iSTEP - an mHealth Physical Activity and Diet Intervention for Persons With HIV: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for iSTEP - an mHealth Physical Activity and Diet Intervention for Persons With HIV (NCT03123731), a randomized na study. The primary outcome is Physical Activity - Total Steps Recorded During 24 Weeks.

2. Clinical Question

3. Trial Design

The registry describes a randomized, parallel-group behavioral study with no masking. It lists three arms: a control arm, an iSTEP physical-activity intervention arm, and an iSTEP physical-activity-and-diet intervention arm. The study is marked completed, and the listed enrollment is 100. The phase is recorded as NA. The sponsor is the University of California, San Diego.

All arms involved wearing a Fitbit. The control arm did not receive additional iSTEP elements. The physical-activity arm added interactive daily text messages intended to motivate moderate physical activity and reduce sedentary behavior, including weekly goals to increase average daily step counts. The physical-activity-and-diet arm added messages promoting a Mediterranean-style diet as well as diet counseling. The record does not report the randomization method, allocation concealment, or a detailed schedule of assessments beyond the outcome timeframes it lists.

The study start date is 2018-12-01, and the primary completion date is 2023-08-15. These registry dates describe the study record, not necessarily the timing of every participant’s intervention. The posted primary outcome summaries use 25 participants in control, 24 in the physical-activity arm, and 27 in the physical-activity-and-diet arm. The registry enrollment figure and the numbers contributing to these summaries are different kinds of information; the reasons for the outcome-specific numbers are not reported in the registry record.

Because the design is unmasked, participants and study personnel were not blinded according to the registry classification. Whether outcome processing or statistical analysis was masked is not reported in the registry record. The registry identifies behavioral interventions but does not report additional details about intervention delivery, adherence, or changes in treatment during follow-up.

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 Physical Activity - Total Steps Recorded During 24 Weeks, measured over 6 months.

The primary endpoint is total steps recorded by Fitbit over 24 weeks, with a stated timeframe of 6 months. It is a continuous measure summarized as a mean and standard deviation. The registry describes zero as the minimum, gives no maximum, and states that higher scores indicate a better outcome.

Total steps across the intervention capture accumulated activity over the monitoring period. This differs from an endpoint based on a single day or a change between two selected visits: the intended measure draws on step recordings over the full 24-week period. The registry’s rationale for selecting this endpoint is not reported in the registry record. In general, continuous measurements retain information about the magnitude of values rather than reducing them to categories, although interpretation depends on how completely and consistently the measurement is recorded.

The posted group means are 1346000.0 steps for control, 1686000.0 for the physical-activity intervention, and 1685000.0 for the physical-activity-and-diet intervention. These are descriptive summaries of the participants represented in each arm’s primary outcome data. They do not by themselves establish that the intervention caused the differences: the comparison estimates and their uncertainty, the randomized design, missing outcome data, and the analysis plan all matter when interpreting the result.

7. Results Posted in the Registry

• iSTEP PA Intervention: mean 1,686,395 versus 1,345,700 on control; difference 340,695 (95% CI 256,122 to 425,268), standardized effect d = 2.28; z-test p = <0.001.
• iSTEP PA and Diet Intervention: mean 1,684,843 versus 1,345,700 on control; difference 339,143 (95% CI 274,267 to 404,019), standardized effect d = 2.81; 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.

Physical Activity - Change in Average Daily Steps Per Day Between Week 1 and Week 24

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard errors.
• Result:
  • iSTEP PA Intervention: mean 1,667 versus -1,504 on control; difference 3,171 (95% CI 720.03 to 5,622), standardized effect d = 0.82; z-test p = 0.011.
  • iSTEP PA and Diet Intervention: mean -685.00 versus -1,504 on control; difference 819.00 (95% CI -1,357 to 2,995), standardized effect d = 0.21; z-test p = 0.461.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically higher for iSTEP PA Intervention than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between iSTEP PA and Diet Intervention and the control. The interval gives the range of effects that remain compatible with the data.

