Arthritis Pilot for Preserving Muscle While Losing Weight: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Arthritis Pilot for Preserving Muscle While Losing Weight (NCT02239939), a randomized na study. The primary outcome is Change in Lean Mass Measured by DXA.

2. Clinical Question

3. Trial Design

The registry identifies NCT02239939 as a randomized, single-masked, parallel-group study. It lists the phase as NA and the status as completed. Wake Forest University Health Sciences is the sponsor. The record lists 37 participants enrolled, with a start date of 2014-10 and primary completion in 2016-01.

The two groups both received a dietary weight-loss intervention lasting 22 weeks. The Vest + Diet group was additionally asked to wear a weighted vest for >10 hours a day, with vest weight adjusted to match weight lost. The No Vest + Diet group was asked to maintain daily habits other than following the diet protocol. The contrast therefore concerns adding vest use to the shared diet intervention, rather than comparing weight loss with no weight-loss intervention.

The record labels the trial single-masked but does not report who was masked or how masking was maintained. The specific randomization procedure, allocation concealment, eligibility criteria, recruitment setting, and adherence measures are not reported in the registry record. The total enrollment is not the same as the number contributing to the posted primary-outcome summaries: those summaries list 18 participants for Vest + Diet and 15 for No Vest + Diet. The reasons for this difference and the analysis population definition are not reported in the registry record.

The primary outcome was change in lean mass measured by DXA at baseline and 22 weeks. Hip bone density and self-reported fatigue are named among the secondary outcomes. The posted record includes numerical results for fatigue but does not include numerical hip bone-density results. A complete original protocol or a detailed statistical analysis plan is not reported in the registry record.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

Reasons for not completing this period:

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Change in Lean Mass Measured by DXA, measured over Baseline and 22 weeks.

The primary endpoint is change in lean mass measured by DXA from baseline to 22 weeks. Lean body mass is described as a whole-body measure that includes lower-extremity lean mass in its total calculation. The outcome is reported as a mean change in kilograms, with a standard deviation for each group.

Lean mass was selected to address the concern that weight loss may involve loss of lean tissue as well as loss of body weight. The registry’s study summary asks whether wearing a weighted vest during active weight loss is associated with less loss of lean mass. This makes lean-mass change relevant to the stated study question, but it does not make the endpoint a direct measure of muscle strength, physical function, or overall health. Those are distinct outcomes.

The endpoint is a change score: a negative group mean indicates that the measured quantity decreased on average between baseline and follow-up, while a positive mean difference between groups describes the contrast in their average changes. The posted group means are both negative. The registry record does not provide the individual participant measurements, the distribution of changes, or a detailed account of how DXA measurements were collected and processed. Those details limit how fully the measurement quality and analysis can be assessed.

7. Results Posted in the Registry

• No Vest+Diet: mean -2.30 versus -2.90 on control; difference 0.60 (95% CI -0.61 to 1.81), standardized effect d = 0.34; z-test p = 0.332.

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.

Changes in Self-report on Fatigue Using Pittsburgh Fatigability Scale (PFS)

• 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 deviations.
• Result:
  • No Vest + Diet: mean 12.30 versus 15.30 on control; difference -3.00 (95% CI -12.70 to 6.70), standardized effect d = -0.21; z-test p = 0.544.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between No Vest + Diet and the control. The interval gives the range of effects that remain compatible with the data.

The secondary outcomes are intended to broaden the clinical picture beyond lean-mass change. Hip bone density is named as an outcome, and self-reported fatigue using the Pittsburgh Fatigability Scale is also listed. Numerical results are posted for fatigue, whereas numerical hip bone-density results are not reported in the registry record.

The available secondary comparison is an unadjusted mean comparison. Its estimate is uncertain, with a confidence interval spanning values on both sides of zero. The registry does not provide enough information about the scale’s interpretation to label the direction of the change as improvement or worsening. The primary and secondary outcomes address different constructs, so a fatigue result cannot substitute for evidence about lean mass, bone density, physical function, pain, or quality of life.

Across the outcomes with numerical results, the record does not establish a consistent pattern of benefit across the broader set of outcomes described in the study summary. Several intended outcomes, including physical function, self-reported disability, pain, stiffness, quality of life, and weight loss, do not have numerical results in the posted material described by the registry record. The absence of reported values should not be interpreted as a finding of no difference.

Secondary analyses generally carry less confirmatory weight when many outcomes are examined, because multiple opportunities for an apparently notable result can arise by chance. The registry record does not report a multiplicity adjustment or a hierarchy for interpreting secondary outcomes. The fatigue comparison should therefore be understood as exploratory evidence that can inform further research, not as a stand-alone basis for a definitive conclusion about the vest intervention.

