This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Metabolic Parameters 3 Months, 9 Months, and 2 Years After Bariatric Surgery (NCT00178633), a registered phase not stated study. The primary outcome is Change in Weight.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00178633 |
| Phase | Phase not stated |
| Condition | Obesity, Diabetes, Heart Failure |
| Allocation | Not Stated |
| Design model | Not Stated |
| Masking | Not Stated |
| Enrollment | 43 |
| Arms in the primary outcome | n/a |
| Lead sponsor | The University of Texas Health Science Center, Houston |
| Results posted | Yes |
2. Clinical Question
Population
Patients undergoing bariatric surgery who agreed to research assessment and follow-up. The registry lists obesity, diabetes, heart failure, and insulin resistance among the conditions of interest; it does not say that every participant had each condition.
Intervention
Bariatric surgery. Participants were already undergoing clinical procedures; the procedures were not assigned as part of the research trial. The registry says patients had one of two procedure types, without separating outcome analyses by type.
Comparator
No randomized control group is described. The study follows outcomes over time after surgery, so the main comparison is between measurements at different follow-up times rather than between surgery and an assigned control treatment.
Primary question
What was the mean change in weight from baseline to 9 months after surgery? The endpoint description says negative values represent weight loss and that the change is broken out into 0-3months and 3-9months. The numerical estimates are not reported in the registry record.
The broader research purpose appears to include changes in metabolic profile and cardiac measures over time. The registry lists changes in glucose, tissue Doppler diastolic velocity, and left ventricular mass as secondary outcomes. It also describes assessments of anthropometrics, metabolic profile, skeletal muscle biopsy, and echocardiogram at baseline, 3 months, and 9 months after surgery. These assessments provide context for the research question, but their numerical results are not reported in the registry record.
The follow-up description includes an assessment at 2 years, although the primary endpoint is specified for 0 to 9 months. The distinction matters: a longer follow-up period does not change the stated primary time frame, and participation at the later time point was incomplete. The question is therefore about a mean within-cohort change, not a randomized estimate of the effect of surgery relative to no surgery or another treatment.
3. Trial Design
This completed study enrolled 43 participants, according to the registry record. Its stated purpose was to assess changes after bariatric surgery, including anthropometric, metabolic, muscle-biopsy, and echocardiographic measures. Participants were already undergoing clinical bariatric procedures; the research involved analysis and follow-up rather than assignment to surgery. The registry does not describe a randomized comparison or a control group, and allocation is not stated.
The record identifies bariatric surgery as the intervention and says participants underwent one of two types of procedure. Outcome analyses did not distinguish between those types. As a result, the recorded follow-up describes a cohort exposed to surgery rather than a comparison designed to isolate differences between procedure types.
Assessments are described at baseline, 3 months, and 9 months after surgery, with 2-year assessments also mentioned. The summary says all 43 participants reportedly completed the 3- and 9-month evaluations. It also says only 15 completed the 24-month evaluations, because 28 were unwilling to return. Those later follow-up figures indicate that the observed cohort at 2 years was smaller than at earlier visits. The registry does not report how the 2-year results were analyzed or whether participants with incomplete follow-up differed from those who returned.
The primary outcome is change in weight, expressed as a mean with a 95% confidence interval and specified for 0 to 9 months. The endpoint description also separates change into 0-3months and 3-9months. The registry lists four outcome measures and one analysis, but detailed analysis methods are not reported in the registry record. The start date is 2004-05, the primary completion date is 2008-08, and the status is COMPLETED. The sponsor is The University of Texas Health Science Center, Houston.
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
| Stage | Bariatric Surgery |
|---|---|
| STARTED | 43 |
| COMPLETED | 37 |
| NOT COMPLETED | 6 |
Reasons for not completing this period:
| Reason | Bariatric Surgery |
|---|---|
| Lost to Follow-up | 6 |
Analysis population for the primary outcome, as defined in the registry: broken out into 0-3months and 3-9months below
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: 43 patients were originally enrolled, and 37 participated through 9 months; 15 female participants returned for an additional 2 year analysis.
| Characteristic | Unit | Bariatric Surgery |
|---|---|---|
| Participants analysed | 43 | |
| Age, Continuous | years | 45 (SD 1.6) |
| Sex: Female, Male: Female | Participants | 37 |
| Sex: Female, Male: Male | Participants | 6 |
| Region of Enrollment: United States | participants | 43 |
6. Primary Endpoint
The registry lists the primary outcome as Change in Weight, measured over 0 to 9 months.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | 95% Confidence Interval |
| Unit | kg |
| Endpoint classification | Continuous Endpoint |
The primary endpoint is change in weight, measured in kilograms, from baseline to 9 months. It is described as a mean, with a 95% confidence interval, and negative values are defined as weight loss. The registry further describes the outcome as broken out into 0-3months and 3-9months. The numerical mean changes and confidence intervals are not reported in the registry record, so the magnitude and precision of the observed changes cannot be assessed from that record.