Average Steps Per Day During the 24-week Intervention

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard errors.
• Result:
  • iSTEP PA Intervention: mean 10,850 versus 8,081 on control; difference 2,769 (95% CI 186.76 to 5,351), standardized effect d = 0.64; z-test p = 0.036.
  • iSTEP PA and Diet Intervention: mean 10,015 versus 8,081 on control; difference 1,934 (95% CI 8.53 to 3,859), standardized effect d = 0.54; z-test p = 0.049.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically higher for iSTEP PA Intervention than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.
  • The 95% confidence interval excludes no difference, so the mean is statistically higher for iSTEP PA and Diet Intervention than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

C-reactive Protein

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard errors.
• Result:
  • iSTEP PA Intervention: mean -63,545 versus -289,405 on control; difference 225,860 (95% CI -1,559,802 to 2,011,522), standardized effect d = 0.09; z-test p = 0.804.
  • iSTEP PA and Diet Intervention: mean -239,997 versus -289,405 on control; difference 49,408 (95% CI -1,908,599 to 2,007,415), standardized effect d = 0.02; z-test p = 0.961.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between iSTEP PA Intervention 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 iSTEP PA and Diet Intervention and the control. The interval gives the range of effects that remain compatible with the data.

The registry lists secondary outcomes spanning physical activity, cardiovascular-related measures, and GPLD1. These include changes in average daily steps, average daily steps during the intervention, C-reactive protein, cholesterol, GPLD1 levels, and associations involving physical activity and GPLD1. This broader set of outcomes addresses questions related to, but distinct from, the primary measure of total accumulated steps.

The available secondary summaries do not form a single consistent extension of the primary result. Some posted step-based comparisons are estimated in a positive direction, while other outcomes have estimates with substantial uncertainty. The pattern should be read outcome by outcome and in light of each outcome’s measurement, time frame, and available observations. Secondary findings do not change what the primary endpoint measures, and they do not establish effects on every biological or clinical domain named in the study rationale.

In general, secondary outcomes can help describe possible pathways, broader effects, or questions for later research. They are usually less definitive when many outcomes and comparisons are examined, especially if the analysis plan and any correction for multiple testing are not available. A result that appears notable among several unadjusted analyses may occur by chance more often than a single prespecified comparison would suggest. Conversely, a non-small p-value does not establish that there is no effect; it may reflect imprecision or limited information.

The registry lists 10 posted secondary outcomes, but does not report analyses for every listed measure. The reported analysis details and multiplicity strategy are not reported in the registry record. Accordingly, these secondary results are best treated as exploratory descriptive evidence alongside the primary step-count comparison, rather than as independent confirmation of a single broad clinical conclusion.

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

• Physical Activity - Change in Average Daily Steps Per Day Between Week 1 and Week 24
• Average Steps Per Day During the 24-week Intervention
• C-reactive Protein
• Change in Total Cholesterol.
• Level of GPLD1 (Phosphatidylinositol-glycan-specific Phospholipase D) Enzyme at the Baseline Visit
• Change in GPLD1 (Phosphatidylinositol-glycan-specific Phospholipase D) Enzyme Between the Baseline and 24-week Visit
• Association Between Physical Activity (PA) and GPLD1 (Phosphatidylinositol-glycan-specific Phospholipase d) at Baseline
• Association Between the Change in Physical Activity (PA) and Change in GPLD1 (Phosphatidylinositol-glycan-specific Phospholipase d) Between the Baseline Visit and 24-week Visit After the Intervention

9. Statistical Interpretation

10. Statistical Methods Explained

For a continuous outcome, a group mean describes the average recorded value among the participants included in that group summary. The primary outcome is reported as a mean with a standard deviation. In general, the standard deviation describes the spread of individual observations around a group mean; it is not the uncertainty of the mean itself. The registry’s primary summaries report standard deviations of 99290.0 for control, 187700.0 for the physical-activity arm, and 137600.0 for the physical-activity-and-diet arm.

What does a mean difference represent?

A mean difference compares the average outcome in one arm with the average in another. Here, the comparisons use control as the reference. A positive difference means the intervention arm’s posted mean is higher than the control mean for this endpoint. The recalculated differences are 340700.0 steps for the physical-activity arm and 339100.0 steps for the physical-activity-and-diet arm. These are absolute differences in total steps over the recorded intervention period, not percentage changes or differences in daily step counts.

In general, a mean difference is easiest to interpret when the outcome has a meaningful scale and is measured similarly across groups. The registry defines higher step totals as better, but does not report details about Fitbit wear time, device-data processing, or how gaps in recording were treated. A group mean can be influenced by incomplete measurement if the amount or pattern of recording differs among participants.

How should the interval estimates be read?

