Testing an Integrated Bio-Behavioral Primary HIV Prevention Intervention Among High-Risk People Who Use Drugs: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Testing an Integrated Bio-Behavioral Primary HIV Prevention Intervention Among High-Risk People Who Use Drugs (NCT03282890), a randomized na study. The primary outcome is Pre-exposure Prophylaxis (PrEP) Adherence Behavior.

2. Clinical Question

The clinical question is therefore about an outcome of reported adherence behavior, rather than a posted measure of HIV infection or PrEP medication use itself. The registry summary frames the study as evaluating efficacy and cost-effectiveness, but the posted primary-outcome information concerns the adherence behavior score. Cost-effectiveness results are not reported in the registry record.

3. Trial Design

The registry record describes a randomized, parallel-group trial with no masking. It lists enrollment as 237 and status as completed. The study start date is 2017-11-20, and the primary completion date is 2023-10-13. No additional information about how randomization was carried out or whether allocation was concealed is reported in the registry record.

Participants were assigned to CHRP-BB or an active control condition. The experimental arm is described as a weekly group intervention focused on HIV risk reduction and PrEP adherence. The control is described as a support group for people in recovery, matched for time and contact. The record does not report enough complete content to characterize all activities in either arm, and no masking is listed.

The primary outcome is the PrEP adherence behavior score. Although the outcome description says it is measured immediately after intervention and at 3-months, 6-months, and 9 months post-intervention, the results are reported at 9-months. The reported summaries are a mean and a 95% confidence interval for each arm.

The record lists HIV Risk Reduction Behavior as a secondary outcome. Its results are not included in the posted outcome figures described in the record. The number of analyses is listed as zero, and a two-arm continuous-outcome comparison is identified as missing or not estimable. The registry record does not report a statistical analysis plan, sample-size justification, interim analyses, or an account of which participants were included in each outcome analysis.

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 Pre-exposure Prophylaxis (PrEP) Adherence Behavior, measured over This is measured immediately post-intervention, and then at 3-months, 6-months, and 9 months post-intervention. Results are reported in the table at 9-months..

The primary endpoint is the Pre-exposure prophylaxis (PrEP) adherence behavior scale score. It is an 11-item categorical self-report measure of how confident participants feel about properly taking PrEP. The example in the registry description asks about confidence in making PrEP part of a daily routine. For each item, participants select among response categories ranging from Not at all confident to Completely confident. The item responses are summed to create a total score, with a possible range of 0-44. Higher scores indicate a better PrEP adherence behavior outcome.

This measure is used to capture reported confidence about adherence-related behaviors. That makes it a behavioral self-report endpoint, not a direct record of medication-taking or a biological measure of HIV prevention. The score can describe participants’ reported confidence, while its interpretation depends on the instrument and the outcome definition recorded by the study.

Results are reported at 9-months post-intervention, although the registry description lists other planned measurement times as well. The registry record does not explain how incomplete item responses were handled, whether the measure was validated in this study population, or how the scale score was analyzed beyond reporting the arm means and 95% confidence intervals.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous: it is a summed scale score reported as a mean for each arm. The registry record gives a 95% confidence interval as the measure of dispersion around each mean. It does not report the standard deviation, standard error, or an analysis model for the primary endpoint. A direct comparison between the randomized arms is marked as missing or not estimable.

What does a mean describe?

In general, a mean is the arithmetic average of observed scores in a group. It gives a compact description of the group’s score level, but it does not show how scores are distributed among participants. Participants may have scores close to the mean or much farther from it; the mean alone does not reveal that pattern. Here, the arm means summarize the reported PrEP adherence behavior scale at 9-months.

The scale’s interpretation is specified in the registry record: higher scores indicate a better PrEP adherence behavior outcome. The mean is therefore read in the context of this directional definition. It remains a summary of self-reported confidence, rather than an objective measure of medication-taking or a clinical event.

What does a confidence interval express?

In general, a confidence interval communicates statistical uncertainty around an estimate under the assumptions of the method used to calculate it. The interval attached to an arm mean concerns uncertainty about that mean. It does not give the range of scores among individual participants and does not directly quantify the uncertainty in the difference between arms.

