Study of Stapled Transanal Rectal Resection (STARR) Surgery in Refractory Constipation Associated With Obstructive Defecation Syndrome (ODS): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Study of Stapled Transanal Rectal Resection (STARR) Surgery in Refractory Constipation Associated With Obstructive Defecation Syndrome (ODS) (NCT00256984), a non-randomized phase 4 study. The primary outcome is Percentage of Change (Reduction) in Total ODS Symptom Composite Score From Baseline to One Year Post Procedure.

2. Clinical Question

3. Trial Design

The registry describes a completed, Phase 4, multicenter study with non-randomized allocation, no masking, and a single-group model. The registered enrollment was 75. The intervention was STARR surgery using the Transtar (PROXIMATE®) 33 mm Circular Stapler. Ethicon Endo-Surgery is listed as the sponsor.

The study focused on obstructive defecation syndrome and associated refractory constipation. The primary endpoint was assessed in a per-protocol population. The registry record does not report the criteria for inclusion in that population, how many participants contributed to the primary endpoint, or whether every enrolled participant completed follow-up. Those details matter because an analysis limited to participants meeting protocol criteria can differ from an analysis of everyone who entered a study.

The absence of randomization and a separate comparator has important consequences for interpretation. A change between baseline and follow-up can be described, but the design alone cannot establish that the change was caused by the procedure. Other explanations, including the natural course of symptoms, concurrent care, expectations, and changes in how symptoms are reported, cannot be separated from the procedure’s association with the outcome using a single-group comparison.

The registry lists secondary symptom and quality-of-life outcomes at several follow-up points, including 1 Month, 6 Months, and 12 Months. Their listing indicates the scope of outcomes registered, not that results for each are available. The registry record does not report results for those outcomes in the registry record for this analysis.

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

Analysis population for the primary outcome, as defined in the registry: Per protocol

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 Change (Reduction) in Total ODS Symptom Composite Score From Baseline to One Year Post Procedure, measured over one year from Baseline.

The primary endpoint was the percentage of change in total ODS symptom composite score from baseline to one year after completion of the procedure. The registry describes the score as 0 for worst and 24 for best. It identifies the endpoint as a mean of a continuous measure, with standard deviation as the dispersion measure, and specifies a per-protocol population.

A symptom composite can bring several aspects of a condition together in one measure. Repeated assessment allows investigators to describe how the score at follow-up compares with baseline. Percentage change is intended to express change relative to the baseline score, rather than only reporting an absolute score difference. The precise formula used to calculate the percentage change, including how direction and baseline values were handled, is not reported in the registry record.

The endpoint was selected to assess symptom change over the stated follow-up period, consistent with the study’s stated interest in symptom relief and durability. A mean summarizes the average result across the analyzed population, while the standard deviation describes variation among individual results. Neither statistic alone shows the uncertainty around the estimated mean. The observed mean, standard deviation, and a confidence interval for the primary endpoint are not reported in the registry record. Therefore, the endpoint’s intended meaning can be described, but its observed magnitude and precision cannot be assessed from the posted primary result.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does the mean describe?

For a continuous outcome, the mean is the arithmetic average of the observed measurements in the analyzed population. In this study, the registered primary measure is the mean percentage of change in the ODS symptom composite score from baseline to one year after the procedure. A mean is a compact description of the group’s average result; it does not imply that every participant had a result close to that average. Individual responses can vary, and the mean can be affected by particularly high or low observations.

The registry identifies the standard deviation as the measure of dispersion. In general, a standard deviation describes how spread out individual measurements are around the mean. It is not the same as a confidence interval: the standard deviation concerns variation among observations, whereas a confidence interval expresses uncertainty about an estimated quantity. The primary mean and standard deviation are not reported in the registry record, so neither the average change nor the spread of participant results can be discussed numerically.

What does percentage change add?

In general, a percentage-change measure expresses change in relation to a baseline value. That can make a change easier to relate to the starting measurement, but it also makes the calculation depend on the baseline and on the exact formula. The registry describes the outcome as a percentage of change or reduction, but the formula is not reported in the registry record. The score is described as 0 for worst and 24 for best. Because the formula and observed estimate are unavailable, the direction and magnitude of a percentage result should not be reconstructed or assumed.

What can a confidence interval tell a reader?

In general, a confidence interval gives a range of values compatible with the data and the statistical procedure used to calculate it. A narrower interval indicates greater precision under that procedure, while a wider interval indicates greater uncertainty. An interval’s interpretation depends on the design, assumptions, and analysis population. No confidence interval for the primary endpoint is reported in the registry record. Its limits therefore cannot be described, and the estimate’s precision cannot be assessed from the posted primary result.

What does the single-group design permit?

