Comparison of Bowel Cleansing Efficacy Between Same-day Dose Versus Split Dose: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Comparison of Bowel Cleansing Efficacy Between Same-day Dose Versus Split Dose (NCT03315949), a randomized phase 3 study. The primary outcome is Boston Bowel Preparation Scale.

2. Clinical Question

3. Trial Design

This was a prospective randomized controlled trial conducted at a single center, according to the official title. The registry identifies it as phase 3, randomized, double-masked, and parallel-group. The official title also describes the trial as operator blinded. The registry does not explain who was masked or how masking was maintained, so the masking details cannot be assessed from the record.

The recorded enrollment was 352. Participants were randomly assigned to same-day dose or split-dose PEG. The study involved people having colonoscopy for various reasons, and procedures took place between 10 AM to 6 PM. The registry describes PEG ingestion instructions for each schedule, including the timing of the previous-evening dose in the split-dose group and the day-of-procedure dosing in the same-day group. It also states that participants were instructed to ingest 500ml PEG every 15 minutes.

The registry lists the study as completed. Its recorded start date is 2017-05-01 and its primary completion date is 2018-02-28. The sponsor is Incheon St.Mary's Hospital. These registry entries describe the trial’s organization and timing, but they do not provide information about allocation concealment, protocol deviations, adherence to the assigned cleansing schedule, or the way randomization was generated. Those details are not reported in the registry record.

The posted primary outcome is a count of successful bowel cleansing, rather than a posted arm-level average BBPS score. The outcome counts are 169 in the same-day dose group and 163 in the split-dose group, with arm counts listed as 171 and 166 respectively. The record does not explain the difference between these outcome counts and the group counts listed for adverse events. It also does not post an inferential analysis comparing the randomized groups.

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

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: Participants who ingested bowel cleansing agent according to protocol

6. Primary Endpoint

The registry lists the primary outcome as Boston Bowel Preparation Scale, measured over Bowel cleansing efficacy using Boston bowel preparation scale will be assessed during colonoscopy withdrawal.

The primary endpoint concerns successful bowel cleansing assessed during colonoscopy withdrawal with the Boston Bowel Preparation Scale (BBPS). The registry defines success as a score of 2 or above in all segments. It describes the BBPS as the sum of scores for 3 bowel segments, with a total scale from 0-9; the listed category descriptions are 0=inadequate, 1=poor, 2=good, and 3=excellent.

This endpoint turns the cleansing assessment into a count of participants meeting a stated criterion. That can be easier to interpret as a practical outcome than a score alone: success requires each segment to reach the specified threshold, rather than allowing a higher score in one segment to compensate for a lower score elsewhere. The score is assessed during the procedure, linking the measure to the colonoscopy examination.

As a general statistical point, a clear endpoint definition helps readers understand what an outcome count represents and how it might differ from a continuous scale score. The posted endpoint is the number of successful cleansings, not the distribution of total BBPS scores or the average score in each arm. The registry does not post segment-level scores, a participant-level score distribution, or further details about how the assessment was conducted. It also does not post the results of a statistical comparison of the success counts.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies a randomized, parallel-group trial. In a randomized study, assignment to groups is based on a chance process rather than solely on participant or clinician choice. As a general statistical principle, randomization is intended to make the groups comparable, on average, with respect to factors measured and unmeasured at baseline. It does not guarantee identical groups in a particular trial. The registry record does not describe the random sequence method, allocation concealment, or any balance assessment.

What does a parallel-group design mean?

In a parallel-group design, participants are assigned to one of the study schedules and outcomes are compared between groups. Here, the schedules were same-day PEG and split-dose PEG. The registry does not indicate that participants crossed over between schedules. The parallel design means the result depends on comparing different participants assigned to each schedule, rather than comparing each participant’s outcome under both schedules.

What does masking tell us?

The registry records double masking, while the official title calls the study operator blinded. Masking is a design feature intended to limit how knowledge of assigned treatment may influence conduct or assessment. However, the record does not identify which parties were masked, explain the procedures used to preserve masking, or state whether masking was successful. It is therefore possible to report the registry’s labels, but not to infer the practical extent of masking.

How should the endpoint be analyzed?

The primary measure is a count of participants whose BBPS score was 2 or above in every segment. For a binary endpoint such as meeting or not meeting a success criterion, a statistical comparison can estimate the difference or ratio between groups and quantify uncertainty. This is general statistical context, not a description of an analysis reported for this trial. The registry posts the arm counts but no effect estimate, confidence interval, or hypothesis-test result. It lists zero analyses and notes that a two-arm comparison was not estimable for this count outcome.

