Electronic SBI(RT) for MSM in Argentina: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Electronic SBI(RT) for MSM in Argentina (NCT05542914), a randomized na study. The primary outcome is Acceptability of eSBI.

2. Clinical Question

3. Trial Design

This was a randomized, parallel-group pilot trial with no masking, according to the registry. It was part of a larger sequence of development and feasibility work. Phase 1 included focus groups, individual interviews, and a pilot study; Phase 2 was the pilot randomized trial of e-SBI. The record lists electronic screening and brief intervention and an assessment-only condition as behavioral interventions. Assessment-only participants completed screening instruments without the brief intervention.

The planned setting was Nexo Asociacion Civil, a community partner in Buenos Aires, where participants were awaiting HIV testing. The e-SBI was delivered on a tablet and was intended to combine screening for substance use and sexual risk behavior with tailored Motivational Interviewing. The broader project also assessed the feasibility and acceptability of implementing the adapted Men's Health Project, described as a four-session Motivational Interviewing intervention.

The registry describes the study as a pilot intended to establish processes and procedures for a later, larger efficacy trial. It also states that the pilot was not powered to detect differences between arms; examining preliminary changes in substance use and sexual risk behavior was exploratory. The registry reports enrollment of 274, a start date of 2022-11-30, primary completion on 2025-02-12, and a completed status.

The record does not report the original sample-size justification, detailed allocation procedures, or a full statistical analysis plan. The posted acceptability results span Phase 1 and Phase 2 groups, and the registry states that the three groups are different samples not meant to be compared. This distinction matters when interpreting numerical contrasts among their means.

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.

Before assignment: This study has two phases with separate samples of participants. Phase 1 focused only on acceptability of the intervention. Phase 1 data were not pre-specified to be compared to Phase 2 data. Phase 2 was a pilot RCT. Participants were assigned 3:1 to e-SBI or Assessment Only after baseline assessment. No significant events occurred between enrollment and assignment. Counselors were not considered enrolled in the study and, therefore, are not included in the Enrollment Number.

Phase I: Pilot Study

Phase II Base Line

Phase II: 6-Month Follow up

Analysis population for the primary outcome, as defined in the registry: This is the number of Nexo clients to whom a recruitment flyer was given during the conduct of the Phase 2 RCT. This outcome is not relevant to Phase 1 participants.

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 Acceptability of eSBI, measured over Baseline.

The primary endpoint is described as the mean overall acceptability score. Acceptability is a measure of participants' assessment of whether an intervention is acceptable to them; it is not itself a measure of changes in substance use, sexual risk behavior, or HIV outcomes. Such a measure can help assess whether an intervention is suitable for further development and integration into a testing process.

The measurement differed across groups. For Phase 2 participants and Phase 1 pilot study participants, the score came from one overall question on the Theoretical Framework of Acceptability questionnaire, with responses from 1 (not at all) to 4 (totally). For Phase 1 individual interview participants, the registry describes a multi-item scale rated from 1 (not at all) to 5 (a lot), with a negatively worded item reverse-scored before calculating the mean. The description calls this a six-item scale but lists seven prompts; that discrepancy is not clarified in the registry record.

Because the groups used different acceptability measures and were not intended to be compared, their means should be read as descriptive results for their respective samples rather than as a common-scale treatment contrast. The record does not report a primary endpoint result for the assessment-only group.

7. Results Posted in the Registry

• Phase 2: e-SBI Arm Participants: mean 3.61 versus 4.77 on control; difference -1.16 (95% CI -1.32 to -1.00), standardized effect d = -2.09; z-test p = <0.001.
• Phase 1 Pilot Study Participants: mean 3.77 versus 4.77 on control; difference -1.00 (95% CI -1.17 to -0.83), standardized effect d = -2.53; z-test p = <0.001.

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.

Entry Into MHP

• 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:
  • Assessment Only: 1.9% (1/53) versus 0.7% (1/147) on control; risk difference 1.2 percentage points (95% CI -2.7 to 5.1), risk ratio 2.77 (0.18–43.56); unadjusted two-proportion z-test p = 0.449.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Assessment Only and the control. The interval gives the range of effects that remain compatible with the data.

