Role of the Gut Microbiome on Lean Mass and Physical Function in Older Adults: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Role of the Gut Microbiome on Lean Mass and Physical Function in Older Adults (NCT02811445), a registered phase not stated study. The primary outcome is Percentage of Whole Body Lean Mass (%WBLM).

2. Clinical Question

3. Trial Design

The registry record describes a study of gut bacteria, serum metabolites, lean mass, and physical function in older adults. Its stated rationale is that prior work had reported associations between circulating gut bacteria-related metabolites and measures of lean or skeletal muscle mass and physical function, while studies identifying associations between gut bacteria themselves and those outcomes had not yet been reported. The proposed study was intended to investigate those relationships and inform future research.

The record lists two physical-function groups: High Functioning, defined by an SPPB score greater than or equal to 11, and Low Functioning, defined by an SPPB score less than or equal to 7. It explicitly notes that this is not a randomized comparison, that allocation is not stated, and that the arms are not a like-for-like control comparison. These labels describe function categories; they do not establish that one group received an intervention and the other served as a treatment control.

The registry lists an enrollment of 29, a start date of 2016-05, a primary completion date of 2018-02, and a status of COMPLETED. The primary outcome is a continuous measure, reported as a mean with standard deviation, at a 1 month timeframe. Four outcome measures are listed in total, but the additional outcome details are not reported in the registry record. No statistical analyses are listed.

The record does not report how participants were recruited, how measurements were timed relative to one another, whether any intervention was administered, or how participants were assigned to groups. Those details should not be inferred from the group names or study rationale.

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: Exclusion criteria included a SPPB score of 9 or 10, a BMI ≥ 35 kg/m2, acute or terminal illness, myocardial infarction in the past 6 months, unstable cardiovascular disease, MMSE score \< 23, blood pressure \> 150/90 mm Hg, androgen therapy in males, estrogen therapy in females, and others.

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 Percentage of Whole Body Lean Mass (%WBLM), measured over 1 month.

The primary endpoint is percentage of whole-body lean mass (%WBLM), expressed as a percentage of whole-body mass. The record says it is measured with dual x-ray absorptiometry (DXA) at the 1 month timeframe. It identifies the summary measure as a mean and the dispersion measure as a standard deviation. The endpoint description states that a higher %WBLM indicates a higher amount of whole-body lean mass compared with lower values.

As a continuous measure, %WBLM can describe variation in lean mass across participants rather than placing them only into categories. In general, reporting a mean describes the group’s average value, while a standard deviation describes how dispersed individual values are around that average. Neither quantity alone establishes a relationship with physical function or gut bacteria; that requires an analysis connecting measurements across participants or groups.

The registry record does not report the observed mean or standard deviation for either function group, nor does it report a difference, association, confidence interval, or test result for this endpoint. The purpose of the endpoint can be described, but the posted record does not provide the numerical outcome needed to assess its observed pattern.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What kind of outcome is reported? The primary measure, %WBLM, is continuous: it can take a range of values rather than only a category. The registry identifies the planned summary as a mean and the accompanying dispersion as a standard deviation. In general, a mean gives a group’s average, while a standard deviation describes the spread of individual measurements around that average. The record does not post the actual means or standard deviations, so neither the average level nor variability can be assessed.

What would an estimate and confidence interval contribute? In general, an effect estimate expresses the size and direction of a contrast or association in the units relevant to the outcome. A confidence interval gives a range of values compatible with the data and the statistical method used; it helps readers judge precision as well as direction. A narrow interval indicates greater precision than a wide one, though interpretation also depends on the question and the estimate’s scale. No estimate or confidence interval for %WBLM is reported in the registry record. It is therefore not possible to assess the size or precision of a primary-outcome relationship.

What does a significance test tell readers? In general, a p-value describes how incompatible the observed data are with a specified null model, under the assumptions of the test. It does not measure the probability that the null hypothesis is true, nor does it measure the clinical importance of an effect. The registry record lists no analyses and reports no p-value. No statistical significance claim can be evaluated from the posted record.

How should the group contrast be understood? High Functioning and Low Functioning are categories defined by SPPB score. The record states that the comparison is not randomized, allocation is not stated, and the arms are not a like-for-like control comparison. In general, categorizing participants by an existing characteristic can describe differences between those categories, but the contrast can reflect other differences between the groups as well. Without a reported analysis and information about adjustment for other characteristics, a group contrast would not by itself establish a causal effect. The registry record does not report any adjusted or unadjusted group estimate.

