Call for Life Youth ART Adherence Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Call for Life Youth ART Adherence Study (NCT04718974), a randomized na study. The primary outcome is • Viral Load Suppression.

2. Clinical Question

The central comparison is between participants assigned to the mobile-health tool with standard care and those assigned to standard care alone. This is a comparison of group outcomes, not an estimate of the effect of receiving a particular number of calls or messages. The record does not report how often participants used the system or whether adherence to the intervention was assessed. The primary endpoint is a clinical measurement at a stated follow-up time; the adherence calls and messages describe the intervention and its intended functions, not a posted primary outcome in these results.

3. Trial Design

The Call for Life Youth ART Adherence Study is registered as a randomized, parallel-group study with no masking. Its stated title describes a mixed-methods sequential study of the acceptability, effect, and cost of mobile health on ART adherence among youths in Kiryandongo. The registry lists phase as not applicable. The sponsor is Makerere University.

The registry reports enrollment of 206. It lists an intervention group receiving the Call for Life mobile-health tool with standard care and a usual-care group. For the primary viral-load outcome, the posted arm summaries give 61 participants with suppression among 96 in the intervention group, and 46 among 87 in the usual-care group. Those outcome denominators should not be assumed to describe every enrolled participant: the registry does not explain the difference between the enrollment figure and the endpoint denominators, or give a participant flow account.

The study began on 2020-08-12, reached primary completion on 2022-05-30, and is recorded as completed. The intervention could deliver interactive voice response calls or short message service. The registry describes personalized pill reminders, health messages, appointment reminders, and symptom reporting, with a secret PIN intended to protect privacy. Details about allocation generation, concealment, the timing or conduct of follow-up beyond the primary endpoint, and the planned statistical analysis are not reported in the registry record.

Randomization is intended to make groups comparable on average, while a parallel design assigns participants to one group for the comparison. Those are general features of the design; the registry does not give enough operational detail to assess how randomization was implemented or whether the analysis preserved the randomized comparison. With no masking listed, the record does not indicate that participants or study staff were blinded. It does not explain whether outcome assessors were masked.

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: The participants must have registered in either of the three study site. They should have been between 15-24 years and on ART for 6 months or less.

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.

Population: Young people 15-24 years initiating or on ART since 2019.

6. Primary Endpoint

The registry lists the primary outcome as • Viral Load Suppression, measured over • Viral load suppression at 6 months.

The primary endpoint is viral-load suppression at 6 months, expressed as a count of participants. The registry describes suppression as a viral load below 1000 copies/mL, measured using blood draws in the intervention and standard-of-care groups. The posted arm results report 61 of 96 participants in the intervention group and 46 of 87 in the usual-care group as having suppression.

Viral load is used in this study as an objective biological measure related to control of HIV infection. Unlike a self-reported adherence measure, it does not depend only on a participant’s account of taking medication or responding to reminders. It nevertheless measures a different outcome from medication-taking behavior: a viral-load result does not itself show how regularly an individual took ART, how often the mobile system was used, or why a result was observed.

The registry’s study purpose also mentions adherence measured through interactive voice responses to daily adherence calls, but the primary endpoint posted in the results is viral-load suppression. The registry lists three outcome measures, while the record does not provide posted secondary outcome results in the available outcome summary. Further information about the blood-draw procedures, assay, handling of results near the threshold, and timing windows is not reported in the registry record.

7. Results Posted in the Registry

• Standard of Care "Usual Care": 52.9% (46/87) versus 63.5% (61/96) on control; risk difference -10.7 percentage points (95% CI -24.9 to 3.6), risk ratio 0.83 (0.65–1.07); unadjusted two-proportion z-test p = 0.144.

8. Statistical Interpretation

9. Statistical Methods Explained

The posted primary outcome is binary: each participant’s viral-load measurement is classified as either suppressed or not suppressed according to the registry’s threshold. A count of participants with suppression is therefore paired with a denominator for each group. The endpoint summaries report 61 of 96 for the Call for Life group and 46 of 87 for the usual-care group. The denominators are the participants included in those summaries; the registry does not explain how they relate to enrollment or whether any endpoint measurements were missing.

What does the risk difference express?

A risk difference compares the proportion with the outcome between two groups by subtraction. It is expressed on the outcome’s probability scale, so a value of zero represents no difference between the group proportions. The registry reports an estimate of -0.107 and a confidence interval from -0.249 to 0.036. The estimate is presented as a risk difference, but the record does not specify the contrast coding in explanatory text. The signs should therefore be read as part of the posted estimate, not as a stand-alone explanation of which group has the higher result.