To assess a randomized comparison, an analysis would usually estimate a contrast between the arms and report uncertainty for that contrast. The registry record does not report an estimable contrast for this continuous endpoint. The posted means and arm-specific intervals cannot replace a comparison-specific estimate, and the available information does not support deriving a p-value or a confidence interval for the contrast.

What does randomization contribute?

In general, random assignment is intended to create groups that can be compared without choosing treatment according to participants’ characteristics. It does not guarantee that every measured or unmeasured characteristic will be balanced, and it does not remove the need for an appropriate analysis. This record identifies the study as randomized and parallel-group, but it does not describe the sequence-generation method, allocation concealment, or the analysis population. Those details are not reported in the registry record.

The trial is listed as unmasked. The registry record does not explain whether participants, intervention staff, outcome assessors, or analysts were masked in any other way. Because the primary outcome is self-reported confidence, the absence of masking is relevant context for interpretation, but the record does not establish how it affected responses.

How should planning calculations be understood?

In general, sample-size planning calculations estimate the number of participants needed to detect a specified effect under stated assumptions. They are planning illustrations, not observed results and not evidence that a study had a particular probability of detecting its effect. The assumptions recorded for the planning illustration are a two-sided significance level of 0.05, equal allocation, and a normal approximation; the target effect is expressed as a fraction of the observed effect.

The record does not report numerical planning counts in the information available for this outcome. In addition, a planning exercise based on an observed effect is distinct from the trial’s original design justification. The trial’s own sample-size justification is not reported in the registry record. No conclusion about observed power should be drawn from planning assumptions.

Why can a comparison be not estimable?

In general, a comparison may be unavailable when the required outcome information or analysis result is absent, or when a valid estimate cannot be calculated from the posted data. The registry record explicitly identifies the two-arm continuous-endpoint comparison as missing or not estimable. It does not state why this occurred. It would be speculation to attribute the missing comparison to a particular analytic difficulty, missing-data pattern, or protocol decision.

The practical consequence is that the arm-level means can be described, but comparative precision and statistical evidence are not available. The absence of an estimate is not itself evidence that the arms are equivalent or that there is no difference. A comparison requires a reported analysis that accounts for the trial design and provides uncertainty for the contrast.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists one secondary outcome, HIV Risk Reduction Behavior, but does not provide its numerical results in the posted outcome information. It also lists zero analyses. No multiplicity strategy, such as a procedure to account for testing several outcomes or time points, is reported in the registry record. Without the analysis plan and complete outcome results, it is not possible to determine how multiple outcomes or assessment times were handled.

The primary outcome description lists measurement immediately post-intervention and at 3-months, 6-months, and 9 months post-intervention. Results are reported at 9-months. The record does not explain whether the other listed measurements were collected, analyzed, or omitted from reporting, or how the 9-month result was selected for presentation.

Missing-data methods are not reported in the registry record. The record does not say how participants with unavailable follow-up scores, incomplete scale items, or other missing information were handled. It also does not describe an intention-to-treat, per-protocol, or other analysis population for this endpoint. The arm enrollment figures do not establish how many participants contributed to the reported means.

These omissions limit assessment of the analysis. Missing-data handling can affect which observations contribute to a mean, while choices about outcomes and time points can affect how results should be interpreted. The unavailable two-arm comparison adds a further limitation: the record does not give an estimated contrast or its uncertainty. None of these unreported procedures can be inferred from the arm summaries alone.

11. Safety Results

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

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The adverse-event figures report zero serious adverse events and zero other adverse events in the CHRP-BB group, with 120 listed at risk. The control group reports zero serious adverse events and zero other adverse events, with 117 listed at risk. Deaths are reported as zero in each group. No top serious-event terms are listed.

These figures describe the counts recorded in the registry record; they should not be read as proof that no adverse experiences occurred. The record does not provide definitions, collection procedures, the period covered by these counts, or details about whether all participants were assessed in the same way. It also does not explain how events were attributed to an intervention or whether event reporting was complete.

Zero reported events in these categories is a statement about the posted counts, not a general conclusion about safety. The figures do not replace the primary endpoint or establish an intervention effect. Other safety information and more detailed event descriptions are not reported in the registry record.

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

The posted results describe mean self-reported PrEP adherence behavior scores at 9-months for the CHRP-BB and active control arms. The score is defined so that higher values indicate a better outcome. Each mean is accompanied by a 95% confidence interval, which conveys uncertainty around that arm’s mean under the analysis used.