A single-group before-and-after design can describe how measured outcomes differ between baseline and follow-up among participants with observations at both times. It does not directly estimate the contrast between receiving the procedure and receiving a comparator under otherwise comparable conditions. Without random allocation and a concurrent control group, changes can reflect factors other than the intervention, such as the course of symptoms, other care, expectations, or differences in measurement and reporting. These are general design considerations, not findings about what occurred in this study.

No masking was registered. In general, knowledge of treatment or study participation can affect self-reported outcomes, assessment, or other behavior. The registry entries do not establish whether or how any such influence affected these results. Since the main outcome is a symptom composite, the absence of masking is relevant to interpretation, but it does not by itself establish the direction or size of bias.

What do the planning assumptions mean?

In general, sample-size calculations estimate how many observations a hypothetical study might require under chosen assumptions about the effect to detect, statistical significance, allocation, and outcome variability. They are planning illustrations, not observed power and not results from the trial. The registered planning description refers to a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the effect defined as a stated fraction of the observed effect. It also distinguishes total events for time-to-event calculations from participants per arm for other calculations.

Those assumptions describe a hypothetical two-arm planning exercise and should not be mistaken for this trial’s design, which was single-group and non-randomized. No calculated sample-size values or observed primary effect are included in the registry entries. The trial’s own sample-size justification and statistical plan are not reported in the registry record. The planning assumptions cannot fill those gaps or establish what design choices were made for the study.

What can be concluded from the available analysis information?

The registry identifies the endpoint type, summary statistic, dispersion measure, timeframe, and per-protocol population, but reports no analyses in the registry record. It does not describe model specifications, covariate adjustment, assumptions checks, or sensitivity analyses. General statistical methods can explain what such choices are intended to address, but no particular method should be attributed to this study unless the registry record reports it.

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("Stapled Trans-Anal Rectal Resection (STARR)")
n   <- c(59)
m   <- c(60.8)
sp  <- c(35.46)
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  Stapled Trans-Anal Rectal Resection (STARR)  59  60.800  35.460  51.559  70.041

11. Multiplicity, Missing Data and Analysis Populations

The registry lists a primary endpoint and several secondary outcomes involving ODS symptoms, PAC SYM symptom severity and frequency, PAC QOL, and SF-12 physical and mental quality-of-life components. Considering multiple outcomes can raise a multiplicity issue: in general, the more statistical tests performed, the greater the chance that at least one result may appear unusual by chance. Researchers may address this through a prespecified hierarchy, adjustment, or other strategy. The registry record does not report a multiplicity strategy or the results of analyses for these outcomes.

The number of outcome measures is listed as 7, while the number of analyses is listed as 0. These registry fields do not provide the statistical analysis plan or establish which analyses were conducted outside the registry record. The trial’s prespecified testing sequence, any adjustment for multiple comparisons, and any interim analyses are not reported in the registry record. No inferential claim about a secondary outcome should be inferred from its inclusion in the outcome list.

The primary endpoint population is per protocol, but the registry record does not state the protocol criteria, the number analyzed, or how missing measurements were handled. In general, missing outcome data can reduce precision and can bias an estimate if availability is related to the outcome. Complete-case analysis, imputation, and sensitivity analysis each rely on assumptions; the choice and assumptions cannot be determined from the available description.

It is also not reported in the registry record whether the primary analysis included all enrolled participants, whether deviations from the protocol led to exclusions, or whether reasons for missing data were summarized. These gaps prevent assessment of how representative the analyzed population was and how robust the result might be to missing observations. They do not establish that missingness or multiplicity affected the study’s findings; they identify information needed to evaluate that possibility.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: postprocedural haemorrhage (2.7%), urinary retention (2.7%), blood count abnormal (1.3%), breast cancer (1.3%), colostomy (1.3%).

The safety record lists 75 participants at risk for serious adverse events and 14 affected. It also lists 75 at risk for other adverse events and 33 affected. These are the registry’s reported counts; they should not be converted into rates by inference. The death count is not reported in the registry record.

The most frequent serious adverse event terms listed are postprocedural haemorrhage and urinary retention, each at 2.7%. Blood count abnormal, breast cancer, colostomy, and diabetic ketoacidosis are each listed at 1.3%. These percentages describe the entries as recorded; the available information does not explain event attribution, timing, severity grading beyond the serious category, or whether one participant could contribute more than one event term.

Safety counts in a single-group study describe events recorded among participants at risk, but do not by themselves show that the procedure caused an event. There is no concurrent control group in this design for comparison of event frequency. The registry record does not report further details needed to assess the events’ course or relationship to the procedure. The listed figures should therefore be read as descriptive safety information, not as a comparative estimate of risk.

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

The registry record establishes that a Phase 4, non-randomized, single-group study assessed STARR surgery for obstructive defecation syndrome. It defines a primary symptom endpoint based on percentage change in the ODS symptom composite score from baseline to one year after the procedure. It also lists secondary symptom and quality-of-life outcomes and reports adverse-event counts and selected serious event terms.

