W8Loss2Go: mHealth Weight Management Strategy: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for W8Loss2Go: mHealth Weight Management Strategy (NCT02689154), a na na study. The primary outcome is Body Mass Index (BMI) z -Score.

2. Clinical Question

Other stated questions concerned whether participants could withdraw from problem foods, eliminate daytime snacking, and reduce daily meal portion size using a wireless food scale. These are listed as secondary outcomes, but their results are not reported in the registry record. The study therefore describes questions the intervention was intended to address, rather than a controlled test of whether it produced an effect relative to an alternative. Without reported outcome estimates, the magnitude and precision of any change in BMI z-score cannot be assessed from the registry record.

3. Trial Design

The registry identifies W8Loss2Go as a completed, single-group study with an enrollment of 18. It lists the intervention as a device and names one arm, the W8Loss2Go App. Participants in that arm were to complete all stages of the mobile health intervention. The study was unmasked, and allocation is listed as not applicable. These design features mean that the record does not describe random assignment or a concurrent control group.

The sponsor was Children’s Hospital Los Angeles. The registry lists the study start as 2016-04 and primary completion as 2017-09. The primary outcome was BMI z-score, measured at baseline and 6 months. Its primary outcome population is described as 18 youth who completed the app intervention. The record lists four outcome measures, including the primary outcome and the named secondary outcomes concerning problem foods, daytime snacking, and meal portion size.

Those details describe the registered structure, but they do not establish the analytic procedures used. The statistical analysis plan, any prespecified method for comparing baseline and follow-up values, and any interim analyses are not reported in the registry record. The registry lists zero analyses. It also does not report whether all enrolled participants contributed data at each time point, or how missing measurements were handled.

Because the design has one intervention group, any before-and-after description would concern change over time among participants, not a randomized treatment contrast. Such change can be influenced by factors beyond the intervention. The registry record does not supply a control-based estimate that would separate the intervention from other explanations for observed change. No sample-size justification specific to the study is 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.

Before assignment: Newly referred patients were pre-screened for eligibility prior to their first clinic visit. YFAS-c was utilized to screen for traits of food addiction. Inclusion criteria included age 12-18 years and positive YFAS-c. Exclusion criteria were: obesity co-morbidities known psychiatric illness or developmental delay, and the inability to read English.

Overall Study

Analysis population for the primary outcome, as defined in the registry: 18 youth that completed the app intervention

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: Of the 50 eligible adolescents approached, 18 elected to participate in the app intervention

6. Primary Endpoint

The registry lists the primary outcome as Body Mass Index (BMI) z -Score, measured over Baseline and 6 months.

The primary endpoint is BMI z-score, a standardized measure of BMI relative to a reference distribution. The registry describes a z-score as the number of standard deviations a value is from the mean: zero is equal to the mean, negative values are below the mean, and positive values are above it. The outcome is listed at baseline and 6 months, with the primary population described as 18 youth who completed the app intervention.

The registry’s direction convention is important when interpreting a change: a negative change value represents a decrease in BMI and is described as a better outcome, while a positive change represents an increase and is described as a worsening outcome. This direction is specific to the registry’s stated endpoint interpretation. It does not, by itself, indicate how large a change would be meaningful.

In general, a standardized measure can help describe where an individual’s value lies relative to a reference distribution. A z-score is not a direct measure of the intervention’s effect, and its interpretation depends on the reference used and the analysis population. The registry record does not report the reference details, observed baseline or follow-up values, a mean change, or an uncertainty interval. It also does not report a threshold for a clinically meaningful change. Thus, the endpoint definition is available, but the size and precision of the observed result are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies BMI z-score as a continuous primary measure, describes the primary summary as a mean, and names standard deviation as its dispersion measure. It does not report the actual estimates or the statistical analysis used. The concepts below are general explanations; they do not claim that a particular method was used in this study.

What does a mean describe?

In general, a mean gives a central summary of the observed values in a group. It can be useful for describing the average BMI z-score at a measurement time or the average change when change is defined for each participant. A mean alone does not show how much individual participants’ values differ from one another. It also does not show how precisely the mean has been estimated. The registry record does not report the mean values for baseline or 6 months.

What does standard deviation describe?

In general, standard deviation describes the spread of individual measurements around their mean. A larger spread means participant values are more dispersed; a smaller spread means they are more clustered. Standard deviation is not the same as the uncertainty of the mean. The registry lists standard deviation as the dispersion measure, but does not report its values. It is therefore not possible to assess the observed variability from the registry record.

How would a change estimate be interpreted?