For a binary outcome, the risk ratio compares the outcome probabilities as a ratio, while the odds ratio compares the odds rather than the probabilities. A ratio value of one is the no-difference value for either measure. The registry reports a risk ratio of 0.832 with an interval from 0.648 to 1.068, and an odds ratio of 0.644 with an interval from 0.356 to 1.163. These measures are not interchangeable: they use different scales and can give numerically different impressions, particularly when an outcome is not rare. The reported intervals include one for both ratios.

What does the p-value say?

The unadjusted p-value is 0.144. In general, a p-value describes how unusual results at least as incompatible with a specified null hypothesis would be under that hypothesis and the assumptions of the test. It is not the probability that the null hypothesis is true, nor does it quantify the probability that the result will replicate. The registry does not report the test procedure, its assumptions, or an adjusted analysis. The label unadjusted indicates that the posted p-value is not adjusted for other comparisons.

Why use confidence intervals?

In general, a confidence interval shows a range of estimates compatible with the observed data under a statistical procedure and its assumptions. It communicates uncertainty and the range of effect sizes that remain plausible under that procedure. The risk-difference interval extends from -0.249 to 0.036. Because it crosses zero, the data do not rule out no difference on that scale. Its breadth also signals that the estimate is not highly precise. A confidence interval does not capture every source of uncertainty, including possible bias from missing data, imperfect measurement, or differences in implementation.

What does randomization contribute?

As a general principle, random assignment can reduce systematic differences between groups at the point of assignment. The study is registered as randomized, but information about sequence generation, allocation concealment, adherence to assigned groups, and baseline characteristics is not reported in the registry record. These details matter when judging whether the estimate can be interpreted as a causal comparison. The record also lists no masking. Without further information, it is not possible to assess masking of outcome assessment or the possible influence of knowledge of assignment on behavior or data collection.

What is not documented about the analysis?

The registry lists zero analyses. It does not report a model, covariate adjustment, an intention-to-treat or per-protocol population, a missing-data method, or a multiplicity plan. Those are not details that can be reconstructed from the arm counts. The posted comparison is therefore useful as a descriptive unadjusted result, but the statistical methods behind it cannot be fully evaluated from this record. The primary completion date and completed status describe the trial’s registry timeline; they do not supply missing analysis details.

The posted planning illustrations are separate from the trial’s observed results. In general, a power calculation estimates how often a specified design would detect an assumed effect under stated conditions. It is not a retrospective measure of whether the completed study had adequate power. The registry’s planning assumptions are described with the sample-size information, but the trial’s original design assumptions and sample-size justification are not reported in the registry record.

10. Confidence Intervals and Precision

The primary risk-difference estimate is -0.107, with a confidence interval from -0.249 to 0.036. In general, a confidence interval represents uncertainty around an estimate under the statistical method and assumptions used. For this comparison, the interval covers values below and above zero. That means the posted estimate is compatible with a range that includes no difference as well as differences in either direction on the risk-difference scale.

The interval is broad relative to the single point estimate, so the result does not pin down the size of the difference closely. This imprecision matters: the point estimate alone can appear more definite than the range supported by the data. The reported risk-ratio interval, 0.648 to 1.068, and odds-ratio interval, 0.356 to 1.163, also include their respective no-difference values of one. The unadjusted p-value is 0.144, consistent with the fact that the risk-difference interval includes zero under the reported comparison.

Confidence intervals describe sampling uncertainty under a statistical procedure; they do not automatically account for missing outcome measurements, differences in implementation, measurement error, or bias. The registry does not report the method used to calculate these intervals, an adjusted estimate, or how missing measurements were addressed. Consequently, precision can be assessed from the posted intervals, but not from a full account of all possible uncertainties in the study.

11. 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 sample-size planning figures are participants per arm, not total events. The registry describes them as illustrations based on the observed effect, using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The effect to detect is set at the stated fraction of the observed effect. These are planning assumptions for the illustrations; the trial’s original design assumptions and sample-size justification are not reported in the registry record.