The secondary outcomes concern entry into the Men's Health Project, completion of that program, and Motivational Interviewing proficiency. The posted results include an entry outcome; results for completion and proficiency are not reported in the registry record. The reported entry comparison is exploratory and does not show a clear statistical distinction between the groups under the unadjusted analysis.

These outcomes address implementation and engagement with a follow-up intervention, rather than the primary acceptability measure itself. They therefore add a different kind of information: whether participants enter or complete a service and whether intervention delivery meets a proficiency criterion. They do not directly establish that e-SBI changes substance use or sexual risk behavior. The record identifies those behavior changes as exploratory aims but does not report corresponding results.

Unadjusted secondary results carry less weight than a prespecified primary analysis because they may be one of several outcomes examined, and the record does not describe a multiplicity strategy. When many outcomes are tested, the chance of seeing an apparently notable result by chance can increase. General statistical principle: adjustment procedures or a clear hierarchy of outcomes can help manage that risk, but no such approach is reported. The pilot design and limited event information also mean that secondary estimates may be unstable. These findings are best treated as preliminary signals for planning rather than definitive evidence about implementation or behavioral effects.

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

• Entry Into MHP
• MHP Completion
• MI Proficiency

9. Statistical Interpretation

10. Statistical Methods Explained

The primary measure is a continuous outcome summarized by its mean and standard deviation. A mean gives the arithmetic average of participants' scores, while the standard deviation describes how spread out the scores are around that average. These summaries describe the observed responses; by themselves they do not show how precisely the mean estimates a broader population value.

The measurement details are important for interpreting those summaries. Phase 2 e-SBI participants and Phase 1 pilot study participants answered one overall acceptability question on a scale from 1 to 4. Phase 1 individual interview participants completed a different multi-item assessment on a scale from 1 to 5. The record says that one negatively phrased item was reverse-scored before averaging. The resulting means are not directly comparable as if they came from the same instrument and scale. The registry also describes the interview assessment as six items while listing seven prompts, and does not resolve that inconsistency.

The comparison summaries accompanying the primary outcome are labelled as simple recalculations from posted summary statistics. They present unadjusted differences between group means, confidence intervals, and p-values. An unadjusted comparison does not account for other participant characteristics or study features. The registry record lists no sponsor-reported analyses, and the recalculated comparisons should therefore be understood as exploratory numerical contrasts rather than as the trial's reported confirmatory findings. The discrepancy flag is false, so there is no stated conflict requiring a sponsor analysis to take precedence.

A confidence interval gives a range of values compatible with the data under the assumptions of the calculation. Its width reflects precision: a narrower interval indicates greater precision, while a wider interval leaves more uncertainty about the underlying contrast. A p-value evaluates how compatible the observed data are with a specified no-difference model, under the analysis assumptions. It does not express the probability that the no-difference model is true, nor does it establish whether a difference is important.

For the secondary outcome of entry into the Men's Health Project, the posted comparison is expressed as a risk difference, with an unadjusted interval and p-value. A risk difference compares the event proportions between groups. The result is exploratory, and the confidence interval spans values on both sides of zero, so the data are compatible with no difference as well as with differences in either direction. The registry does not report a sponsor analysis for this outcome.

The posted sample-size illustrations are planning calculations based on fractions of an observed effect. They assume a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. These are assumptions for the illustrations, not documented assumptions from the original trial design. No calculation of observed power should be inferred from the results. General statistical principle: power is the probability that a study will detect an effect of a specified size under stated assumptions if that effect is real. It is a design property, not a measure of whether the observed result is reliable.

When event counts are sparse, estimates of group differences can be imprecise and depend strongly on a small number of observations. General statistical principle: over-dispersion occurs when outcome variability is greater than a model assumes, which can make standard errors too small if not accounted for. The registry does not report whether over-dispersion was assessed; this is a general consideration, not a description of an analysis conducted in this trial.

The record does not report a detailed model specification, covariate adjustment, missing-data method, or a defined analysis population for these outcomes. It also does not report interim analyses or a multiplicity adjustment. In the absence of those details, the displayed unadjusted calculations should not be read as evidence that these issues were addressed through a prespecified statistical plan.