Weight is a continuous measurement, so a mean change offers a concise description of the average direction and size of change in the analyzed group. It does not describe every participant’s trajectory: some individuals may have changes different from the mean. A confidence interval adds information about statistical precision. In general, it gives a range of values compatible with the data and the method used, while not guaranteeing that the true value lies within that interval.
The stated 0-to-9-month time frame defines the primary comparison. The two shorter intervals may help distinguish early from later change, but the registry does not report their estimates or explain whether they were planned as separate primary comparisons. Weight change is also only one part of the broader assessment. Changes in glucose and cardiac measures are listed as secondary outcomes, but their numerical findings are not reported in the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record identifies mean weight change from baseline to 9 months as the primary endpoint, but it does not report the estimate or its 95% confidence interval. Consequently, the direction, magnitude, and precision of the primary result cannot be described from the record. Although negative values are defined as weight loss, that definition alone does not establish what change was observed. The numerical results for the shorter weight-change intervals are also not reported in the registry record.
The design shapes what can be inferred. Participants were already undergoing bariatric procedures, and the registry does not describe random assignment or a control group. A change from baseline over follow-up can describe the experience of the observed cohort, but by itself it cannot separate the contribution of surgery from other changes occurring over time. Nor can it establish how outcomes would compare with an alternative treatment or with no surgery. The record also says that outcome analyses did not distinguish between the two procedure types, so it does not support a comparison between those procedures.
The follow-up account is more complete at the earlier visits than at the 2-year visit. The summary reports that all 43 participants completed the 3- and 9-month evaluations, while only 15 completed the 24-month evaluations because 28 were unwilling to return. In general, incomplete follow-up can affect interpretation if participants who return differ systematically from those who do not. The registry does not report an analysis of that possibility, so the direction or size of any resulting bias cannot be determined.
The record lists secondary changes in glucose, tissue Doppler diastolic velocity, and left ventricular mass, but their estimates are not reported in the registry record. It also does not report the statistical methods used for the outcome analysis beyond identifying the primary measure as a mean with a 95% confidence interval. No conclusion about the size or precision of the primary or secondary changes is warranted without their results. These limitations concern the information available in the registry record; they do not establish that analyses or results were absent from other sources.
9. Statistical Methods Explained
The primary outcome is a continuous measure: change in weight, in kilograms. For a continuous outcome, a mean summarizes the average observed change among the participants included in the analysis. It is a group-level description, not a claim that each participant changed by that amount. A mean can also be affected by unusually large or small individual values, so its interpretation is strongest when the distribution and analysis population are understood. The registry does not report those details.
The endpoint is accompanied by a 95% confidence interval. In general, a confidence interval describes statistical uncertainty around an estimate under the assumptions of the method used. A narrower interval indicates greater precision than a wider interval, but precision is not the same as freedom from bias. A confidence interval does not account automatically for missing follow-up, lack of a control group, or unmeasured differences. The numerical interval for weight change is not reported in the registry record, so its precision cannot be judged.
Change over time can be described using the difference between measurements at specified visits. Here, the primary time frame is 0 to 9 months, and the endpoint description also separates 0-3months and 3-9months. These intervals frame different portions of follow-up; they should not be treated as interchangeable estimates. The registry does not report the estimates for either interval or explain the calculation used to derive them. It also does not say whether each time interval was analyzed with a separate model or by another method.
Repeated measurements from the same participant are related: a person’s measurements over time are generally not independent observations. In general, a statistical method for repeated data should account for that dependence when it is relevant to the analysis. Treating correlated measurements as independent can misstate uncertainty. The registry does not identify a repeated-measures model or otherwise explain how within-participant dependence was handled, so no particular method should be assumed.
The record lists one analysis and four outcome measures, including weight change and secondary measures. It does not describe the statistical model, covariate adjustment, distributional assumptions, handling of outliers, or analysis population. Those details can affect both the estimate and its uncertainty. The record also does not report a p-value for the primary outcome. Without the result estimate and interval, neither statistical significance nor the compatibility of the result with different effect sizes can be assessed.