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

• Change in Hip Bone Density
• Changes in Self-report on Fatigue Using Pittsburgh Fatigability Scale (PFS)

9. Statistical Interpretation

10. Statistical Methods Explained

The primary outcome is continuous: each participant has a measured change in lean mass, and the registry reports a group mean and standard deviation. A mean summarizes the average change in a group. A standard deviation describes how dispersed individual values are around that group average; it is not the uncertainty in the mean difference itself.

What does the mean difference represent?

The comparison is expressed as No Vest + Diet minus Vest + Diet. With that ordering, the estimate of 0.6 Kg indicates that the average change in the no-vest group was higher than the average change in the vest group. Because both group means are negative, a higher value in this contrast corresponds to a less negative average change in the no-vest group. This is a descriptive direction for the posted estimates, not a conclusion about a causal or clinically important effect.

Random assignment is intended to make treatment groups comparable on average, supporting a comparison of their outcomes. The registry identifies the study as randomized, but the randomization procedure and concealment details are not reported in the registry record. The posted summary comparison is unadjusted. It is not described as an adjusted model controlling for baseline characteristics or other covariates.

How should the confidence interval be understood?

A confidence interval communicates uncertainty around an estimated group difference. In general, intervals that include zero are compatible with no mean difference as well as with effects in either direction, depending on the interval’s limits. The primary interval runs from -0.613 to 1.813 Kg. Thus, the point estimate should not be read as if it were an exact value known for the broader population. The interval is also not a range containing a fixed proportion of individual participants’ changes; it concerns uncertainty in the group comparison.

The registry also posts an unadjusted p-value of 0.332 for the primary comparison. A p-value describes how unusual data at least as inconsistent with a specified null model would be if that model were true, subject to the assumptions of the analysis. It is not the probability that the null hypothesis is true, nor is it a measure of the size or importance of a difference. The record does not report a full statistical analysis plan, including the precise inferential procedure used for the sponsor’s primary analysis.

Why does the pilot size matter?

The primary outcome summary lists 18 participants in one group and 15 in the other. With a limited number of observations, a mean and its uncertainty can be sensitive to the values of individual participants. A wide confidence interval can remain compatible with materially different effects even when the point estimate is modest. This is why a non-significant test in a pilot should not be interpreted as proof that a difference is absent.

The posted planning illustrations use the observed effect as their starting point and show hypothetical participant counts under stated assumptions. Those are design illustrations for a future study, not evidence that the current study had a particular probability of finding an effect. The original trial’s sample-size justification and design assumptions are not reported in the registry record.

What can be concluded about analysis choices?

The registry record supplies group means, standard deviations, an unadjusted comparison, and a confidence interval for the primary outcome. It does not report whether missing outcomes were imputed, how participants were handled after randomization, whether the analysis followed intention-to-treat principles, or whether any transformations or model checks were used. Those omissions mean the posted summaries can be interpreted at the level of the reported group comparison, but do not permit a complete audit of the analysis.

General statistical context: if outcome variability is greater than a model assumes, standard errors and tests based on that model may not describe uncertainty accurately. The registry does not report a diagnostic assessment or an analysis addressing over-dispersion, so no claim about whether it occurred is warranted. More broadly, statistical methods are most interpretable when the outcome definition, analysis population, missing-data rules, and inferential procedure are prespecified and reported. These details are not reported in the registry record.

11. Confidence Intervals and Precision

The primary mean-difference estimate is 0.6 Kg, and its confidence interval extends from -0.613 to 1.813 Kg. The estimate is therefore imprecise: values below and above zero are both compatible with the interval. The interval includes a possibility of a more negative change in the no-vest group and a possibility of a more positive change in that group, relative to the vest group. The data do not pinpoint a narrow range of plausible group differences.

Precision depends on the variability of the outcome and the amount of information available. The posted primary summaries include 18 participants in Vest + Diet and 15 in No Vest + Diet, with standard deviations of 1.6 Kg and 1.9 Kg, respectively. These group summaries help describe the observed data, but do not remove the uncertainty in the estimated difference. The registry does not report a prespecified precision target for the primary comparison.

The unadjusted p-value of 0.332 should be read alongside the estimate and interval, not as a standalone verdict. It does not show that the groups are equal, and it does not distinguish a small effect from a potentially larger effect that the pilot estimates imprecisely. The registry record does not report an equivalence margin that would define what range of differences could count as practically similar.

Confidence intervals are statistical summaries under an analysis model; they do not account automatically for every uncertainty about measurement, missing data, adherence, or generalizability. The record does not provide enough detail to assess those sources fully. The main precision message is that the primary estimate is uncertain, and stronger conclusions would require a better-defined and more precise comparison.