In general, a within-person change is calculated by comparing each participant’s measurement at one time with that participant’s measurement at another time. An average of those individual changes describes the mean change among participants included in that analysis. The registry’s stated direction convention is that a negative BMI z-score change indicates a decrease in BMI, while a positive change indicates an increase. The record does not report a change estimate or specify the analysis used to obtain one. It therefore cannot be assumed that a particular change-score method was used.

What does a confidence interval add?

In general, a confidence interval describes the precision of an estimate under the assumptions of the statistical method. A narrow interval indicates greater precision than a wide interval, while an interval that spans a range of plausible values signals uncertainty about the exact magnitude. An interval is not a guarantee that the true value lies within its limits. No confidence interval for the primary outcome is reported in the registry record, so the precision of any BMI z-score change cannot be evaluated.

Why does the single-group design matter?

In general, measurements from the same participants over time can describe a temporal pattern. Without a comparison group, however, the pattern does not isolate the effect of the intervention. Changes could coincide with other influences, including changes in circumstances or behavior over time. A randomized comparison can help address some alternative explanations by comparing groups formed through random allocation; this record describes neither random allocation nor a comparator. The design therefore supports a different kind of interpretation from a controlled trial.

What is over-dispersion?

In general, over-dispersion occurs when observed variability is greater than a statistical model assumes. It matters because a model that understates variability can make uncertainty appear smaller than it is. This concept is particularly relevant to some count-data models; it is not evidence that over-dispersion occurred in this study. The primary endpoint is described as a continuous measure, and the registry record does not report a model or a dispersion assessment.

How should planning illustrations be read?

The registry describes sample-size illustrations as planning calculations based on the observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The stated effect to detect is a fraction of the observed effect. These are planning assumptions, not evidence that the trial used a two-arm design: the registered study is single group. In general, a planning calculation estimates the sample size that might be needed under stated assumptions. It is not a measure of what the completed study achieved, and it is not observed power. The registry record does not report a study-specific sample-size justification or a registered analysis plan.

Because the primary outcome estimates and registered analyses are not reported, these statistical concepts provide context for interpreting the endpoint rather than a reconstruction of the study’s results. The registry record does not identify a test, model, adjustment strategy, or method for handling repeated measurements.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("W8Loss2Go App")
n   <- c(18)
m   <- c(-0.1)
sp  <- c(0.04)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  W8Loss2Go App  18  -0.100  0.040  -0.120  -0.080

11. Multiplicity, Missing Data and Analysis Populations

The registry lists four outcome measures: the primary BMI z-score and secondary outcomes concerning withdrawal from problem foods, elimination of daytime snacking, and reduction of daily meal portion size using a wireless food scale. When a study evaluates several outcomes, general statistical practice considers how to interpret the chance of at least one apparently notable result across those outcomes. Adjustment or a clearly defined hierarchy can be used in some analyses, but neither approach can be assumed. A multiplicity strategy is not reported in the registry record.

The registry identifies the primary outcome population as 18 youth who completed the app intervention. It does not report whether all participants had baseline and 6-month BMI z-scores, how missing measurements were handled, or whether any analysis used a different population. The number of participants included in each secondary outcome analysis is also not reported in the registry record. The listed enrollment and completer description do not establish the completeness of outcome data.

In general, missing outcome data can affect both the precision and interpretation of an estimate, particularly when the likelihood of missingness is related to participants’ outcomes or experiences. Analysts may use different approaches to address missingness, but the method and assumptions should be reported to judge their effect. No missing-data method, analysis population definition beyond the primary population description, or sensitivity analysis is reported in the registry record.

The registry lists zero analyses. It does not report an analysis plan, interim analyses, or methods for addressing multiple outcomes. Without those details and the outcome results, the record does not support conclusions about how multiplicity or missing data influenced the findings.

12. 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.

The registry’s serious adverse event figures for the W8Loss2Go App group list 18 participants at risk and zero participants affected. The death count is also zero. These are the posted counts for the serious adverse event fields, not a complete description of every possible safety outcome or experience.

The group also lists 18 participants at risk and zero affected in the other adverse event fields. The registry does not list any top serious event terms. These figures should be read as counts recorded in this registry entry. They do not show that every kind of adverse event was assessed, nor do they establish that no event could occur outside the recorded categories or reporting period.

In general, a zero count in a study group is not proof that an event is impossible or that risk is absent. The ability to characterize uncommon events depends on the amount and duration of observation and on how events were collected and reported. The registry record does not report additional details about event definitions, collection procedures, follow-up duration for safety, or severity beyond the serious adverse event listing. The figures therefore describe the recorded counts without establishing broader safety conclusions.

