| Participants analysed | 179 | 166 | 345 | |
| Age, Continuous | years | 18.5 (17.1 to 19.9) | 18.3 (17.1 to 19.9) | 18.4 (17.1 to 19.9) |
| Sex: Female, Male: Female | Participants | 0 | 0 | 0 |
| Sex: Female, Male: Male | Participants | 179 | 166 | 345 |
| Race and Ethnicity Not Collected | Participants | — | — | 0 |
| Region of Enrollment: Australia | participants | 179 | 166 | 345 |
| Sexual contact in lifetime | Participants | 179 | 166 | 345 |
6. Primary Endpoint
The registry lists the primary outcome as Prevalence of Penile HPV Genotypes, measured over Single study visit (one time point per participant).
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | 95% Confidence Interval |
| Unit | percentage of participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint is the percentage of participants with specific HPV genotypes detected in penile samples. It is a measure of prevalence: the proportion of the assessed group with a genotype detected at the study visit. The record says that each participant provided a single penile sample and that genotype detection used Linear Array. The stated timeframe is one study visit, with one time point per participant.
Genotype-specific prevalence can describe which HPV types are detected in the sampled population. It is not, on its own, a measure of new infections over time, duration of infection, or changes within an individual. A single assessment cannot establish when an infection began or how long it persisted. Nor does a comparison by program eligibility establish the effect of vaccination receipt, because actual receipt is not reported in the registry record.
The registry identifies the endpoint’s uncertainty measure as a 95% confidence interval. Such an interval communicates the precision of a prevalence estimate under the analysis used; it is not a guarantee that the true value lies within the reported bounds. The registry record does not report the genotype-specific prevalence estimates, confidence intervals, or a list of the genotypes included in the outcome. Therefore, the endpoint’s definition is available, but its numerical results are not reported in the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry describes a relevant population-level question: how penile HPV genotype prevalence differed between young men who were ineligible for school-based vaccination and young men eligible for it. However, the registry record does not report the prevalence estimates or confidence intervals. It is therefore not possible to describe the direction, size, or precision of any observed difference from the posted results recorded.
The two groups were observed in different phases, rather than assigned at random to vaccination or a control condition. The comparison is consequently a contrast between groups defined by program eligibility and calendar period. A difference, if reported, could reflect vaccination, but could also reflect other differences between the groups or changes over time. The registry record does not provide enough information to separate these possibilities. Moreover, eligibility does not establish that an individual received vaccination; vaccination receipt is not reported in the registry record.
The outcome is prevalence at a single visit, not incidence or a longitudinal measure. It can describe the proportion with a detected genotype at the time of sampling, but it cannot show when infection occurred, whether infection was newly acquired, or whether an individual’s status changed. The stated use of a 95% confidence interval would help readers judge the statistical precision of an estimate, but confidence intervals are not reported in the registry record.
The record lists one outcome measure and zero analyses. It does not report genotype-specific findings, a comparison estimate, a p-value, a model, or an analysis population. The absence of an analysis entry is not evidence that no analysis was conducted; it means that analysis details and results are not reported in the registry record. No conclusion about the size or statistical significance of a group contrast can be drawn from the endpoint description alone.
The safety entries list zero serious adverse events, zero other adverse events, and zero deaths for each phase. These are registry counts, not a complete account of the safety of vaccination or of the study procedures. The record does not specify the adverse-event collection methods or provide a detailed follow-up description. In particular, it does not establish that no adverse events occurred outside the recorded categories or observation period.
Overall, the record documents the study question, population framing, endpoint, and phase structure, but does not provide numerical HPV results. The comparison should be read as a nonrandomized, phase-based prevalence assessment, not as a randomized estimate of the effect of vaccine receipt.
9. Statistical Methods Explained
The registry identifies the primary outcome as a percentage of participants and specifies a 95% confidence interval as its dispersion measure. The record does not include the outcome estimates or intervals, so the statistical methods can be discussed only at the level of the stated design and general interpretation.
What does prevalence mean?
In general, prevalence is the proportion of an assessed population in whom a condition or marker is present at a specified assessment. For this study, the endpoint is the percentage of participants with specific penile HPV genotypes detected in a sample collected at one visit. A prevalence estimate depends on both the number of participants with a detected genotype and the number assessed for that genotype. Those genotype-specific counts and denominators are not reported in the registry record.
Prevalence is distinct from incidence. Incidence concerns new events over time, whereas a single-visit prevalence assessment describes the presence of a detected genotype at that assessment. A one-time sample cannot determine when infection was acquired, how long it has been present, or whether it would be detected at another visit.
How should a confidence interval be read?
In general, a confidence interval gives a range of values compatible with the data and the method used to calculate the interval. Its width conveys precision: a narrower interval indicates more precise estimation, while a wider interval indicates greater uncertainty. A confidence interval does not measure the probability that the particular reported range contains the true value. Interpretation also depends on the sampling and analysis assumptions being reasonable.