In general, over-dispersion means that observed variability is greater than a model’s assumptions anticipate. When present, it can make conventional uncertainty estimates too small unless the analysis accounts for it. Over-dispersion is most often a concern for certain count or event outcomes; the primary endpoint is continuous weight change. The registry does not report a diagnostic or analysis related to over-dispersion, and the record does not support a claim that it occurred.
The registry describes sample-size calculations as planning illustrations based on the observed effect, rather than as the trial’s own design justification. The stated assumptions are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the effect to detect expressed as a stated fraction of the observed effect. For non-time-to-event outcomes, such calculations are expressed as participants per arm. These are planning assumptions, not observed power, and the record does not report a trial-specific sample-size justification. Since no numerical observed effect or planning result is included in the record, a particular planning requirement cannot be stated.
A planning calculation asks how many participants might be needed under selected assumptions to detect a specified effect with a chosen statistical procedure. It does not show the probability that a completed study’s result is correct, nor does it establish that a study had a particular probability of detecting an effect after the fact. The stated illustrations also assume equal allocation between two arms, whereas the registry describes a cohort without a randomized control group. They should therefore be read as hypothetical planning scenarios, not as a description of the actual study design.
The registry does not report whether the analysis used unadjusted or adjusted estimates, how any uncertainty interval was constructed, or whether methods were changed from an original plan. The statistical plan, interim analyses, and sample-size justification are not reported in the registry record. Those omissions make it impossible to verify from the record whether the reported endpoint was analyzed according to a prespecified plan or to reproduce its analysis.
10. Multiplicity, Missing Data and Analysis Populations
The registry identifies a primary weight-change outcome and lists secondary changes in glucose, tissue Doppler diastolic velocity, and left ventricular mass. It also describes weight change across a primary 0-to-9-month time frame and shorter intervals. Considering several outcomes or time points raises a general multiplicity question: the more comparisons assessed, the more opportunities there may be for apparently notable findings by chance. Whether and how that concern was addressed is not reported in the registry record. No multiplicity adjustment or hierarchy among the secondary outcomes is described.
Missing follow-up is particularly relevant to the 2-year assessment. The summary reports that all 43 participants reportedly completed the 3- and 9-month evaluations, while only 15 completed 24-month evaluations because 28 were unwilling to return. In general, complete-case results can be biased if people with observed follow-up differ in outcome or other relevant characteristics from those without it. The reasons recorded for non-return do not establish whether missingness was related to outcomes.
The record does not report imputation, weighting, sensitivity analyses, or another method for handling missing measurements. It does not identify the analysis population or explain how participants with incomplete data were included. The adverse-event risk counts also differ from the cohort follow-up counts, and the criteria behind those denominators are not reported in the registry record. These details should not be inferred from the enrollment or follow-up summary.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Bariatric Surgery, Follow up at 9 Months | 0 | 37 | 0.0% |
| Bariatric Surgery, Follow up at 2 Years | 0 | 19 | 0.0% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Bariatric Surgery, Follow up at 9 Months | 0 of 37 |
| Bariatric Surgery, Follow up at 2 Years | 0 of 19 |
For the group labelled “Bariatric Surgery, Follow up at 9 Months,” the registry lists 0 serious adverse events among 37 participants at risk. It also lists 0 other adverse events among 37 participants at risk. For “Bariatric Surgery, Follow up at 2 Years,” it lists 0 serious adverse events among 19 participants at risk and 0 other adverse events among 19 participants at risk. No serious adverse-event terms are listed.
These entries describe reported counts in the specified groups; they do not establish that no adverse events occurred outside the recorded categories or observation periods. The deaths field is null for both groups, which means a death count is not reported in the registry record; it should not be read as zero. The basis for the risk denominators, the method of collecting events, and the handling of incomplete safety follow-up are not reported in the registry record.
Zero recorded events in a group is not proof that the underlying event risk is zero. In general, safety interpretation depends on how events were defined, actively collected, and followed, as well as how much information was available. The registry entries provide counts and denominators, but do not provide further detail about those procedures or the precision of an event-rate estimate.
12. What the Result Does, and Does Not, Mean
The registry record describes follow-up after bariatric surgery and names mean weight change from baseline to 9 months as the primary endpoint. It defines negative values as weight loss and mentions shorter intervals within the follow-up period. Because the numerical estimates and confidence intervals are not reported in the registry record, the amount and precision of weight change cannot be characterized. The listed metabolic and cardiac outcomes likewise have no numerical results in the record.