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

The registry record describes a completed, single-group study of the W8Loss2Go app intervention among youth with obesity. It specifies BMI z-score at baseline and 6 months as the primary endpoint and gives the direction used to interpret change. It also names secondary outcomes related to problem foods, daytime snacking, and meal portions. The primary outcome population is described as 18 youth who completed the app intervention.

Those details establish what the study was intended to assess, but the registry record does not report the primary endpoint values, change estimate, or uncertainty interval. It does not report the secondary outcome results. The record therefore does not show whether BMI z-score changed, how large any change was, or how precisely it was estimated. It also does not state how many participants contributed data to each outcome analysis.

The study has no registered comparator group and no randomized allocation. In general, a before-and-after pattern in one group cannot by itself establish that an intervention caused the pattern. Other changes over time may also contribute. The registry record does not provide a controlled estimate that would distinguish the intervention from those possibilities.

The listed serious adverse event counts are zero affected participants among 18 at risk, with zero deaths recorded. Those figures describe the registry entry and should not be interpreted as proof that the intervention carries no risk. The record does not report details that would support a broader assessment of safety.

Overall, the registry record identifies the intervention, intended population, endpoint, and some safety counts, but does not report the efficacy results or analyses. It cannot support a conclusion about the magnitude, precision, or cause of an outcome change.

14. Why This Trial Matters Statistically

This study is statistically informative as an example of why an outcome definition and an outcome result are different kinds of information. The registry describes BMI z-score, the measurement times, the primary outcome population, and the direction of change. Those details clarify what was intended to be measured. They do not tell the reader what values were observed or how uncertain any change may be.

The single-group design also highlights the distinction between describing change and estimating a comparative intervention effect. In general, repeated measurements can show whether values differ over time among participants with measurements. A comparator is needed for a direct comparison with another care condition, and random allocation can strengthen the interpretation of such a comparison. This registry entry describes neither random allocation nor a comparator, so a causal contrast is not available.

Another statistical issue is transparency about analysis populations and missing data. The primary population is described as 18 youth who completed the intervention, but the record does not state how many had measurements available at both time points or how missing outcomes were handled. Those details matter because the analyzed participants may not represent everyone who began a study.

The record lists several outcomes but does not report their results or a multiplicity approach. In general, when several outcomes are considered, readers need to know which analysis was primary and how other findings were interpreted. Finally, the registry includes sample-size planning assumptions, but those planning illustrations are not evidence of observed power or trial efficacy. Together, these points show why numerical results, uncertainty, and analysis methods are needed alongside a registered question to assess what a study found.

15. 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 central limitation for interpreting the registered study is that outcome estimates are not reported in the registry record. The primary BMI z-score means, standard deviations, change estimate, and uncertainty interval are absent. Results for the listed secondary outcomes are also not reported. The number of registered analyses is zero, and the statistical analysis plan is not reported in the registry record.

The design is single group, with no randomized allocation or comparator. As a result, the registry record does not provide a direct comparison against another intervention or care condition. Any change over time, if present, could not be separated from other influences using a controlled contrast described in this record.

The record identifies 18 youth who completed the app intervention as the primary outcome population, but it does not report details about recruitment, participant characteristics, eligibility criteria, or the number with measurements available at each time point. It does not describe missing-data handling, the analysis population for secondary outcomes, or sensitivity analyses. These omissions limit assessment of representativeness and robustness.

The endpoint description explains the direction of BMI z-score change, but the registry record does not report the reference details or a threshold for a clinically meaningful change. It also does not report the methods used to analyze repeated measurements, address multiple outcomes, or estimate uncertainty. The serious adverse event counts are listed, but broader event definitions and collection details are not reported. These limitations concern what can be established from the registry record; they do not establish that unreported procedures or analyses were absent from other records.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: W8Loss2Go: mHealth Weight Management Strategy — NCT02689154.
• Registry record last updated 2019-04-12; status last verified 2019-04.
• Results first posted 2019-04-12.
• 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.

19. Record Summary

The registry lists NCT02689154 as W8Loss2Go: mHealth Weight Management Strategy, a completed, single-group intervention study sponsored by Children’s Hospital Los Angeles. The intervention was the W8Loss2Go app, and enrollment was 18. The study start is listed as 2016-04, with primary completion in 2017-09.

The primary endpoint was BMI z-score at baseline and 6 months among 18 youth who completed the app intervention. Listed secondary outcomes concerned withdrawing from problem foods, eliminating daytime snacking, and reducing meal portion size using a wireless food scale. The record lists four outcome measures and zero analyses.

The registry reports zero participants affected by serious adverse events among 18 at risk and zero deaths. It does not report the primary or secondary outcome results, statistical analysis methods, missing-data methods, or a comparator-based estimate.