The registry specifies a 95% confidence interval for the endpoint, but does not report any bounds. Readers therefore cannot assess the precision of the prevalence estimates or compare the uncertainty across genotypes or groups. The interval method, including whether it accounts for any features of sampling or analysis, is not reported in the registry record.
What does the nonrandomized comparison allow?
In general, random assignment can help balance other factors between groups, while a comparison based on eligibility and calendar phase may retain differences unrelated to the exposure of interest. Here, the groups are described as ineligible and eligible for the school-based program and are associated with different study phases. The registry explicitly notes that this is not a randomized comparison and that the arms are not a like-for-like control comparison.
Thus, even if a numerical prevalence contrast were available, it would describe the observed groups. It would not by itself isolate the effect of vaccination. Eligibility is the defining group feature in the record; actual vaccine receipt is not reported. The registry also does not report a statistical adjustment strategy or information sufficient to evaluate potential confounding. A causal interpretation would require evidence and assumptions beyond the endpoint description.
Why do genotype-specific outcomes need care?
The endpoint refers to specific HPV genotypes, which means that interpretation may involve multiple genotype-level estimates. In general, examining multiple outcomes raises a multiplicity question: when many comparisons are made, the chance of at least one apparently unusual result can increase. Methods such as prespecifying a primary comparison or adjusting inference can address this issue, but no multiplicity approach is reported in the registry record. The record lists one outcome measure and zero analyses; this does not establish how many genotype-specific comparisons were planned or performed.
What do planning illustrations mean?
In general, a sample-size calculation describes the amount of information a future study might need under stated assumptions. The planning illustration associated with this record is described as using the observed effect, a two-sided significance level of 0.05, equal allocation, and a normal approximation; it considers specified fractions of that observed effect. Such illustrations are not the study’s original design justification, and they are not observed power. They do not show the probability that the completed study detected an effect. The effect value and the resulting planning estimates are not reported in the registry record.
The registry does not report a sample-size justification, analysis model, test statistic, handling of missing observations, interim analysis plan, or prespecified statistical analysis plan. Without those details and without the outcome estimates, readers cannot independently assess the calculations or reconstruct the primary comparison.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists one primary outcome measure, prevalence of penile HPV genotypes, and zero analyses. Because the endpoint refers to specific genotypes, there may be more than one genotype-level estimate of interest, but the registry record does not give a complete genotype list, clarify which comparisons were prespecified, or describe a multiplicity strategy. No adjustment method or hierarchy of comparisons is reported in the registry record. The number of listed outcome measures alone does not resolve how multiple genotype-level results were handled.
Missing-data handling is not reported in the registry record. The endpoint description says that participants provided a single penile sample, but it does not state how many samples were usable, how missing or invalid test results were treated, or whether participants without a result were included in any denominator. The registry also does not report an analysis population definition, such as whether the analysis included all enrolled participants, only those meeting specified eligibility criteria, or only those with an interpretable sample.
The record does not describe an intention-to-treat approach, a per-protocol approach, imputation, sensitivity analyses, or exclusions from the primary analysis. These details matter because the denominator and handling of missing measurements can affect a prevalence estimate and the precision of its confidence interval. The registry’s zero analysis entries should be read as an absence of registered analysis detail, not as evidence that no analyses or missing-data decisions occurred.
Interim analyses and stopping rules are not reported in the registry record. No inference about whether such procedures were used is possible from the available information.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Phase 1 (2014-2015) | 0 | 179 | 0.0% |
| Phase 2 (2016-2017) | 0 | 166 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Phase 1 (2014-2015) | 0 of 179 |
| Phase 2 (2016-2017) | 0 of 166 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Phase 1 (2014-2015) | 0 of 179 |
| Phase 2 (2016-2017) | 0 of 166 |
The registry lists safety counts separately for Phase 1 (2014–2015) and Phase 2 (2016–2017). For Phase 1, 179 participants are listed at risk for the serious-event count and 179 for the other-event count; both recorded event counts are 0, and deaths are 0. For Phase 2, 166 participants are listed at risk for each of those event counts; both recorded event counts are 0, and deaths are 0. No serious adverse-event terms are listed.
These entries mean that the registry reports no events in the listed categories for those phase groups. They do not establish that no adverse events occurred in every sense, because the record does not describe event definitions, collection procedures, reporting completeness, or the duration and completeness of safety follow-up. The safety counts also do not provide information about vaccine receipt, so they should not be interpreted as a comparison of safety by vaccination status.
Zero recorded events should not be treated as proof of zero risk. Without event definitions and follow-up detail, the counts cannot show how comprehensively events were sought or whether unreported events occurred. They are best read as the registry’s recorded counts, not as a complete safety evaluation.