11. Confidence Intervals and Precision

The posted summaries report standard deviations for the three acceptability means, but the registry does not give confidence intervals for the individual group means. The recalculated mean-difference comparisons do include intervals. For the contrast between Phase 2 e-SBI participants and Phase 1 individual interview participants, the interval runs from -1.32 to -1.0. For the contrast involving Phase 1 pilot study participants, it runs from -1.168 to -0.832 when expressed to three decimal places. These intervals quantify statistical uncertainty under the recalculation assumptions, but they do not address the fact that the samples and measurement instruments differ.

For entry into the Men's Health Project, the posted risk-difference interval runs from -0.027 to 0.051. Because it includes zero, it is compatible with no group difference as well as with differences in either direction. Its span also indicates that the result is not precise enough to distinguish among a range of plausible effects.

Confidence intervals describe uncertainty in an estimate, not the range of individual participants' scores or outcomes. A narrow interval can indicate a precise estimate, but precision does not resolve bias, differences in measurement, or limitations in the study design. The registry does not report intervals for every posted outcome, and it does not provide a complete analysis plan. Accordingly, the intervals from simple recalculations should be interpreted as statistical summaries, not as a full account of uncertainty in the trial's findings.

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. They use the observed effect as a reference and show alternative planning scenarios for detecting 100%, 75%, or 50% of that effect. Each scenario has a column for 80% power and a column for 90% power. In plain terms, the 80% column gives the estimated number of participants per arm under which the assumed effect would be detected in 80% of repeated studies using the stated assumptions. The 90% column uses a higher chance of detection and consequently calls for more participants per arm.

The listed assumptions are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The effect to detect is the stated fraction of the observed effect. Smaller target effects require more participants because they are harder to distinguish from random variation. These calculations are planning illustrations based on the observed effect, not the trial's original design justification; the original design assumptions are not reported in the registry record.

These figures are not observed power. They describe hypothetical future designs under the stated assumptions, and they should not be used to claim that the pilot had a particular probability of detecting an effect. The registry explicitly describes the pilot as not powered to detect differences across arms.

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 = -1.160; pooled standard deviation σ = 0.554.
2. n = 2 × (1.96 + 0.842)² × 0.554² / -1.160² = 3.6, rounded up to 4 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 <- -1.16                      # observed difference in means
sigma <- 0.554336798087846                     # 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(5542914)
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 = 4 (80% power), 5 (90% power)
 75% of observed effect: n per arm = 7 (80% power), 9 (90% power)
 50% of observed effect: n per arm = 15 (80% power), 20 (90% power)
power.t.test: 4.8 
Simulated power at n = 4 per arm: 0.694 (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 record does not report a multiplicity adjustment or a hierarchy specifying how the primary and secondary outcomes were to be tested. This matters because several aims and outcomes are described, including acceptability, feasibility, entry into the Men's Health Project, completion, and Motivational Interviewing proficiency. When multiple statistical tests are conducted, unadjusted p-values do not account for the increased chance of at least one apparently notable result arising by chance. The record does not report a confirmatory testing strategy, so the posted secondary results should be treated as exploratory.

The record also does not report a missing-data method, the amount of missing outcome data, or how incomplete questionnaires were handled. This is relevant to acceptability measurement because the registry notes that, in Phase 2, the assessment was programmed to occur at the end of the intervention and many participants did not realize that the acceptability assessment was there. The extent to which this affected completion or interpretation is not reported in the registry record.

Analysis populations are not fully described for the posted outcomes. The registry gives group sizes for the acceptability summaries and the secondary entry outcome, but it does not specify a general intention-to-treat or per-protocol approach, nor does it explain how participants with missing values were treated. Allocation concealment, detailed randomization procedures, interim analyses, and the trial's original sample-size justification are also not reported in the registry record. These gaps limit assessment of whether the numerical results reflect prespecified methods and how robust they are to incomplete data or analysis choices.

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 5% reporting threshold.

The registry reports serious adverse events and other adverse events separately for Phase I, Phase II intervention, and Phase II control groups. For each listed group, the record reports zero serious adverse events, zero other adverse events, and zero deaths. The corresponding at-risk counts are 74 for Phase I, 147 for the Phase II intervention group, and 53 for the Phase II control group.

These figures mean that no events of the listed types were recorded in those groups in the registry results. They do not establish that the true risk is zero, and they do not rule out events that were not captured or reported. The record does not list serious adverse event terms. It also does not provide further detail about event ascertainment or the period covered by these safety counts, so broader conclusions about safety cannot be drawn from these counts alone.