What is over-dispersion, and is it relevant? In general, over-dispersion means that variability in data is greater than a chosen statistical model expects. It matters when a model’s uncertainty estimates rely on a variance assumption that does not fit the data; ignoring extra variability can make standard errors too small and confidence intervals too narrow. This concept is most relevant to outcomes and models with particular distributional assumptions, such as count outcomes. The primary outcome is described as a continuous measure summarized by a mean and standard deviation. The registry record does not report a model, diagnostics, or an over-dispersion assessment, so there is no basis to say that over-dispersion was tested or affected the analysis.

How should the sample-size illustration be read? The stated assumptions describe a planning illustration calculated from an observed effect, not the study’s original design justification. The assumptions include a two-sided significance level of 0.05, equal allocation between the two arms, a normal approximation, and a target effect expressed as a fraction of the observed effect. In general, planning calculations estimate the number of participants needed under specified assumptions to detect a target effect at a chosen significance level. They do not show that a study had a particular probability of detecting an effect after it was conducted. Such a post hoc calculation is not observed power. The record does not report numerical planning results or the observed effect value. The original sample-size justification is not reported in the registry record.

What does the analysis record establish? The registry lists four outcome measures and no analyses. That supports a narrow statement: analysis results are not posted in the registry record. It does not establish why results are absent, whether analyses were conducted outside the registry, or what those analyses might have shown. The statistical analysis plan, model specification, covariate selection, handling of repeated measurements, and any interim analyses are not reported in the registry record. They should not be inferred from the endpoint summary or the study’s stated hypothesis.

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("High Functioning", "Low Functioning")
n   <- c(18, 11)
m   <- c(67.3, 61.9)
sp  <- c(6.77, 6.64)
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  High Functioning  18  67.300  6.770  63.933  70.667
CARM  Low Functioning  11  61.900  6.640  57.439  66.361

11. Multiplicity, Missing Data and Analysis Populations

The registry lists four outcome measures, while the number of analyses listed is zero. The primary outcome is identified as %WBLM; details for the other outcome measures are not reported in the registry record. The record does not explain whether outcomes were organized into primary and secondary families for statistical testing, whether any multiplicity adjustment was planned, or how multiple comparisons were handled. With several outcomes or contrasts, repeated testing can increase the chance of at least one apparently notable result by chance. In general, a prespecified testing strategy or adjustment can help readers understand how that issue was addressed. No such strategy is reported.

Missing-data handling is not reported in the registry record. There is no information about the amount or pattern of missing primary outcome measurements, exclusions, imputation, or sensitivity analyses. The analysis population is also not reported: the record does not say which participants were included in any outcome analysis or whether all enrolled participants contributed measurements.

The record lists an enrollment of 29, but that figure alone does not establish the number with complete endpoint data or the number included in an analysis. No statistical analyses are posted, so there is no reported analysis population against which to assess completeness. The original statistical plan, including any rules for handling missing measurements or multiple comparisons, is not reported in the registry record.

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 serious adverse-event entries are grouped by the two SPPB-defined categories. For High Functioning, 18 are listed as at risk, with 0 serious adverse events, 0 other adverse events, and 0 deaths. For Low Functioning, 11 are listed as at risk, with 0 serious adverse events, 0 other adverse events, and 0 deaths. The registry record lists no top serious-event terms.

These are safety counts in the registry, not results for the primary %WBLM endpoint. In general, a zero event count means that no events of that category were recorded in the listed group in the registry entry; it does not prove that the underlying risk is absent. The record does not report additional details about how adverse events were defined, collected, or monitored, or the time at risk for these entries. Because the groups are function categories rather than randomized treatment and control groups, the entries should not be interpreted as a comparative estimate of treatment safety.

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

The registry record establishes that the study focused on gut bacteria, serum metabolites, lean mass, and physical function in older adults. It defines High Functioning and Low Functioning groups by SPPB score and identifies %WBLM measured by DXA as the primary endpoint at the 1 month timeframe. It also records safety counts for those groups.

The record does not establish whether %WBLM differed between the groups, whether it was associated with gut bacteria or serum metabolites, or how precise any such relationship was. The primary outcome’s observed values and statistical analyses are not reported in the registry record. The study’s rationale and hypotheses are not results, and the existence of an endpoint does not establish that the expected relationship was observed.

