HIV/STI Prevention for Drug-Involved Couples: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for HIV/STI Prevention for Drug-Involved Couples (NCT01285349), a randomized na study. The primary outcome is Number of Unprotected Acts of Intercourse.

2. Clinical Question

The registry describes two related questions. The first compares each HIV risk-reduction condition with the wellness promotion control on unprotected intercourse and biologically confirmed STIs over follow-up. The second concerns whether the couple-based intervention would be more like the individual-based intervention; the available summary ends before stating the full hypothesis. The specific statistical contrast for that second question is not reported in the registry record.

The primary measure is the number of unprotected acts during a 90-day timeframe, recorded at the 12-month assessment. The secondary outcome concerns participants with biologically confirmed chlamydia, gonorrhea, or trichomoniasis during the past 12 months. These outcomes address different aspects of HIV/STI risk: reported sexual behavior and biological confirmation of selected infections. The posted results do not establish that either measure captures every aspect of risk or prevention.

3. Trial Design

This was a randomized, parallel-group trial registered as NCT01285349, titled HIV/STI Prevention for Drug-Involved Couples. The registry lists Columbia University as sponsor, the phase as NA, an enrollment of 564, and the study status as completed. The recorded start was 2005-11 and primary completion was 2009-10. The registry lists sexually transmitted infections as the condition.

Participants were assigned to one of three conditions: couple-based HIV prevention, individual HIV/STI prevention, or couple-based wellness promotion. The couple-based prevention condition consisted of 7 sessions. The individual condition also consisted of 7 sessions and was described as identical in content to the couple intervention, but provided to the index participant alone. The control was a 7-session couple-based stress-reduction intervention intended as an attentional control. The registry describes the study as randomized and parallel, with quadruple masking. Which specific people or roles were masked is not reported in the registry record.

The trial’s target population was HIV-negative, concordant heterosexual couples with drug involvement in one or both partners. The registry says recruitment occurred primarily through street outreach in drug-using locations. It does not provide further detail about recruitment eligibility, the allocation sequence, concealment, or the timing of assignment beyond the randomized designation.

The registry reports a primary endpoint of unprotected acts of intercourse at 12 months, with the measure’s timeframe described as 90 days. It also lists a secondary outcome of participants with biologically confirmed STIs over the past 12 months. Although the registry describes a 12-month follow-up period in its summary, the specific timing and completeness of outcome assessments are not reported in the registry record. The trial’s original sample-size assumptions and detailed statistical analysis plan are also 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:

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 Number of Unprotected Acts of Intercourse, measured over 90 days.

The primary endpoint is the mean number of unprotected acts of intercourse in the 90-day timeframe assessed at 12 months. It is a continuous measure: each participant’s reported count contributes to a group mean. The registry labels the outcome as a number of unprotected acts at 12 months while specifying a 90-day timeframe, so the assessment time and the period covered by the report should be kept distinct.

This behavioral endpoint is used because the trial’s stated aim includes reducing unprotected intercourse. It measures reported behavior rather than directly establishing whether an infection occurred. The secondary biological outcome addresses a different question by counting participants with laboratory-confirmed chlamydia, gonorrhea, or trichomoniasis over the past 12 months. Neither measure alone represents every possible sexual-health outcome.

For the primary endpoint, the registry posts a mean and standard deviation for each arm, along with mean-difference comparisons against the wellness promotion control. A mean difference describes how far apart the group averages are, in the original outcome units. The standard deviation describes variation among observations within an arm; it is not the uncertainty interval for the group mean or for the comparison. The registry record does not report the exact instrument, respondent, or procedures used to collect the behavioral measure.

Self-reported behavior can be affected by how participants recall or disclose events, while biologically confirmed infection is a distinct outcome with its own ascertainment process. The record does not provide enough detail to assess those measurement procedures. Interpretation should therefore stay with the stated endpoint and the posted summaries rather than treating the behavioral measure as a direct biological outcome.