An interval estimate gives a range of values compatible with the observed data under the calculation’s assumptions. It communicates estimation uncertainty, rather than the range containing most individual outcomes. The posted primary comparison intervals extend from 256100.0 to 425300.0 for the physical-activity arm and from 274300.0 to 404000.0 for the physical-activity-and-diet arm. The confidence level and exact method used to construct these intervals are not reported in the registry record.

In general, an interval that is narrower indicates greater precision for the estimated mean difference, while a wider interval indicates more uncertainty. Precision depends on factors including variability and the amount of outcome information available. It should not be confused with whether an estimate is important to participants or whether the underlying measurement is complete.

What does a p-value say?

A p-value describes how compatible the observed data are with a specified statistical null model, under the assumptions of the test. The posted primary p-values are unadjusted and reported as p < 0.001 for both comparisons. In general, a small p-value is not the probability that the null hypothesis is true, nor does it tell how likely the result is to replicate. It also does not quantify the magnitude of the difference; the mean difference and its interval provide information about magnitude and precision.

The record lists no reported analyses for the primary endpoint. The comparison estimates and p-values are therefore treated as unadjusted recalculations from the posted summary statistics, not as a substitute for an analysis reported by the study investigators. The registry does not describe whether the trial’s analysis plan used a different model or addressed the allocation structure, baseline values, missing data, or multiple outcomes.

Why does outcome variability matter?

In general, greater variability among participants makes a group mean harder to estimate precisely when the amount of information is otherwise similar. The primary standard deviations differ across the posted arms, so uncertainty should be considered alongside the means and differences. The standard deviation is a description of observed spread, while a standard error describes uncertainty in an estimated quantity. The primary endpoint is summarized with standard deviations; some secondary endpoints are summarized with standard errors, so those spread measures should not be read interchangeably.

These recalculations use the posted summaries and make an unadjusted comparison of group means. They do not account for unreported participant-level information or establish that assumptions of a particular model are satisfied. The registry’s sponsor analysis does not take precedence in this case because the discrepancy flag is false; however, no sponsor-reported primary analysis is listed in the record. This distinction leaves the posted summary-based comparison useful as a descriptive statistical reading, while its relationship to the original prespecified analysis remains unreported.

11. Confidence Intervals and Precision

The primary comparison estimates are accompanied by intervals: 340700.0 steps, with limits 256100.0 and 425300.0, for the physical-activity intervention versus control; and 339100.0 steps, with limits 274300.0 and 404000.0, for the physical-activity-and-diet intervention versus control. Both intervals lie above zero. This indicates that the summary-based estimates are compatible with a positive mean difference under the calculation used, while still allowing a range of plausible values rather than identifying one exact effect.

In general, an interval expresses uncertainty about an estimated group difference. It is not a prediction interval for an individual, and it does not show the distribution of outcomes within an arm. The confidence level and the method used to calculate these interval limits are not reported in the registry record, so they should be interpreted as the posted interval estimates without assigning an unreported confidence level.

The intervals are not especially narrow in absolute step units, which leaves uncertainty about the precise size of either mean difference. At the same time, the two estimates are close in magnitude; the intervals are not a formal direct comparison between the intervention arms. A conclusion about whether the diet component changed the result would require an appropriate direct comparison and its uncertainty, which is not reported in the registry record.

The posted group standard deviations also describe substantial observed variation around the arm means. In general, a mean can summarize a group while obscuring variation among individuals. The interval for a mean difference and the standard deviation of individual observations answer different questions, so neither should be substituted for the other. The reported p-values indicate that the unadjusted recalculations are not compatible with a zero difference under their assumptions, but they do not remove uncertainty about effect size or data completeness.

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. That format fits the continuous outcomes. In general, a sample-size illustration describes the number of participants that a hypothetical study might need under stated assumptions; it is not a count of participants observed in this completed trial.

The planning illustration uses a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. It considers effects equal to 100%, 75%, or 50% of the observed effect. The trial’s own original design assumptions and sample-size justification are not reported in the registry record.

The 80% power column gives the planned number of participants per arm for a hypothetical study to have an 80% chance of detecting the stated effect under those assumptions, if that effect is the true one. The 90% power column describes the corresponding planning target for a 90% chance. In general, higher planned power requires more participants when other assumptions are unchanged. The estimates are sensitive to the observed effect used as their starting point and to the planning assumptions, so they should not be treated as a recommended design without further justification.