What the posted information does not establish is the observed primary endpoint result. The primary mean and standard deviation are not reported in the registry record, and no confidence interval or p-value is included in the registry record considered for this analysis. Therefore, the amount of symptom change, its variability, and the precision of any average estimate cannot be stated. The study’s stated interest in effectiveness and durability is a research question, not itself evidence of a particular outcome.

Even if a before-and-after estimate were available, the single-group, non-randomized design would not isolate the effect of the procedure from other changes over time. There is no like-for-like randomized control comparison in the registered design. A measured change would describe the analyzed participants’ outcomes, but would not alone determine what caused that change.

The safety entries provide descriptive counts and percentages, not a comparison with another treatment or with no procedure. They do not establish causation. The per-protocol label also leaves questions about who was analyzed and how missing measurements were handled; those details are not reported in the registry record.

Thus, the record is informative about the study’s purpose, design, endpoint definition, and selected safety reporting, but it is insufficient for a quantitative judgment about the primary symptom result, its precision, or a causal treatment effect. That distinction separates what was planned and measured from what the available outcome data can substantiate.

14. Why This Trial Matters Statistically

This study is statistically instructive because its clinical question is framed around change in symptoms over time, while its design is a single-group assessment. Such studies can describe outcomes after an intervention and can be useful for documenting symptom measures and safety events. Their interpretation nevertheless differs from a randomized comparison: without a concurrent comparator, a change from baseline cannot separate the intervention’s contribution from other influences.

The endpoint also illustrates the importance of defining a measure precisely. The ODS symptom composite has a stated direction, from 0 as worst to 24 as best, and the primary endpoint is described as percentage change or reduction. The exact calculation is not reported in the registry record. Readers need the formula and observed estimate to understand how to interpret direction and magnitude, rather than relying on an endpoint label alone.

Precision is another central issue. A mean and standard deviation were specified as the summary approach, but their primary endpoint values are not reported in the registry record. Without the estimate and a measure of its uncertainty, it is not possible to judge how stable or precise the result is. The per-protocol population designation further makes the analysis population important: eligibility rules, participant flow, and missing-data handling affect how broadly an estimate can be interpreted.

Finally, the registry contains safety counts but no comparator. This supports a descriptive reading, not a comparative safety conclusion. Taken together, the study highlights why design, endpoint definitions, analysis populations, uncertainty, and complete result reporting must be considered together when reading clinical trial evidence.

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.

Several trial-specific details needed to interpret the primary outcome are not reported in the registry record: the observed mean percentage change, its standard deviation, a confidence interval, and a p-value. The precise percentage-change formula is also not stated. Consequently, the primary estimate’s direction, magnitude, variability, and precision cannot be assessed from the available results.

The study is non-randomized and single-group, with no masking. It has no concurrent control group to help distinguish a change associated with the procedure from other changes over time. This limits causal interpretation irrespective of whether an observed before-and-after difference is large or small. The registry entries do not identify which alternative influences, if any, affected participants’ outcomes.

The per-protocol population is named, but its criteria and analyzed participant count are not reported in the registry record. Follow-up completeness, reasons for missing outcome data, exclusions, and the approach to missing measurements are also not reported. These omissions limit assessment of selection and potential bias in the analyzed population.

The registry lists multiple secondary outcomes, but their observed results and any strategy for handling multiple testing are not reported in the registry record. The statistical analysis plan, sample-size justification for the actual study, and interim analysis details are not reported either. The planning assumptions describe a hypothetical two-arm calculation and should not be treated as the study’s own design rationale.

For safety, the record gives counts and selected serious-event terms, but does not report a control comparison or further event-level details such as timing and attribution. These limitations constrain interpretation of both benefits and harms; they do not establish that a bias or safety problem occurred.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Study of Stapled Transanal Rectal Resection (STARR) Surgery in Refractory Constipation Associated With Obstructive Defecation Syndrome (ODS) — NCT00256984.
• Registry record last updated 2018-07-16; status last verified 2017-10.
• Results first posted 2011-04-07.
• 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, Phase 4, multicenter, non-randomized, unmasked, single-group study of STARR surgery for obstructive defecation syndrome. Registered enrollment was 75. The primary endpoint was percentage change in total ODS symptom composite score from baseline to one year after the procedure, in a per-protocol population. The score is described as 0 for worst and 24 for best.

The primary endpoint’s observed mean and standard deviation are not reported in the registry record. Secondary outcomes include symptom and quality-of-life measures. Safety reporting lists 14 affected among 75 at risk for serious adverse events and 33 affected among 75 at risk for other adverse events; the death count is not reported in the registry record. The single-group design does not provide a randomized, concurrent comparison for causal interpretation.