7. Results Posted in the Registry

• Couple-based HIV Prevention: mean 12.90 versus 19.70 on control; difference -6.80 (95% CI -11.99 to -1.61), standardized effect d = -0.28; z-test p = 0.010.
• Individual HIV/STI Prevention: mean 18.20 versus 19.70 on control; difference -1.50 (95% CI -7.48 to 4.48), standardized effect d = -0.05; z-test p = 0.623.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Number of Participants With Biologically Confirmed STIs (i.e., Chlamydia, Gonorrhea, and Trichomoniasis)

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Couple-based HIV Prevention: 1.8% (3/170) versus 1.8% (3/163) on control; risk difference -0.1 percentage points (95% CI -2.9 to 2.8), risk ratio 0.96 (0.20–4.68); unadjusted two-proportion z-test p = 0.959.
  • Individual HIV/STI Prevention: 1.1% (2/184) versus 1.8% (3/163) on control; risk difference -0.8 percentage points (95% CI -3.3 to 1.8), risk ratio 0.59 (0.10–3.49); unadjusted two-proportion z-test p = 0.557.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Couple-based HIV Prevention and the control. The interval gives the range of effects that remain compatible with the data.
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Individual HIV/STI Prevention and the control. The interval gives the range of effects that remain compatible with the data.

The secondary outcome concerns the number of participants with biologically confirmed chlamydia, gonorrhea, or trichomoniasis during the past 12 months. Across the two intervention-versus-control comparisons, the posted case counts are close, and the estimated risk differences are small. Both uncertainty intervals include no difference. This overall pattern does not provide a clear separation between either prevention condition and wellness promotion on the biological endpoint.

The secondary endpoint complements the primary behavioral measure, but the two outcomes should not be expected to move in lockstep. The primary endpoint records reported unprotected acts during a 90-day period at the 12-month assessment; the secondary outcome records biological confirmation over the past 12 months. They differ in measurement, timeframe, and statistical scale. A result on one does not confirm or invalidate the other, and the record does not report an analysis linking individual behavioral changes to infection outcomes.

Unadjusted secondary findings generally carry less weight than a prespecified primary analysis because the more outcomes and comparisons considered, the greater the opportunity to observe an apparently notable result by chance. Whether and how the trial planned to address that issue is not reported in the registry record. The registry also lists no reported analyses for the secondary endpoint, so the posted calculations should be treated as descriptive, unadjusted comparisons rather than as a complete inferential analysis.

There are differences in the posted group counts between the primary and secondary outcome summaries. The registry does not explain those differences, nor does it report the analysis populations or missing-data procedures. That limits direct comparison of the endpoints. The secondary results therefore offer context about the recorded biological outcome, but they do not independently establish that the behavioral pattern is replicated or that the interventions differ in infection incidence.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Number of Participants With Biologically Confirmed STIs (i.e., Chlamydia, Gonorrhea, and Trichomoniasis)

9. Statistical Interpretation

10. Statistical Methods Explained

The registry posts group-level summary statistics and unadjusted contrasts. It does not list reported analyses, and the detailed statistical analysis plan is not reported in the registry record. The explanations below distinguish what can be read from these summaries from general statistical principles.

What does a mean difference represent?

For a continuous endpoint such as the number of unprotected acts, a mean difference is the control-group mean subtracted from the intervention-group mean in the posted comparison. A negative estimate means the intervention arm’s posted average is lower than the control arm’s average; a positive estimate would mean it is higher. The estimate remains in the outcome’s original units, so it can be read as a difference in average acts over the stated timeframe.

The posted comparisons use the couple-based wellness promotion condition as the control. They do not directly compare the two HIV prevention conditions with each other. This matters because separate estimates against a shared control are not a substitute for a direct intervention-versus-intervention contrast. A difference between the two estimated effects would need its own estimate and uncertainty calculation, which are not posted.

How should the standard deviations be read?

A standard deviation describes the spread of individual observations around an arm’s mean. Larger within-arm spread means participants’ outcome values vary more widely. It is not a confidence interval and does not describe only uncertainty in the mean difference. For a mean comparison, the standard error and sample sizes contribute to uncertainty in the estimated contrast. The posted arm summaries give standard deviations, and the comparison summaries give standard errors for each group mean.

In general, continuous outcomes with substantial variation may have estimates that are less precise unless there is enough information to distinguish the group averages. The registry’s summaries do not report an adjusted model, the distribution of individual outcome values, or a diagnostic assessment of the assumptions used for a mean-based comparison. It is therefore not possible to evaluate from the record whether an alternative model would have been preferred.

What do the confidence intervals and p-values add?

A confidence interval expresses statistical uncertainty around an estimated contrast under the method used to calculate it. For the primary outcome, the couple-based comparison’s interval lies on the negative side of zero; the individual-based comparison’s interval crosses zero. An interval crossing zero indicates that the compatible values include no mean difference, but it does not prove that there is no difference. An interval that excludes zero does not, by itself, establish practical importance or resolve bias and analysis concerns.

The p-values posted for these continuous comparisons are unadjusted. In general, a p-value measures how unusual data at least as incompatible with a null model would be if that model and its assumptions held. It is not a measure of the magnitude of an effect, a measure of the probability that a finding is due to chance, or a substitute for the confidence interval. The record does not report whether these comparisons were prespecified or whether any multiplicity procedure was planned.