Rows that plan for a smaller fraction of the observed effect require more participants than rows planning to detect the full observed effect. This reflects a general statistical principle: smaller effects are harder to distinguish from random variation. The estimates are planning illustrations, not observed power. Observed power is not an appropriate summary of what the completed trial established; interpretation should instead focus on the estimated differences, their uncertainty, and the quality and completeness of the outcome data.

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 = 340695.000; pooled standard deviation σ = 149234.424.
2. n = 2 × (1.96 + 0.842)² × 149234.424² / 340695.000² = 3.0, 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 <- 340695                      # observed difference in means
sigma <- 149234.424227277                     # 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(3123731)
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 = 6 (80% power), 8 (90% power)
 50% of observed effect: n per arm = 13 (80% power), 17 (90% power)
power.t.test: 4.2 
Simulated power at n = 4 per arm: 0.767 (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 study record lists a primary endpoint and multiple secondary outcomes. It does not report a multiplicity adjustment, a hierarchy for testing outcomes, or a plan for selecting which comparisons would be treated as confirmatory. When multiple statistical tests are conducted, the chance of at least one apparently unusual result can increase. In general, adjustment procedures or a prespecified testing hierarchy can address this issue, but the appropriate method depends on the study’s aims and analysis plan. The absence of a reported strategy means the unadjusted secondary p-values should be interpreted cautiously.

The record also does not report the trial’s statistical analysis plan, the primary hypothesis test specified before outcome data were examined, or whether analyses were adjusted for baseline measures. No reported primary or secondary analyses are listed. The available comparisons are unadjusted recalculations from posted summary statistics; they do not establish which methods the investigators planned or used for the trial’s formal analysis.

Outcome-specific participant counts differ across the primary and secondary summaries. The reasons for those differences, the extent and pattern of missing data, and the methods used to handle missing or incomplete Fitbit recordings are not reported in the registry record. In general, missing outcome data can affect both the estimated group means and the comparability of the groups if the likelihood of missingness is related to activity or other participant characteristics.

The record does not state whether analyses followed an intention-to-treat approach, whether participants were analyzed according to randomized assignment, or whether a per-protocol or other analysis population was used. It also does not report how adherence, withdrawal, or protocol deviations were incorporated. These omissions limit assessment of whether the posted outcome summaries represent all randomized participants and how robust the estimated differences are to alternative handling of incomplete data. They do not negate the descriptive summaries, but they leave important aspects of the trial’s inferential approach unresolved.

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 0% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: myocardial infarction (3.1%).

The registry lists serious adverse events affecting 1 participant in the control arm, 0 in the physical-activity intervention arm, and 0 in the physical-activity-and-diet intervention arm. The corresponding numbers at risk are 32, 35, and 33. Deaths are listed as 1, 0, and 0, respectively. The record also identifies myocardial infarction as a serious adverse-event term at 3.1%.

These figures are counts reported for the registry safety record, not estimates of comparative risk adjusted for follow-up time or participant characteristics. The record does not provide enough detail to infer whether an event was caused by an intervention, when it occurred, or how the event term relates to the affected-participant count. A count of affected participants is also not necessarily the same as a count of all event occurrences if a participant could experience more than one event.

In general, safety counts should be interpreted with their denominators, event definitions, observation periods, and ascertainment methods in mind. Those details are not fully reported in the registry record. The small group counts and the limited information do not support a causal comparison between arms.

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

The posted primary summaries show higher mean total Fitbit step counts in both iSTEP intervention arms than in the control arm. The unadjusted recalculated mean differences are positive, and the reported interval limits for both comparisons are above zero. These are statistical descriptions of the recorded endpoint among the participants represented in the arm summaries.

The result does not establish that the interventions caused the observed differences. Randomization is part of the design, but interpretation also depends on how participants were followed, how step data were processed, whether outcome data were missing, and how the prespecified analysis was conducted. Several of those details are not reported in the registry record. The summary-based comparisons are not a substitute for a reported trial analysis.

The endpoint does not directly measure sedentary time, diet quality, cardiovascular disease, neurocognitive performance, or control of HIV. A higher total step count, as defined by the registry, is not evidence by itself of a change in those other outcomes. The record’s broader study rationale identifies several areas of interest, but the primary result addresses steps recorded by Fitbit over 24 weeks.

