Pre-exposure Prophylaxis (PrEP) Adherence Enhancement Guided by iTAB and Drug Levels for Women: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Pre-exposure Prophylaxis (PrEP) Adherence Enhancement Guided by iTAB and Drug Levels for Women (NCT02584140), a na phase 4 study. The primary outcome is Adherence to PrEP.

2. Clinical Question

In statistical terms, the record describes an adherence-assessment question within a single group, rather than a randomized comparison of two interventions. It can identify the intended target population, the program components, and the biomarker-based definition used for the primary outcome. It does not establish how adherence under AEGIS compared with adherence under usual care or another program, because no such comparator is recorded.

The study also lists treatment-emergent adverse events, HIV infections, and correlates of PrEP adherence as secondary outcomes. Their outcome results, beyond the adverse-event counts described in the safety discussion, are not reported in the registry record. Thus, the central statistical question is whether the program's adherence measure was achieved among participants, but the posted record does not give the primary count needed to answer that question descriptively.

3. Trial Design

NCT02584140 is a Phase 4 study recorded as completed, with enrollment of 136. The study started in 2016-05 and its primary completion date is 2019-05-15. The sponsor is the University of California, Los Angeles. Its official title describes multimodal interventions to improve adherence to oral tenofovir/emtricitabine as pre-exposure prophylaxis in women in Southern California.

The design is listed as single group, with allocation recorded as not applicable and masking recorded as none. The sole arm is AEGIS, and the registry says all participants were assigned to it. The interventions include text messaging, adherence counseling, and daily oral PrEP. The study description also names drug-level monitoring as part of the adherence-support program. The record does not describe a randomized allocation process or a masking procedure.

These design features matter for interpretation. With no separate control group, changes or outcomes observed among participants cannot be directly contrasted with outcomes under another assigned intervention. A single-group result can describe what was observed in the enrolled group, but does not by itself separate program effects from other explanations, such as changes over time or differences among participants. The registry does not report a comparator condition or a between-group treatment estimate.

The primary outcome timeframe is Week 4 to Week 48. Although the study is complete, the registry record does not report a full analysis plan, the primary outcome count, or the analysis population. It also does not report the sample-size justification, planned interim analyses, or further details of follow-up and outcome collection. The study's enrollment figure describes the number enrolled, not necessarily the number contributing data to every outcome.

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 Adherence to PrEP, measured over Week 4 to Week 48.

The primary endpoint is titled Adherence to PrEP and is defined as the count of participants whose tenofovir diphosphate (TFV-DP) concentrations in dried blood spots are suggestive of 6-7 doses per week. The timeframe is Week 4 to Week 48. The endpoint therefore uses a drug-level biomarker as an indicator of medication-taking, rather than relying only on a participant's report of adherence.

In general, a biomarker can provide an objective measure related to medication exposure, while a threshold translates the measured concentration into a category intended to represent a dosing pattern. That category is an operational definition: it describes how the study classified the measure, rather than directly documenting each dose taken. The registry gives the adherence interpretation associated with the concentration but does not report the concentration cut-off, laboratory procedures, or how measurements across the timeframe were combined.

A count of participants can communicate how many met the endpoint definition, but its interpretation depends on the denominator and on how missing measurements were handled. The registry record does not report the primary count, the number with evaluable measurements, or a confidence interval. Consequently, 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 interpretation begins by separating the design question from the measurement question. The design is single group: all participants were assigned to AEGIS, with allocation recorded as not applicable and masking recorded as none. The measurement question is how many participants met the specified biomarker-based adherence definition. A single-group count can describe observed outcomes, but it does not estimate a contrast between assigned treatments. Such a contrast would require a comparison condition and a clearly defined comparative analysis, neither of which is reported in the registry record.

What does a count endpoint describe?

The primary outcome is a count of participants whose TFV-DP concentrations in dried blood spots were suggestive of 6-7 doses per week, over Week 4 to Week 48. A count records the number classified as meeting an outcome definition. To interpret it fully, readers also need to know the denominator: for example, how many participants had a measurement that could be classified. The registry reports enrollment of 136, but does not report the primary outcome count or its analysis denominator. Enrollment alone should not be substituted for the number with an evaluable endpoint.

The outcome is based on a biomarker threshold, which maps laboratory measurements to an adherence category. In general, this approach can make the outcome less dependent on recall than a self-reported dosing measure. At the same time, a threshold-based category is not a direct record of every dose. Interpretation depends on the validity of the threshold, the measurement schedule, and the rules for handling repeated or missing measurements. Those details are not reported in the registry record beyond the stated concentration interpretation and timeframe.

How should uncertainty be understood?

In general, a confidence interval describes a range of values compatible with the data under the assumptions of a statistical method. For a single-group count, an interval could help convey how precisely the observed outcome rate is estimated, provided the necessary count, denominator, and analysis method are available. The registry does not report a primary count, an interval, or the method used to estimate uncertainty. No numerical statement about the precision of the adherence outcome can therefore be made.