For planning at 100% of the observed effect, the table gives 335 participants per arm for 80% power and 448 participants per arm for 90% power. For planning at 75% of the observed effect, it gives 590 participants per arm for 80% power and 789 participants per arm for 90% power. For planning at 50% of the observed effect, it gives 1,313 participants per arm for 80% power and 1,758 participants per arm for 90% power. The curve visualizes the planning relationship between assumed effect size and required sample size; it should be read using the same assumptions.

In plain language, 80% power means that a study designed under the stated assumptions would have an 80% chance of detecting the specified effect at the stated significance level if that effect were the true one. The 90% column expresses the corresponding 90% chance. A smaller effect is harder to distinguish from random variation, so the planning illustration requires more participants per arm as the assumed effect becomes smaller. These figures are not observed power for the completed trial; they are prospective planning illustrations using the observed effect as their starting point.

12. 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, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.635; treatment proportion p₁ = 0.529; average p̄ = 0.582.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.6975 = 1.3671.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.6934 = 0.5836.
4. n = (1.3671 + 0.5836)² / (-0.1067)² = 334.4, rounded up to 335 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
p0 <- 0.635416666666667                          # control proportion
p1 <- 0.528735632183908                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^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 (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(4718974)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 335 (80% power), 448 (90% power)
 75% of observed effect: n per arm = 590 (80% power), 789 (90% power)
 50% of observed effect: n per arm = 1,313 (80% power), 1,758 (90% power)
power.prop.test: 334.4 
Simulated power at n = 335 per arm: 0.800 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-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.

13. Multiplicity, Missing Data and Analysis Populations

The registry lists three outcome measures but no posted secondary outcome results in the available record. It does not report a multiplicity plan explaining whether or how statistical testing across outcomes or comparisons was controlled. Multiplicity matters in general because repeated testing can increase the chance of finding an apparently unusual result by chance. Without a prespecified hierarchy or adjustment method in the record, the unadjusted primary comparison should not be treated as evidence that other outcomes were tested or that any broader testing strategy was followed.

The registry lists zero analyses and provides no analysis population definition. In particular, it does not say whether the primary comparison used an intention-to-treat population, a per-protocol population, or another group of participants. Although the study is registered as randomized, the record does not explain whether participants were analyzed according to assignment or how any departures from assigned intervention were handled.

Missing outcome data are another unresolved issue. The primary arm summaries report denominators of 96 and 87, while enrollment is listed as 206. The registry does not provide a participant flow account, explain the relationship between those figures, report how many viral-load measurements were unavailable, or describe any imputation or sensitivity analysis. The difference between enrollment and the endpoint denominators should not be attributed to a particular reason without documentation.

These omissions do not establish that the analysis was inadequate; they mean the registry record does not allow the analysis choices to be checked. A complete assessment would require information on planned outcomes and comparisons, analysis populations, endpoint availability, and the handling of missing measurements. Those details are not reported in the registry record.

14. 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.

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: death (1.9%), road traffic accident (1.0%).

The safety summaries use denominators of 103 participants at risk in each group. The registry reports 1 serious adverse event in the Call for Life group and 2 in the usual-care group. It reports zero other adverse events in either group and deaths of 0 in the Call for Life group and 2 in the usual-care group. The safety denominators differ from the endpoint denominators, and the registry does not explain how the safety populations were defined or how they relate to the randomized groups.

The registry lists Death at 1.9% and Road traffic Accident at 1.0% among the leading serious-event terms. It does not identify which group each listed percentage refers to in the term summary, so those terms should not be assigned to an arm based on the summary alone. The serious-event counts and the death counts are separate reported fields; the record does not describe event timing, relatedness to the intervention, severity grading beyond the serious-event classification, or whether events were unique participants or event occurrences.

These figures are descriptive registry reports. They do not, by themselves, establish whether an event was caused by the intervention or whether safety differed between groups. More detailed safety definitions and case-level context are not reported in the registry record.

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

The registry’s primary result describes viral-load suppression at 6 months among participants included in the endpoint summaries. The posted counts are 61 of 96 in the mobile-health group and 46 of 87 in the usual-care group. The unadjusted risk-difference estimate is -0.107, and its confidence interval extends from -0.249 to 0.036. The interval includes zero and the estimate remains uncertain; the result should not be reduced to the point estimate alone.

This comparison does not establish that the groups are equivalent. It also does not establish a definitive difference. The confidence interval includes no difference and a range of effects on either side, while the record does not give enough information about missing data, analysis populations, or implementation to resolve those uncertainties. The reported p-value of 0.144 is a component of the statistical comparison, not a measure of clinical importance or the probability that a treatment effect exists.