The record does not provide an estimable two-arm comparison for this continuous endpoint. As a result, the arm summaries do not establish whether the observed scores differ statistically, how precisely any difference is estimated, or whether any difference is attributable to assignment. The absence of a reported comparison should not be interpreted as evidence that the arms are the same.

The outcome is a self-report measure of confidence about adherence behaviors. It does not directly show medication adherence, PrEP use, HIV risk reduction, HIV infection, or cost-effectiveness. Although the registry summary describes those broader aims, numerical results for the secondary HIV Risk Reduction Behavior outcome and cost-effectiveness are not reported in the registry record.

The trial is recorded as randomized, parallel-group, and completed, but information about the primary-outcome analysis population, missing data, and statistical model is not reported. Those gaps constrain how far the arm-level summaries can be taken. The posted information is useful for understanding the endpoint and its descriptive results, but it does not support a complete comparative assessment of the primary outcome.

13. Why This Trial Matters Statistically

This trial is statistically notable because it pairs a behavioral self-report outcome with a randomized comparison of an integrated intervention and an active control. The primary endpoint focuses on confidence about PrEP adherence behaviors, an outcome conceptually different from medication use or a biological measure. Keeping that distinction clear is important when interpreting what an endpoint can support.

The registry record reports arm means with confidence intervals, which allows readers to see the descriptive score summaries and their uncertainty. However, it also marks the two-arm continuous-outcome comparison as missing or not estimable. This makes the difference between describing groups and estimating a comparative effect especially important. Arm summaries alone do not provide the uncertainty around a contrast.

The measurement schedule also matters. The record lists several post-intervention assessment times, while the result is reported at 9-months. Without a statistical plan or an account of the other assessments, readers cannot assess how the reported time point fits into the study’s full analysis strategy. The record likewise does not report multiplicity procedures, missing-data methods, or the outcome analysis population.

These features make the record a useful example of how trial design, endpoint definition, and reporting completeness jointly shape statistical interpretation. The study is listed as completed, but that status does not fill gaps in the posted analysis. A transparent comparative estimate, with its uncertainty and analysis details, would be needed for a fuller statistical interpretation of the primary outcome.

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 trial-specific limitation is that the registry record does not report an estimable two-arm comparison for the continuous primary endpoint. The arm means and confidence intervals are available, but a contrast and its uncertainty are not. The record does not explain why the comparison is missing or not estimable, so the reason cannot be inferred.

The primary endpoint is self-reported confidence about PrEP adherence behavior. It is not a direct measure of medication-taking, HIV risk behavior, HIV infection, or biological prevention. The record does not provide information on validation of the scale in this population, the handling of incomplete items, or whether the reported score was calculated for every participant assigned to an arm.

The outcome description lists multiple assessment times, but results are reported at 9-months. The registry record does not explain the status of the other listed time points or the rationale for reporting this assessment. It also does not report a statistical analysis plan, multiplicity approach, missing-data method, or analysis population. These omissions prevent assessment of the full analytic context.

The intervention and control descriptions are incomplete in the registry record, limiting detailed comparison of the program content. The record lists no masking, but does not clarify which study roles were unmasked. The adverse-event counts are sparse summaries without additional information about collection, definitions, or observation periods. Finally, results for the listed secondary outcome and cost-effectiveness aim are not reported in the registry record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Testing an Integrated Bio-Behavioral Primary HIV Prevention Intervention Among High-Risk People Who Use Drugs — NCT03282890.
• Registry record last updated 2025-08-17; status last verified 2025-07.
• Results first posted 2025-08-17.
• 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

NCT03282890 is a completed randomized, parallel-group trial with no masking, sponsored by the University of Connecticut. It lists enrollment as 237 and compares CHRP-BB with an active control condition for people who use drugs at high risk of HIV.

The primary outcome is an 11-item self-reported PrEP adherence behavior scale, with a possible range of 0-44 and higher scores indicating a better outcome. The reported assessment is at 9-months post-intervention. The CHRP-BB mean is 25.9, with a 95% confidence interval of 20.4 to 31.3; the active control mean is 22.8, with a 95% confidence interval of 18.9 to 26.7.

A two-arm comparison is not reported as estimable. The record does not report the analysis plan, missing-data procedures, analysis population, or numerical results for the listed secondary outcome.