A p-value, when used, addresses how unusual data would be under a specified statistical model and null hypothesis. It does not measure the size or clinical importance of an effect, and it is not a substitute for an estimate and its uncertainty. No primary-outcome p-value or null hypothesis is reported in the registry record. The recorded number of analyses does not reveal what test was used or whether that analysis concerned the primary endpoint.

What can a single-group analysis establish?

In general, a one-group analysis can summarize the observed distribution or count in the group studied. It cannot isolate the effect of an intervention from other factors that may influence the outcome, because it has no contemporaneous comparison group. For this trial, the registry describes a multimodal program and one assigned group. It does not provide a control-group outcome, a randomized contrast, or an adjusted estimate comparing groups. Any interpretation should therefore remain descriptive unless additional analysis details are reported elsewhere in the registry record.

Adjustment for participant characteristics can sometimes address measured differences in a comparative study, but it cannot create the missing randomized comparator in this record. The registry does not report an adjusted model, covariates, or a model-based primary estimate. It would be speculative to infer which statistical methods were used from the endpoint type or the study phase.

What do the planning assumptions mean?

The registry's planning illustration is described as using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the target effect defined as a stated share of the observed effect. These are planning assumptions, not a description of this trial's single-group design. The record does not report a sample-size justification for the actual study, and planning illustrations must not be read as observed power or as evidence that the study could detect a particular effect. They answer a hypothetical design question under stated assumptions; they do not add an observed outcome or replace a missing analysis.

In general, power is a design property calculated for an assumed effect and analysis, whereas observed data describe what occurred in the study. A planning calculation cannot show that a treatment effect was present, nor can it establish the precision of the primary endpoint after data collection. In this case, no primary adherence estimate or interval is reported, so the planning assumptions do not resolve the main interpretive gap.

Why do missing analysis details matter?

For a binary classification such as meeting an adherence threshold, interpretation can depend on whether all scheduled measurements were available, how measurements were grouped across the timeframe, and how participants without classifiable measurements were treated. In general, excluding participants with missing outcomes can make a result differ from an analysis that accounts for missingness in another way. The registry does not report the missing-data method, the number with observed measurements, or the rules used to form a participant-level outcome. No assumptions about these procedures should be inferred.

The registry records four outcome measures and one analysis. These counts do not identify which outcome was analyzed, whether the analysis was descriptive or inferential, or whether there were additional planned analyses. They also do not establish whether multiplicity was considered. A reader would need the statistical analysis plan or fuller results to assess those choices. The registry record does not report those details.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists four outcome measures, including the primary PrEP adherence outcome and secondary outcomes concerning treatment-emergent adverse events, HIV infections, and correlates of PrEP adherence. It records one analysis. Those counts do not specify which outcomes were included in that analysis, how outcomes were ordered for inference, or whether any multiplicity adjustment was planned or used. A correction for multiple testing, a hierarchical testing procedure, or another approach is not reported in the registry record.

Multiplicity matters in general when several outcomes or hypotheses are tested: considering many results can increase the chance that at least one appears notable by chance. Whether and how that issue applies depends on the analysis plan, the intended claims, and the relationship among outcomes. The available record does not provide enough information to determine the statistical approach, so no claim about control of multiplicity is warranted.

Missing-data handling is also not reported for the primary endpoint. The record does not state how many participants had usable dried-blood-spot measurements, how incomplete follow-up was handled, or whether the analysis included all enrolled participants. The enrollment of 136 does not establish the denominator for the adherence count. The registry also does not report a defined analysis population, such as an intention-to-treat or per-protocol population, or criteria for inclusion in any analysis.

These omissions affect both the interpretation of a count and its precision. They do not demonstrate that missing data or multiplicity problems occurred; they mean that the registry record does not describe how those issues were addressed. A detailed analysis plan and outcome results are not reported in the registry record.

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 2% reporting threshold.

Most frequent non-serious adverse event terms

The registry reports 0 participants with serious adverse events among 136 at risk, 0 deaths, and 64 participants affected in the other adverse-event category among 136 at risk. These are counts in the AEGIS group, not a comparison of risks between treatment groups. Because the study has a single group, the figures do not provide a controlled estimate of whether the program changed the frequency of adverse events.

The serious-event count is a participant count, not a description of event types or severity beyond the serious classification. No top serious-event terms are listed. The other-event figure indicates that participants were counted as affected, but the registry record does not provide event-level details, timing, duration, severity, or attribution. It also does not clarify the relationship between that figure and the separately named secondary outcome of treatment-emergent adverse events. The registry does not report additional detail that would resolve this distinction.

In general, safety counts need context such as the definitions used, observation time, event types, and the number actually followed for safety. The registry gives 136 at risk for each reported category, but does not provide further follow-up detail in the record summarized. These counts should be read as descriptive registry figures, not as proof that no serious events occurred beyond the recorded classification or as evidence of a comparative safety profile.