How is the secondary outcome different?

The secondary outcome is a count of participants with biologically confirmed STIs, rather than a mean of a continuous measurement. The posted risk difference compares the proportion with the outcome in an intervention arm against the proportion in the control arm. A negative risk difference means a lower observed proportion in the intervention arm; a positive value means a higher one. Its confidence interval describes uncertainty in that difference under the calculation method.

For binary outcomes, the number of recorded cases and the group denominator both affect precision. When only a small number of cases are recorded, estimates may be unstable and intervals broad. In general, sparse data can make relative measures such as risk ratios especially uncertain. The registry posts risk-difference comparisons and also relative-measure summaries, but it does not report a fitted model or a detailed analysis method for this outcome. The results should not be interpreted as more precise than their intervals indicate.

What does an unadjusted comparison leave out?

An unadjusted contrast is a direct summary comparison that does not account for other variables in a model. Random assignment is intended to support fair comparisons, but the registry does not report the allocation process in detail, an analysis population, baseline balance, or adjustments for baseline outcome values or other covariates. It is not possible to determine from these records whether the posted calculations account for clustering within couples, repeated measurements, or other design features.

General statistical practice distinguishes the randomized assignment from the population included in an endpoint analysis. A complete interpretation needs to know how participants were handled if they did not complete follow-up, whether all randomized participants were analyzed in assigned groups, and how missing outcomes were addressed. Those details are not reported in the registry record. The group counts shown for the primary and secondary outcomes differ, but the record does not explain why; the difference should not be attributed to a particular cause without further information.

The registry’s summary describes a 12-month follow-up period, but no repeated-measures model, time-to-event analysis, or change-from-baseline estimate is posted. The primary result should therefore be interpreted as the posted endpoint comparison, not as a trajectory over time. The registry does not report interim analyses or stopping rules. It also does not provide a protocol-level sample-size justification, so the trial’s original design assumptions cannot be reconstructed from the posted planning illustration.

11. Confidence Intervals and Precision

The primary couple-based comparison has a mean difference of -6.8 acts, with a 95% confidence interval from -11.99 to -1.61. The interval is entirely below zero, indicating that the posted estimate favors a lower average count in the couple-based prevention arm under the unadjusted comparison. The range remains meaningful for interpretation: the data are compatible with different magnitudes of lower mean count, not only with the single point estimate. The interval does not account for unreported analysis choices, missing-data handling, or multiplicity.

For the individual-based comparison, the mean difference is -1.5 acts, with a 95% confidence interval from -7.482 to 4.482. It includes zero and allows values in either direction. This is evidence of limited precision for determining the direction or size of the difference, not evidence that the arms are identical. The interval’s width should be considered alongside the point estimate and the endpoint’s variability.

In general, a confidence interval is a range produced by a statistical method that would cover the underlying quantity at its stated rate over repeated applications of that method, if its assumptions hold. It does not mean there is a stated probability that the fixed effect lies inside this particular interval. The interval also does not capture systematic error, such as biased measurement or differential missingness.

The STI outcome is based on few recorded cases, and its risk-difference intervals include no difference for both comparisons. That pattern signals substantial uncertainty about the size and direction of those contrasts. A lack of a clearly separated estimate is not a demonstration of equivalence. No equivalence margin or noninferiority margin is reported in the registry record, and the record does not identify a precision target for either endpoint.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not total events. The registry’s planning note distinguishes time-to-event outcomes, which would use total events, from other outcomes, which use participants per arm; the posted outcomes in this trial are not time-to-event outcomes. Read each row as an illustration based on the stated fraction of the observed effect, and each power column as a different target probability of detecting an effect of that size under the planning assumptions.

The stated assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect used is the listed fraction of the observed effect. The original sample-size assumptions for the trial itself are not reported in the registry record. These planning calculations are not the trial’s own design justification.

In plain language, the 80% power column gives the illustrative number of participants per arm associated with an 80% chance of detecting the specified effect under those assumptions; the 90% power column gives the corresponding illustration for a 90% chance. These are planning targets, not guarantees. Rows using a smaller fraction of the observed effect require more participants per arm because smaller differences are harder to distinguish from random variation. This pattern is visible across the listed rows, including for the sparse biological outcome.