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

The posted results describe acceptability scores from several stages of intervention development and a pilot trial. They indicate that participants in each reported sample provided measurable acceptability ratings, but the values should not be treated as direct comparisons across groups because the instruments differed and the samples were not intended to be compared. The record does not provide a primary acceptability comparison against the assessment-only group.

The exploratory result on entry into the Men's Health Project does not establish a difference between the groups. The registry also does not report results for completion of that program, Motivational Interviewing proficiency, or changes in substance use and sexual risk behavior. Consequently, these results do not establish whether the intervention changed those behaviors, affected HIV outcomes, or improved health.

The trial's stated role was to develop the electronic intervention and assess feasibility and acceptability in preparation for a larger efficacy trial. This is different from testing whether the intervention produces a definitive clinical or behavioral benefit. The posted simple recalculations offer statistical contrasts, but they cannot resolve differences in measurement, sampling, or the absence of a reported confirmatory analysis.

These findings can inform questions for future research, such as consistent outcome measurement, assessment timing, and implementation procedures. They should not be used as medical advice or as a basis for conclusions about individual care. The registry record does not report enough information to determine how generalizable the results are beyond the study setting and participant groups.

17. Why This Trial Matters Statistically

This trial is statistically informative because it combines intervention development with a pilot randomized evaluation. Those aims require different kinds of evidence. Acceptability and feasibility can indicate whether an intervention and its delivery process merit refinement, while a later efficacy study would be needed to estimate behavioral effects with a design suited to that question. The registry explicitly describes the pilot as not powered to detect differences across arms.

The outcome measurement also illustrates why scale definitions matter. A mean score has meaning only in relation to the questions, response options, and scoring rules used to create it. Here, the individual interview group used a different acceptability assessment from the Phase 2 and Phase 1 pilot groups. Presenting their means side by side does not make them equivalent measures.

The record further highlights the distinction between exploratory recalculations and trial-reported analyses. Unadjusted contrasts can help readers understand the numerical data, but they are not a replacement for a prespecified analysis plan. Missing details about analysis populations, incomplete data, multiplicity, and the original design assumptions restrict how strongly the results can be interpreted.

For future studies, the reported assessment-timing issue and the differences in measurement are practical as well as statistical considerations. A clearly specified common outcome, analysis plan, and sample-size rationale would make later estimates easier to interpret. The pilot's value lies in informing that next stage, not in settling the efficacy question.

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 primary acceptability results come from different samples and different measurement instruments. The registry explicitly says the groups are not meant to be compared, yet the posted recalculated contrasts use the Phase 1 individual interview group as a reference. Those contrasts are therefore especially difficult to interpret as intervention effects. The Phase 1 individual interview scale is also described inconsistently: it is called six-item, while seven prompts are listed.

The Phase 2 assessment occurred at the end of the intervention, and the registry notes that many participants did not realize the acceptability assessment was there. The record does not quantify the consequences for completion or explain how missing responses were handled. This can limit confidence in how representative the recorded acceptability scores are of all participants in that phase.

The trial was a pilot and was not powered for between-arm differences. Its exploratory entry outcome has sparse event information, and the registry does not report results for the other listed secondary outcomes or for the behavioral changes described as exploratory aims. No detailed statistical analysis plan, missing-data approach, multiplicity strategy, analysis population, or original sample-size justification is reported. These limitations mean that the posted findings are best read as developmental and exploratory rather than definitive.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Electronic SBI(RT) for MSM in Argentina — NCT05542914.
• Registry record last updated 2026-10-21; status last verified 2026-09.
• Results first posted 2026-10-21.
• 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

NCT05542914 is a completed randomized, parallel-group pilot trial of electronic screening and brief intervention for men who have sex with men awaiting HIV testing in Buenos Aires, Argentina. The project aimed to develop the e-SBI, assess its feasibility and acceptability in the testing process, and examine implementation of the Men's Health Project. The posted primary outcome is mean overall acceptability, but results come from different groups using different measures. The record also reports an exploratory outcome on entry into the follow-up program. It does not report results for several other listed outcomes or behavioral changes. The findings are developmental and exploratory, consistent with the stated purpose of informing a later efficacy trial.