Even if a group contrast were available, the record describes a non-randomized comparison and says allocation is not stated and the arms are not a like-for-like control comparison. In general, observed differences between function categories can be associated with characteristics other than the categories themselves. A group contrast would not by itself establish causation or show that changing gut bacteria would change lean mass or physical function.

The safety entries report zero recorded serious adverse events, other adverse events, and deaths in both listed groups. Those entries describe what is recorded, not proof that no risk exists, and they do not answer the primary research question.

The record’s stated aim is to provide a basis for future studies of targeted modulation of gut microflora. That is an intended research direction, not evidence from this registry entry that such modulation is effective. The posted information supports a description of the study question and its planned primary measure, but not a conclusion about the presence, size, direction, or cause of an outcome relationship.

14. Why This Trial Matters Statistically

This study is statistically interesting because it connects measures from different domains: physical function, body composition, gut bacteria, and serum metabolites. The registry’s hypothesis concerns possible relationships among those measures in older adults. Translating that broad hypothesis into interpretable evidence requires clear measurement definitions and analyses that distinguish description, association, and causation.

The primary endpoint is defined as %WBLM measured using DXA, with a mean and standard deviation as the planned summary. The function groups are also defined using explicit SPPB thresholds. These details give readers a framework for understanding what was intended to be measured and how the groups were characterized. At the same time, the registry explicitly cautions that the groups are not a randomized, like-for-like control comparison. That distinction is central to statistical interpretation: a difference between categories would describe an association unless a stronger design and analysis supported a causal interpretation.

The record also illustrates why registration details and posted results serve different purposes. It reports the rationale, endpoint, timeframe, group definitions, enrollment, and safety entries, but lists no statistical analyses and gives no primary outcome values. Without estimates and measures of uncertainty, readers cannot assess magnitude, direction, or precision. A research question can be scientifically motivated without the registry entry documenting evidence that answers it.

The stated planning assumptions further highlight that sample-size calculations depend on assumptions about the target effect, allocation, significance level, and statistical approximation. Such illustrations are planning tools; they do not substitute for observed results or the original design justification. The numerical planning results and original justification are not reported in the registry record.

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 principal limitation for interpreting this record is that it contains no posted primary outcome values or statistical analyses. The mean and standard deviation for %WBLM are not reported, and neither are an effect estimate, confidence interval, or p-value. As a result, the record cannot establish the direction, size, or precision of any relationship between physical-function category and lean mass.

The comparison is non-randomized, allocation is not stated, and the record says the groups are not a like-for-like control comparison. The group labels are based on SPPB thresholds, so they should not be treated as intervention assignments. The registry record does not report methods for controlling potential differences between groups, and no adjusted analysis is listed.

Other details needed to evaluate the evidence are not reported in the registry record, including participant characteristics, recruitment methods, endpoint completeness, missing-data handling, analysis populations, covariate selection, and the statistical analysis plan. Although four outcome measures are listed, details for outcomes beyond the primary measure are not reported; multiplicity handling is also not reported.

The record lists an enrollment of 29, but that does not establish how many participants had complete primary endpoint data or were included in an analysis. The safety counts do not resolve this limitation because they concern adverse-event recording, not the primary endpoint. The registry record also does not provide numerical sample-size illustrations or the original sample-size justification.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Role of the Gut Microbiome on Lean Mass and Physical Function in Older Adults — NCT02811445.
• Registry record last updated 2020-08-06; status last verified 2020-07.
• Results first posted 2020-08-06.
• 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 record describes a completed study of gut bacteria, serum metabolites, lean mass, and physical function in older adults with a listed enrollment of 29. It defines High Functioning by an SPPB score greater than or equal to 11 and Low Functioning by a score less than or equal to 7. The record states that this is not a randomized comparison, allocation is not stated, and the arms are not a like-for-like control comparison.

The primary endpoint is %WBLM measured by DXA at the 1 month timeframe, summarized as a mean with standard deviation. The registry lists four outcome measures and no statistical analyses. Primary outcome values and inferential results are not reported in the registry record. The safety entries record zero serious adverse events, zero other adverse events, and zero deaths for each group. These details describe the registered study and its posted entries, but do not establish an outcome relationship or causal effect.