The sample-size curve should be read as a planning aid that shows how required group size changes as the assumed effect changes, not as a record of enrollment or outcome precision for a new study design. The calculations rely on the observed effect as their reference, so they can be sensitive to how uncertain or unusually large or small that observed estimate is. They should not be treated as a recommendation without design-specific assumptions about the population, outcome, analysis, and follow-up.

This is not observed power. Observed power is not a useful substitute for reading the estimated effect and its confidence interval; the illustrations instead show hypothetical planning requirements under the listed assumptions.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -6.800; pooled standard deviation σ = 23.972.
2. n = 2 × (1.96 + 0.842)² × 23.972² / -6.800² = 195.1, rounded up to 196 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- -6.8                      # observed difference in means
sigma <- 23.9723518994095                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(1285349)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 196 (80% power), 262 (90% power)
 75% of observed effect: n per arm = 347 (80% power), 465 (90% power)
 50% of observed effect: n per arm = 781 (80% power), 1,045 (90% power)
power.t.test: 196.1 
Simulated power at n = 196 per arm: 0.799 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

The registry describes multiple questions, two intervention-versus-control comparisons, and more than one outcome. The primary endpoint is unprotected acts of intercourse; the secondary endpoint is participants with biologically confirmed STIs. It does not report a hierarchy for testing, a multiplicity adjustment, or a plan for interpreting results across outcomes and contrasts. Any adjustment or prespecified testing strategy is not reported in the registry record.

Multiplicity matters because repeated statistical tests increase the chance that at least one result will appear unusual under a collection of null hypotheses. In general, adjustment procedures can limit that issue, but they may change the interpretation of individual p-values and confidence intervals. Since the registry does not describe such a procedure, the posted p-values should be read as unadjusted and not as a family-wise confirmatory conclusion.

Missing-data handling is not reported in the registry record. The record does not say how participants without a 12-month assessment were treated, whether incomplete reports were excluded, how any missing values were imputed, or whether sensitivity analyses were conducted. It also does not identify whether the posted summaries reflect an intention-to-treat population, a per-protocol population, or another analysis set. Those omissions limit assessment of potential bias if follow-up or outcome availability differed by arm.

The primary and secondary outcomes have different arm counts in the posted summaries, but the reason is not reported in the registry record. The primary endpoint shows an individual-arm count of 163, while the secondary endpoint shows an individual-arm count of 184. The record does not explain the discrepancy, so it should not be attributed to attrition, exclusions, or any other mechanism.

The registry lists zero reported analyses. It does not provide an interim-analysis plan, stopping boundaries, or details of the statistical models used. Nor does it report whether couple-level clustering, repeated assessments, or baseline measures were considered. These are not grounds to assume a particular flaw; they are limits on what can be evaluated from the posted record.

15. 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 1% reporting threshold.

The registry’s serious adverse event summary lists zero affected participants in each of the three arms and zero deaths in each arm. It also lists zero participants affected by other adverse events in each arm. The recorded at-risk counts are 190 for couple wellness promotion, 190 for couple-based HIV prevention, and 183 for individual HIV/STI prevention. No serious adverse event terms are listed.

These are registry-reported safety figures. A count of zero affected participants means no affected participants were entered in the posted summary; it does not, by itself, establish that no event occurred outside the reporting definitions, observation period, or captured records. The registry does not provide further detail about event definitions, collection methods, exposure time, or whether the at-risk counts represent the same population used for the efficacy outcomes.

The safety figures should be read separately from the trial’s behavioral and STI outcomes. They do not establish comparative safety beyond the recorded summary, and the differing at-risk counts should not be reconciled with other outcome group sizes without additional information. The record does not list serious adverse event narratives or category-specific explanations.

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

The posted primary summaries show a lower mean number of unprotected acts in the couple-based HIV prevention arm than in the couple-based wellness promotion arm, with an unadjusted confidence interval that does not include zero. The individual-based prevention comparison has a smaller estimated difference and a confidence interval that includes zero. Those findings describe the recorded group summaries; they are not a complete account of the trial’s analysis because the registry lists no reported analyses and does not provide the statistical plan.

The results do not establish that the couple-based intervention is superior to the individual-based intervention. Both are compared with the same control, and no direct estimate between the prevention arms is posted. They also do not establish a difference in biologically confirmed STIs. The secondary outcome has few recorded cases and imprecise comparisons. The behavioral and biological outcomes answer related but distinct questions.

A confidence interval that excludes zero is not a measure of clinical importance. The registry does not provide a threshold for a meaningful change in unprotected acts, nor does it state a minimum clinically important difference. Likewise, an interval that includes zero is not proof of no effect or equivalence. No equivalence or noninferiority framework is reported.