12. Planning a Similar Trial: Sample Size

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

The planning figures are participants per arm, not total events. The posted assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set to a stated fraction of the observed effect. The original trial’s own sample-size assumptions and justification are not reported in the registry record.

For planning at 100% of the observed primary effect, the illustration gives 133 participants per arm for 80% power and 178 participants per arm for 90% power. Planning for 75% of the observed effect gives 236 participants per arm for 80% power and 315 participants per arm for 90% power. Planning for 50% of the observed effect gives 530 participants per arm for 80% power and 709 participants per arm for 90% power.

In plain language, the 80% power column represents a hypothetical design that would have an 80% chance of meeting its statistical criterion if the assumed effect and other planning assumptions were correct. The 90% column describes a design with a higher target chance under those same assumptions. These are planning illustrations, not observed power for this trial.

The pattern follows a general principle: smaller effects are harder to distinguish from random variation, so planning to detect a smaller effect requires more participants. The figures are tied to the observed effect, which may itself be uncertain in a pilot. They should therefore be treated as illustrations rather than as a definitive sample-size recommendation. The accompanying curve represents the same planning relationship; its interpretation depends on the stated assumptions and the effect being targeted.

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 = 0.600; pooled standard deviation σ = 1.742.
2. n = 2 × (1.96 + 0.842)² × 1.742² / 0.600² = 132.3, rounded up to 133 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 <- 0.6                      # observed difference in means
sigma <- 1.74189366735949                     # 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(2239939)
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 = 133 (80% power), 178 (90% power)
 75% of observed effect: n per arm = 236 (80% power), 315 (90% power)
 50% of observed effect: n per arm = 530 (80% power), 709 (90% power)
power.t.test: 133.3 
Simulated power at n = 133 per arm: 0.800 (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 lists multiple outcomes, including change in lean mass, hip bone density, and fatigue, while the study summary also refers to physical function, disability, pain, stiffness, and quality of life. When several outcomes or comparisons are examined, the chance of obtaining at least one apparently unusual result can increase. Statistical methods for addressing this issue may include prespecifying a primary outcome hierarchy or adjusting inference across a defined family of tests. Whether any such approach was used is not reported in the registry record.

The posted primary comparison has an unadjusted p-value, and the fatigue comparison is also unadjusted. The record does not report a multiplicity strategy, a prespecified order for secondary outcomes, or a statistical analysis plan identifying which comparisons were confirmatory. As a result, the primary outcome is the clearest stated focus, while secondary findings require cautious interpretation. No claim should be made that the set of outcomes was protected against multiple testing.

Missing-data handling is also not reported in the registry record. The primary outcome summaries list 18 participants in Vest + Diet and 15 in No Vest + Diet, while total enrollment is listed as 37. The record does not explain why the numbers contributing to the outcome summaries differ from total enrollment, whether any participants lacked measurements, or how missing measurements were handled. No missing-data method, sensitivity analysis, or participant flow account is reported in the information available.

The analysis population is not defined in the registry record. It is therefore not possible to determine from the posted summaries whether results include all randomized participants, only participants with observed follow-up data, or another population. The record also does not state whether adherence, protocol deviations, or withdrawal affected inclusion in the analysis. These omissions matter because analysis choices can affect the estimated comparison, particularly in a small trial. They limit the ability to assess robustness, but they do not by themselves show that the posted results are biased.

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: dehydration (5.9%), bronchitis (5.9%), diverticulitis (5.0%), chest pain (5.0%).

The registry reports serious adverse events for the Vest + Diet group as 2 affected participants among 20 at risk, and for the No Vest + Diet group as 2 among 17 at risk. It reports zero deaths in each group. These are counts within the record’s stated at-risk groups; they are not the primary efficacy outcome and should be read separately from the mean changes in lean mass.

The record also lists other adverse events affecting 15 of 20 at risk in Vest + Diet and 10 of 17 at risk in No Vest + Diet. The listed serious-event terms include dehydration and bronchitis, each reported as 5.9%, and diverticulitis and chest pain, each reported as 5.0%. The registry does not provide enough detail to determine how these term percentages were calculated or whether events were judged related to an intervention.

These figures describe reported events in this pilot; they do not establish a comparative safety profile. The group sizes are limited, and the registry record does not report event timing, severity detail, attribution procedures, or a formal between-group safety analysis. Counts should not be interpreted as proof that an event was caused by vest use or by the diet intervention.

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

The posted primary result is an estimate of the difference in average lean-mass change between two groups receiving dietary weight loss, one with an added weighted-vest regimen and one without it. The point estimate favors a less negative change in the no-vest group, but its confidence interval includes zero and extends in both directions. The result is therefore uncertain rather than a precise demonstration of a difference or of equivalence.