The design supports a description of measurements over time among the participants who were observed. It does not provide a randomized comparison with a control group, and the registry says participants were already undergoing surgery for clinical purposes. A before-and-after change in this cohort is not, by itself, a causal estimate of what surgery produced. Changes could also reflect other influences over time, and the record does not describe methods for separating those influences.
The record does not distinguish outcomes by the two procedure types participants received. It therefore does not establish whether those procedures had different outcomes. The incomplete 2-year follow-up also limits interpretation of the later observations: the summary reports that only 15 participants completed the 24-month evaluation because 28 were unwilling to return. The registry does not report how missing observations were handled or whether the returning participants were comparable to those who did not return.
These points do not imply that the study found no change or that no result exists outside the registry record. They define what can be concluded from the registered information: the study’s question, cohort follow-up, listed endpoints, and selected safety counts are described, but the principal outcome estimates and key analytic details are not. Any interpretation of the size, precision, or cause of outcome changes would require information not reported in the registry record.
13. Why This Trial Matters Statistically
This study illustrates a common statistical distinction between observing change and estimating a treatment effect. Measuring participants before and after an intervention can show how outcomes changed in the observed cohort. Without a randomized or otherwise suitable comparison, however, that pattern does not by itself isolate the intervention’s contribution from other influences over time. The registry describes follow-up after procedures that participants were already undergoing, not a randomized assignment.
It also highlights why endpoint definition and reporting matter. The primary outcome is clearly identified as mean weight change from baseline to 9 months, with a stated direction for negative values and a 95% confidence interval as the measure of dispersion. Yet the estimate and interval are not reported in the registry record. Without them, readers cannot judge the observed magnitude or statistical precision, even though the outcome and time frame are specified.
The follow-up description draws attention to missing data as a design and interpretation issue. The earlier visits are reported as completed by all 43 participants, while only 15 completed the 24-month assessment. The stated reason for non-return is unwillingness to return, but the record does not describe missing-data methods or evaluate whether those who returned differed from those who did not. This is important because later follow-up can describe a selected subset if retention is related to outcomes.
Finally, the record lists several outcomes and more than one follow-up interval, making clear why analysis plans should specify which comparisons are primary and how additional analyses are interpreted. The registry does not report a multiplicity strategy or detailed statistical plan. Together, these features make the record useful for understanding the study’s structure while limiting the strength and detail of statistical conclusions that can be drawn from the registered information.
14. 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 primary endpoint is that its numerical mean change and confidence interval are not reported in the registry record. The definition and time frame are stated, but neither the size nor precision of the observed change can be assessed. Numerical results for the listed secondary outcomes are also not reported in the registry record.
The study description does not include a randomized control group. Participants were already undergoing surgery, and the procedures were not assigned as part of the research. This limits causal interpretation of changes over time. The registry also says that outcome analyses did not distinguish between the two procedure types, preventing a procedure-specific comparison from the recorded analysis.
Follow-up completeness differs by time point. The summary reports complete 3- and 9-month evaluations for all 43 participants, but only 15 completed 24-month evaluations, with 28 unwilling to return. The record does not report how missing observations were handled, whether the later analysis accounted for non-return, or whether participants who returned differed from those who did not. The analysis population is not reported.
Statistical details are limited: the model, covariate adjustment, confidence-interval construction, multiplicity approach, and original sample-size justification are not reported in the registry record. The safety denominators are also not explained, and death counts are null rather than reported as zero. These gaps limit independent assessment and reproduction of the analyses.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Metabolic Parameters 3 Months, 9 Months, and 2 Years After Bariatric Surgery — NCT00178633.
- Registry record last updated 2020-11-23; status last verified 2020-11.
- Results first posted 2014-09-11.
- 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.
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18. Record Summary
The registry describes a completed cohort study of bariatric surgery follow-up, with enrollment of 43 participants and weight change from baseline to 9 months as the primary outcome. Participants were already undergoing clinical procedures; the research involved assessment and follow-up. The record says outcomes were not separated by the two procedure types.
Assessments are described at baseline, 3 months, and 9 months, with 2-year follow-up also reported. The summary states that all 43 participants reportedly completed 3- and 9-month evaluations, while only 15 completed the 24-month evaluation because 28 were unwilling to return. Listed secondary outcomes include changes in glucose, tissue Doppler diastolic velocity, and left ventricular mass.
The numerical primary and secondary outcome results, detailed statistical methods, missing-data methods, and multiplicity approach are not reported in the registry record. Safety entries list zero serious and zero other adverse events in the specified groups; death counts are not reported.