12. What the Result Does, and Does Not, Mean
This study is framed as an assessment of penile HPV genotype prevalence in young men eligible and ineligible for a school-based vaccination program. Its endpoint is a percentage measured from a single penile sample at one visit, with genotype detection by Linear Array. That design can describe the prevalence of detected genotypes in the groups assessed, if the results and denominators are available.
The registry record does not report the prevalence values, confidence intervals, genotype-specific counts, or a numerical comparison between phases. As a result, it does not establish whether prevalence was higher or lower in either group, how large any difference was, or how precisely it was estimated. It also does not report a p-value or another inferential result that would support a claim about statistical significance.
The comparison is not randomized, and the groups are defined by program eligibility in different phases. Any contrast would be an association between group membership and the measured prevalence, not a direct randomized estimate of vaccination’s effect. The record does not confirm that eligible participants received vaccination. It also cannot show individual change, new infection, or infection duration because each participant was assessed at a single visit.
The safety entries report zero serious adverse events, zero other adverse events, and zero deaths in both phases, but details about safety monitoring and follow-up are not reported in the registry record. These counts should not be generalized beyond the recorded categories and observation context.
In short, the record establishes what was intended to be measured and how the groups were framed, but its posted information does not include the numerical HPV findings needed to judge the observed prevalence or its uncertainty. It supports neither a claim that vaccination did nor did not change prevalence nor a conclusion about individual protection.
13. Why This Trial Matters Statistically
This study addresses a population-level question that is difficult to answer with a simple before-and-after contrast: whether HPV genotype prevalence in young men differed across the introduction of a universal school-based male vaccination program. The statistical challenge is not just measuring prevalence, but interpreting a contrast between groups that were not randomly assigned and were assessed in different calendar phases.
That distinction matters because eligibility, vaccination receipt, and calendar period are not interchangeable. The registry identifies eligibility as the basis for group descriptions, but does not report actual vaccine receipt. The phase-based structure also leaves open the possibility that groups differed for reasons other than vaccination. A careful interpretation therefore separates a descriptive comparison from a causal effect estimate.
The endpoint is also a useful example of the limits of one-time prevalence measurement. A sample can identify detected genotypes at an assessment, but cannot establish when infection arose or how prevalence changed for the same individuals. The confidence interval specified by the registry would help communicate precision, yet those intervals and the underlying results are not reported in the registry record.
Finally, genotype-specific outcomes raise practical questions about analysis choices, including denominators, missing samples, and multiplicity. The registry record does not give those details. The study is statistically informative as a design and reporting case: it shows why readers need outcome estimates, uncertainty intervals, analysis methods, and clear distinctions between eligibility and receipt before drawing conclusions from a population comparison.
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.
Several limitations arise from the information recorded for this study. Most importantly, the registry record does not report the primary outcome estimates, confidence intervals, group-specific denominators, or genotype-specific counts. The size, direction, and precision of the prevalence comparison therefore cannot be assessed from the posted results.
The comparison is nonrandomized and contrasts groups defined by eligibility in different phases. The registry itself cautions that the arms are not a like-for-like control comparison. Actual vaccination receipt is not reported, so eligibility cannot be treated as evidence of exposure to vaccination. The record does not provide adjustment methods or information that would allow assessment of confounding or other changes over calendar time.
Each participant contributed a single penile sample at one study visit. This limits interpretation to prevalence at that assessment and does not provide information on incidence, persistence, or within-person change. The registry describes Linear Array detection but does not report test-result denominators, how unusable samples were handled, or missing-data methods.
The population description is incomplete in the registry record, and details of recruitment and sampling are not reported. Nor are the genotype list, multiplicity approach, statistical model, analysis population, or prespecified analysis plan described. The adverse-event entries lack information about definitions and follow-up. These omissions limit both independent evaluation of the analyses and the scope of conclusions that can be drawn.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Prevalence of Genital HPV Infection in Males Following Introduction of Universal Male HPV Vaccination — NCT02003508.
- Registry record last updated 2020-03-06; status last verified 2020-03.
- Results first posted 2020-03-06.
- 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.
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18. Record Summary
The registry record describes a completed, nonrandomized study of penile HPV genotype prevalence among young men aged 17–19 years in Australia. It compares a pre-program phase of men ineligible for school-based vaccination with a later phase of men eligible to receive 4vHPV vaccination. Enrollment is listed as 345.
Participants provided one penile sample at a single study visit, and genotype detection used Linear Array. The primary endpoint is the percentage of participants with specific genotypes, with a 95% confidence interval specified as the uncertainty measure. The registry record does not report the prevalence estimates, confidence intervals, or analysis details. It also does not report confirmed vaccination receipt.
The safety entries list zero serious adverse events, zero other adverse events, and zero deaths in each phase. The record does not provide enough detail to treat these counts as a complete safety assessment.