The study’s stated hypothesis also concerns similar weight loss and less loss of bone density with vest use. The primary endpoint does not directly test all of those claims. Numerical results for weight loss and hip bone density are not reported in the registry record. The listed fatigue result is a separate secondary outcome, and the record does not report numerical findings for several other outcomes mentioned in the study summary. The primary comparison cannot answer questions about these unreported outcomes.

More generally, a mean change in lean mass is not interchangeable with muscle strength, physical function, pain, disability, quality of life, or long-term outcomes. The registry record does not report enough information to assess whether any measured difference would be clinically important. It also does not report an equivalence margin or a prespecified threshold for a meaningful change.

The completed pilot contributes a randomized comparison and outcome summaries, but its limited outcome-group counts and imprecise estimate constrain the strength of inference. A non-significant result does not prove the interventions are the same; a numerical difference does not establish that an intervention caused a meaningful benefit. The appropriate reading is narrow: the posted data estimate a difference in lean-mass change over the specified follow-up, with substantial uncertainty and important outcomes left unreported.

17. Why This Trial Matters Statistically

This trial matters statistically because it illustrates the distinction between an estimated effect and the certainty of that estimate. The primary result has a numerical point estimate, but the confidence interval spans zero. Reporting both helps prevent a p-value alone from being mistaken for evidence that no difference exists. The interval makes clear that the pilot does not tightly resolve the direction or size of the group contrast.

It also illustrates why a randomized pilot and a definitive efficacy study serve different purposes. A pilot can provide observed outcome variability and an initial estimate that may inform later planning. But a planning calculation based on an observed pilot effect is sensitive to uncertainty in that estimate. The resulting participant counts are illustrations under explicit assumptions, not proof that the original design was adequately powered or that a later study should adopt those counts without further justification.

The comparison also highlights the importance of reporting analysis details. Readers need to know which participants were included, how missing outcomes were handled, and whether secondary testing was controlled or interpreted in a prespecified hierarchy. Those details are not reported in the registry record. Their absence limits reproducibility and makes it harder to judge the robustness of the posted comparisons.

Finally, this study distinguishes an intervention’s rationale from the endpoints actually reported. The registry summary describes possible effects on muscle, bone, function, and symptoms, but the available numerical primary result addresses lean mass and the posted secondary comparison addresses fatigue. A careful statistical reading keeps each inference tied to its measured outcome and does not extend it to unreported outcomes.

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 comparison is based on outcome summaries for 18 participants in Vest + Diet and 15 in No Vest + Diet. The registry lists total enrollment of 37 but does not explain the difference between enrollment and the numbers in these summaries. The analysis population, participant flow, and reasons for any missing outcome data are not reported in the registry record.

The primary confidence interval is broad enough to include effects in either direction. This limits the ability to distinguish an absent effect from a potentially relevant difference that the pilot estimates imprecisely. The record does not report a clinical threshold for meaningful lean-mass change or an equivalence margin.

Protocol and analysis details are sparse in the registry record. Eligibility criteria, randomization implementation, allocation concealment, identity of the masked party, adherence, DXA measurement procedures, missing-data methods, and the original sample-size justification are not reported. The statistical plan for secondary outcomes and multiplicity is also not reported.

Several outcomes described in the study summary do not have numerical results in the posted information. Hip bone-density values and results for weight loss, physical function, disability, pain, stiffness, and quality of life are not reported in the registry record. Consequently, the available results cannot provide a complete account of the broader study aims.

Finally, the registry identifies a completed pilot and reports an unadjusted comparison. The summaries alone do not establish clinical importance, generalizability to a particular age group, or the durability of any change beyond the stated 22-week outcome timeframe. These limitations call for restraint in interpreting the estimate, not an assumption that the result is invalid.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Arthritis Pilot for Preserving Muscle While Losing Weight — NCT02239939.
• Registry record last updated 2018-03-09; status last verified 2018-02.
• Results first posted 2018-01-29.
• 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

NCT02239939 is a completed randomized, single-masked, parallel-group pilot sponsored by Wake Forest University Health Sciences. The registry lists enrollment of 37 and compares a 22-week dietary weight-loss intervention with the same diet intervention plus weighted-vest use.

The primary outcome is mean change in DXA-measured lean mass from baseline to 22 weeks. The posted group means are negative in both arms, and the unadjusted mean difference is 0.6 Kg, with a confidence interval from -0.613 to 1.813. The interval includes zero, leaving the estimated group difference uncertain.

Fatigue is reported as a secondary outcome. Numerical results for hip bone density and several outcomes named in the study summary are not reported in the registry record. Important details about the analysis population, missing data, multiplicity, and original design assumptions are also not reported.