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

The record describes a completed, single-group program combining daily oral PrEP, adherence counseling, text messaging, and drug-level monitoring. It defines a primary adherence endpoint based on TFV-DP concentrations in dried blood spots suggestive of 6-7 doses per week during Week 4 to Week 48. These details explain what the study set out to assess and how the primary outcome was framed.

The record does not report the observed primary adherence count, its denominator, or an estimate of uncertainty. It therefore does not establish how many participants met the endpoint definition or how precisely that count was estimated. The absence of a reported result is not evidence that the endpoint was or was not achieved; it leaves the primary result unknown in the registry record.

Even with an observed count, the single-group design would support a description of outcomes among participants rather than a controlled comparison. No other group is recorded, so the study cannot estimate a difference against a control condition from these data. Nor does the record report sufficient methods to assess adjustment, missing data, or inferential testing. Any broader claim about what caused an outcome would go beyond the statistical information recorded.

The safety figures are likewise descriptive: the registry reports 0 participants with serious adverse events, 0 deaths, and 64 participants affected in the other adverse-event category. They do not establish a comparative safety effect, and detailed event information is not reported. The secondary outcome results for HIV infections and correlates of PrEP adherence are not reported in the registry record.

Thus, the record is informative about the study's design, interventions, and intended measurement, but it does not support a numerical conclusion about the primary adherence result. It should not be read as establishing either benefit or lack of benefit. The key statistical distinction is between a stated outcome definition and a reported, interpretable outcome estimate; the former is present, while the latter is not.

13. Why This Trial Matters Statistically

This trial raises several useful statistical issues for researchers evaluating adherence-support programs. First, it uses a biomarker-based outcome rather than describing adherence only through self-report. Such an endpoint can make the measurement strategy more explicit, because the registry states what concentration pattern is interpreted as suggestive of 6-7 doses per week. At the same time, the measurement rule and the participant-level aggregation method are important to interpretation, and those details are not reported in the registry record.

Second, the design makes the distinction between describing an outcome and estimating an intervention effect especially clear. A single group can yield a count of participants meeting an outcome definition, but a comparison group is needed to estimate how outcomes differ under another condition. The registry records one group and does not report a primary outcome count, so neither a descriptive adherence result nor a comparative effect is available from the record.

Third, the endpoint spans Week 4 to Week 48. A timeframe covering repeated or extended assessment brings practical analytical questions: how measurements are scheduled, how they are combined, and what happens when some measurements are missing. Those questions are general considerations for longitudinal biomarker outcomes; the registry does not report the procedures used in this study.

Finally, the record illustrates why safety counts, outcome definitions, and statistical analyses need to be distinguished. Serious-event and other-event counts are not substitutes for the primary adherence result, and a listed analysis count does not identify the method or conclusions. For clinical researchers, these distinctions help prevent a study's design description from being mistaken for evidence about the magnitude, precision, or comparative effect of an intervention.

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 most direct limitation of the available registry information is that the primary endpoint is defined but its observed count is not reported. The record also does not report the endpoint denominator, an interval estimate, or a primary-outcome p-value. Without these, the adherence outcome cannot be quantitatively summarized or assessed for precision.

The design is single group, with no separate comparator. This limits causal and comparative interpretation even if a descriptive outcome result were available. The record does not report a detailed statistical plan, the method used for the one recorded analysis, or whether any covariate adjustment was performed. It also does not report a sample-size justification for the actual study, planned interim analyses, or a defined analysis population.

Measurement and follow-up details are limited. The registry identifies TFV-DP concentrations in dried blood spots and gives the interpretation and timeframe, but does not report the threshold value, measurement schedule, laboratory procedures, or how repeated measurements were combined. It does not report how missing or unusable measurements were handled, or how many participants had evaluable primary-outcome data.

Safety reporting is also limited to participant counts. The record lists no serious adverse-event terms and does not provide details for the other adverse-event category, such as types, timing, severity, or attribution. Results for the listed secondary outcomes of HIV infections and correlates of PrEP adherence are not reported in the registry record. These are limitations of what the record documents; they do not establish that the procedures or results were absent from other study materials.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Pre-exposure Prophylaxis (PrEP) Adherence Enhancement Guided by iTAB and Drug Levels for Women — NCT02584140.
• Registry record last updated 2021-07-08; status last verified 2021-06.
• Results first posted 2020-05-27.
• 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

NCT02584140 is a completed Phase 4, single-group study sponsored by the University of California, Los Angeles. Enrollment was 136. The study examined a program for women in Southern California combining daily oral PrEP, adherence counseling, text messaging called iTAB, and drug-level monitoring.

The primary outcome was a count of participants with TFV-DP concentrations in dried blood spots suggestive of 6-7 doses per week during Week 4 to Week 48. The registry record does not report that count, its denominator, or an inferential result. No comparison group is recorded.

The registry reports 0 participants with serious adverse events, 64 affected in the other adverse-event category, and 0 deaths. It does not report the primary analysis method, missing-data handling, analysis populations, or results for the listed secondary outcomes of HIV infections and correlates of PrEP adherence.