The result concerns the posted primary endpoint, not every purpose named in the study title. Viral-load suppression is not the same as a direct measure of medication adherence, acceptance of the system, or cost. The registry’s brief summary describes daily adherence calls, but it does not post a secondary adherence result in the outcome summary. No cost analysis is reported in the record summarized for this comparison.

The intervention was delivered alongside standard care, and the comparator was usual care. Thus, the study question is about the added mobile-health support in that context, not about replacing ART or standard care. The registry does not provide enough detail to assess how consistently the tool was used or how generalizable the findings are beyond the study setting. These results describe the recorded comparison and its precision; they do not provide medical advice or determine what an individual should do.

16. Why This Trial Matters Statistically

This trial is statistically informative because it sets out a randomized comparison of an interactive mobile-health support system against usual care and defines a measurable primary outcome at 6 months. The outcome is based on blood draws rather than only self-reported adherence, allowing the registry to report a biological endpoint alongside an intervention designed around reminders and messaging.

The estimates also illustrate why a point estimate needs to be read with its uncertainty. The risk-difference estimate is -0.107, but its confidence interval runs from -0.249 to 0.036. The interval includes zero, and the ratio-scale intervals include one. These features make it important not to treat the observed difference as a conclusive result or to interpret an unadjusted p-value as a measure of whether the intervention is worthwhile.

Several reporting gaps are statistically important. The registry does not describe the analysis population, missing outcome handling, allocation procedures, or multiplicity plan. The outcome denominators differ from the enrollment figure, and the safety denominators differ from the primary endpoint denominators. Without participant flow and analysis details, readers cannot fully evaluate selection into the reported endpoint summaries or reproduce the comparison.

The planning illustrations also offer a useful general lesson: smaller effects require larger planned groups under the stated assumptions. Those illustrations are not the original trial’s sample-size rationale and are not observed power. Separating prospective planning from the completed study’s observed estimate helps avoid treating a retrospective calculation as proof that the study was or was not adequately powered.

17. 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 record leaves important limitations unresolved. The primary endpoint counts use denominators of 96 and 87, while enrollment is listed as 206. Participant flow, reasons for unavailable endpoint measurements, and the handling of missing data are not reported. It is therefore not possible to determine from the record whether the endpoint summaries represent all randomized participants or a subset defined by outcome availability.

The statistical analysis is not described in sufficient detail to reproduce or fully evaluate it. The record lists zero analyses and does not specify the test or model behind the unadjusted comparison, how the confidence intervals were calculated, whether adjustment for baseline characteristics was planned, or which analysis population was used. Allocation generation and concealment are also not reported, despite the study being identified as randomized. No masking is listed, and the record does not clarify whether outcome assessors were masked.

The primary outcome is a 6-month measurement, so the posted result does not describe longer-term viral-load outcomes. Details of the assay, measurement procedures, and timing windows are not reported. The study purpose includes adherence, acceptability, and cost, but the primary result available in the record addresses viral-load suppression; secondary outcomes and cost results are not posted in the outcome summary.

The safety summary has denominators of 103 in each group, which differ from the primary outcome denominators. The record does not explain the safety population or attribute the listed serious-event terms to a group. These reporting limits constrain interpretation of both the efficacy comparison and the descriptive safety figures. They should be treated as unknowns rather than filled in by assumptions.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Call for Life Youth ART Adherence Study — NCT04718974.
• Registry record last updated 2024-02-21; status last verified 2023-07.
• Results first posted 2024-02-21.
• 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.

21. Record Summary

NCT04718974, Call for Life Youth ART Adherence Study, is recorded as a completed, randomized, parallel-group study with no masking and phase listed as not applicable. The sponsor is Makerere University. The registry lists enrollment of 206, a start date of 2020-08-12, and primary completion on 2022-05-30.

The intervention was the Call for Life mobile-health tool alongside standard care; the comparator was usual care. The primary endpoint was viral-load suppression at 6 months, defined in the study description as below 1000 copies/mL. The posted counts are 61 of 96 in the intervention group and 46 of 87 in the usual-care group. The risk difference is -0.107, with a confidence interval from -0.249 to 0.036, and the unadjusted p-value is 0.144.

The registry lists three outcome measures, zero analyses, and no posted secondary outcome results in the available record. The analysis population, missing-data procedures, and original sample-size rationale are not reported in the registry record.