The two intervention arms each include physical-activity messaging, while one also includes diet-related elements. Because both primary comparisons are against control, they do not by themselves determine whether adding diet content changes the result. A direct comparison between the two intervention arms and its uncertainty are not reported as a primary analysis.

Finally, statistical evidence and practical importance are not identical. The p-values describe compatibility with a null model under the recalculation assumptions; they do not state whether the difference is meaningful to participants or sustainable beyond the intervention period. The registry does not report a threshold for a clinically important difference, nor does the primary endpoint establish what happened after the 24-week outcome period.

17. Why This Trial Matters Statistically

This trial illustrates a common challenge in behavioral intervention research: the measured outcome is a continuous behavior recorded over time, while the intervention combines monitoring with tailored messaging and, in one arm, diet-related content. Distinguishing the intervention’s effect from the presence of monitoring depends on the comparison structure. Because the control group also wore a Fitbit, the primary contrast concerns the added iSTEP components rather than monitoring versus no monitoring.

Statistically, the trial also shows why an estimated difference should be considered with its interval and with details of the analysis population. A small p-value can coexist with uncertainty about the exact size of an effect, and a posted summary-based calculation cannot resolve unanswered questions about missing observations or the original analysis plan. The primary outcome summaries are informative, but interpretation benefits from knowing how device recording was maintained and how incomplete records were handled.

The trial has several outcomes that connect activity with biological measures and other health-related questions. That breadth can be useful for generating hypotheses, but multiple outcomes also make a prespecified testing strategy important. Without a reported multiplicity plan, individual secondary findings carry less confirmatory weight than a clearly specified primary analysis.

Finally, planning illustrations based on an observed effect should not be mistaken for evidence that the original study was designed around that effect. The trial’s design assumptions are not reported in the registry record. Separating retrospective planning calculations from prospective design decisions helps prevent overinterpretation of unusually large or uncertain observed effects.

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.

Several limitations are specific to interpreting this record. The primary endpoint is total step count over the intervention, but the registry does not report how device non-wear, data gaps, or invalid recordings were defined and handled. It also does not report the proportion of time that participants contributed usable Fitbit data. Since a total accumulated count can depend on recording completeness, this missing measurement detail limits interpretation of the arm means.

The posted numbers contributing to the primary summary are not the same as the registry’s enrollment figure, and outcome-specific numbers also vary across secondary measures. Reasons for the differences are not reported in the registry record. Without participant flow, withdrawals, and missing-data methods, it is not possible to determine from these summaries whether the available outcome data could differ systematically from the randomized groups.

The registry labels the study randomized and unmasked, but does not report the randomization procedure, allocation concealment, or whether assessors or analysts were masked. The record also does not provide a statistical analysis plan or identify an analysis population. These omissions make it difficult to assess whether the summary-based comparisons align with the intended primary analysis.

The primary endpoint is a behavioral measure, and no threshold for a meaningful difference is reported. The posted primary comparisons do not provide a direct estimate comparing the two intervention arms. Thus, they cannot isolate the contribution of diet-related content beyond the shared physical-activity intervention components. Follow-up beyond the intervention period is not reported for the primary endpoint, limiting conclusions about persistence.

Finally, the registry lists several secondary outcomes, but does not report a multiplicity strategy or all analyses. The evidence from individual secondary comparisons is therefore less conclusive, and the broad study rationale should not be read as a set of established findings.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: iSTEP - an mHealth Physical Activity and Diet Intervention for Persons With HIV — NCT03123731.
• Registry record last updated 2024-09-19; status last verified 2024-08.
• Results first posted 2024-09-19.
• 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

The registry record describes NCT03123731, a completed randomized, unmasked, parallel-group behavioral study sponsored by the University of California, San Diego. It lists enrollment of 100 and three arms: control, iSTEP physical activity, and iSTEP physical activity and diet. All groups wore a Fitbit; the intervention arms also received text-message elements, with diet-related content in the combined arm.

The primary outcome was total steps recorded over 24 weeks. Posted means were 1346000.0 for control, 1686000.0 for physical activity, and 1685000.0 for physical activity and diet. Unadjusted recalculated comparisons versus control estimated mean differences of 340700.0 and 339100.0 steps, respectively, with both p-values reported as p < 0.001. The registry does not report a primary analysis, the original statistical plan, or methods for missing data and multiplicity, so these summary-based results should be interpreted with those limitations in mind.