The registry’s summaries cannot establish how well the interventions were delivered, whether effects persisted beyond the recorded follow-up, or whether the results apply to populations outside the stated target group. The record does not provide enough information about missing data, outcome measurement, analysis populations, baseline differences, or model choice to assess those considerations fully.

These results are statistical descriptions, not medical advice. They should not be interpreted as a recommendation for any individual or as a claim that either intervention does or does not prevent HIV or other infections. The trial’s stated outcomes and posted comparisons support a limited reading of group-level differences, with uncertainty and reporting gaps kept in view.

17. Why This Trial Matters Statistically

This trial raises a design question that is statistically distinct from asking whether prevention content differs from a control: whether delivering that content to a couple is different from delivering it to one partner. The three-arm structure provides two comparisons against the wellness promotion condition, but the registry does not post a direct couple-versus-individual estimate. That distinction is important whenever readers compare results from separate contrasts against a shared control.

The behavioral primary outcome and the biological secondary outcome also illustrate why endpoint selection matters. A self-reported count of unprotected acts and a biologically confirmed STI outcome capture different parts of the prevention question. Their timeframes differ as well. Statistical interpretation must account for each outcome’s scale, measurement process, and uncertainty rather than treating one as a proxy for the other.

The trial record also shows why confidence intervals are useful alongside point estimates. One unadjusted primary contrast has an interval that excludes zero, while another spans values in both directions; the sparse secondary endpoint is less precise. Looking only at point estimates or p-values would conceal some of that uncertainty. The posted record nevertheless leaves important questions unanswered about analysis populations, missing data, multiplicity, and the trial’s original planning assumptions.

For biostatisticians and clinical researchers, the central lesson is to separate the randomized design from the quality and completeness of outcome reporting. Randomization is relevant to causal interpretation, but posted aggregate summaries alone do not reveal how follow-up, outcome availability, or analysis decisions were handled. Transparent reporting of those choices is needed to evaluate the strength and scope of a trial’s conclusions.

18. 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 registry provides aggregate arm summaries rather than participant-level data or a detailed analysis report. It does not report baseline characteristics, so the degree of baseline balance cannot be assessed from this record. It also does not provide the behavioral measurement instrument, the biological testing procedures, or details of how outcomes were collected and verified.

Posted group counts differ between the primary and secondary outcome summaries, including for the individual prevention arm. The registry does not explain why. Without an account of analysis populations and missing outcomes, these counts cannot be interpreted as evidence of a specific follow-up or exclusion pattern.

The record does not report whether the analysis accounted for the couple-level structure of the intervention or any repeated observations. It does not describe model diagnostics, covariate adjustment, baseline outcome handling, or sensitivity analyses. Because the registry lists no reported analyses, the unadjusted comparisons cannot be checked against a fuller inferential analysis.

The summary’s second hypothesis is incomplete, and no direct couple-based versus individual-based comparison is posted. The registry also does not report the original sample-size justification, protocol-level analysis plan, multiplicity procedure, interim monitoring, or stopping rules. These absences limit assessment of whether the posted contrasts were prespecified and how uncertainty across the study’s questions was intended to be handled.

Finally, the trial’s results apply most directly to the stated target population and setting: HIV-negative, concordant heterosexual couples with drug involvement in one or both partners, recruited primarily through street outreach in drug-using locations. The registry record does not establish generalizability to other populations, recruitment settings, or follow-up periods.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: HIV/STI Prevention for Drug-Involved Couples — NCT01285349.
• Registry record last updated 2019-01-14; status last verified 2018-07.
• Results first posted 2019-01-14.
• 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.

22. Record Summary

NCT01285349, HIV/STI Prevention for Drug-Involved Couples, is recorded as a completed, randomized, parallel-group trial sponsored by Columbia University. The registry lists an enrollment of 564, phase NA, a start date of 2005-11, and primary completion in 2009-10. The target population was HIV-negative, concordant heterosexual couples in which one or both partners were drug-involved.

The three conditions were couple-based HIV prevention, individual HIV/STI prevention, and couple-based wellness promotion. The primary endpoint was the number of unprotected acts of intercourse at the 12-month assessment, with a 90-day timeframe. The secondary outcome was participants with biologically confirmed chlamydia, gonorrhea, or trichomoniasis over the past 12 months.

The registry posts unadjusted arm summaries and comparisons, but lists no reported analyses. The primary couple-based contrast has a confidence interval excluding zero; the individual-based contrast and both secondary comparisons are less conclusive. Missing-data procedures, the analysis population, multiplicity handling, and the trial’s original sample-size assumptions are not reported in the registry record.