The distinction between an endpoint count and an analysis is important. Counts describe the observed data in each group. An analysis applies a statistical method to estimate a contrast and its uncertainty, according to a specified approach. Without the method and its result, readers cannot evaluate the evidence for a difference using a prespecified inferential framework. No adjusted analysis, covariate set, or model specification is reported in the registry record.

Why does uncertainty matter?

As a general explanation, an estimate based on trial participants is subject to sampling variability: a different set of participants could yield different observed results. A confidence interval is one way to communicate the uncertainty around an estimated contrast. Its width reflects both the information in the data and the statistical method used. Since no contrast or interval is posted, the precision of the comparison cannot be evaluated from the registry outcome information. The counts should not be converted into an unreported inferential conclusion.

General statistical methods also depend on assumptions. For example, comparisons of binary outcomes require a defined estimand, an analysis population, and an approach to participants with missing outcome information. The registry does not report these choices. The outcome counts and group sizes differ from the adverse-event risk sets, but the record does not say why. That alone does not identify how missing outcomes were handled or whether any participant was excluded from a particular analysis.

What can be said about planning?

A trial’s sample-size justification describes the assumptions and target precision or power used when planning enrollment. The registry does not report a trial-specific sample-size justification, target effect, or interim-analysis plan. As a general principle, a planning illustration based on an observed effect is not a measure of the trial’s observed power. Such an illustration depends on its assumptions and should not be treated as evidence that an effect has been established. No numeric planning estimates are reported in the registry record.

The analysis plan is also not described in enough detail to determine whether any analyses were intended to be adjusted, whether outcomes were to be analyzed by randomized assignment, or how deviations from assigned preparation would be treated. Those details are not reported in the registry record. The appropriate interpretation is consequently descriptive: the posted primary outcome gives group counts under the stated endpoint definition, without a posted statistical estimate of the difference between schedules.

10. Multiplicity, Missing Data and Analysis Populations

The registry’s brief description says that the study aimed to compare bowel-cleansing efficacy, adverse events, and patient tolerability. It posts one outcome measure, the successful-cleansing count, and no secondary posted outcomes. The registry does not report a multiplicity strategy, such as a hierarchy of outcomes or an adjustment for testing several hypotheses. Since no analysis results are posted, the impact of any multiplicity decisions cannot be assessed.

Missing-data handling is not described. The primary outcome lists group counts of 171 for same-day dose and 166 for split-dose, while the adverse-event figures list 172 and 167 at risk. The registry does not explain these differences or state whether they reflect missing outcome assessments, different analysis populations, or another accounting convention. No imputation method or sensitivity analysis is reported. These counts should not be treated as evidence of a particular missing-data mechanism.

The record also does not define the analysis population used for the primary outcome. It does not say whether the primary analysis followed randomized assignment, included only participants who completed colonoscopy, or used another population. No protocol deviations, withdrawals, or exclusions are described in the posted outcome information. These omissions limit assessment of whether the analyzed groups retain the benefits of randomization.

As a general statistical principle, readers need to know which outcomes and analyses were prespecified, how missing observations were handled, and which participants entered each analysis to assess risk of selective reporting and bias. Those details are not reported in the registry record. The available information supports describing the registered counts, but not reconstructing the intended analysis plan.

11. 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 5% reporting threshold.

Most frequent non-serious adverse event terms

The registry reports zero serious adverse events among 172 participants at risk in the same-day dose group and zero among 167 participants at risk in the split-dose group. Deaths are reported as zero in both groups. These are the serious-event figures recorded for the listed risk sets; they do not provide details about the definition of a serious event, the observation period, or event ascertainment. Those details are not reported in the registry record.

The aggregate count for other adverse events is 73 in the same-day dose group and 67 in the split-dose group. These figures are counts of participants affected as recorded, not a comparison adjusted for follow-up or other factors. Specific types of these other adverse events are not reported in the registry record. No serious adverse-event terms are listed.

As a general statistical point, zero observed serious events does not demonstrate that the underlying risk is zero. The observed count and the number at risk describe what was recorded in this study; they do not establish how frequently serious events might occur in other settings. No comparative safety estimate, confidence interval, or test result is posted. The registry’s adverse-event figures should therefore be read as descriptive counts rather than evidence that one preparation schedule has a different safety profile.

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

The registry record documents a randomized comparison of two PEG preparation schedules and posts successful-cleansing counts for the primary endpoint. It also records aggregate adverse-event counts. These results describe what was posted for the enrolled trial groups; they do not, on their own, quantify the uncertainty in a between-group difference. No inferential comparison is reported.

The primary endpoint has a specific all-segment threshold, so its counts concern participants who met that definition, not every aspect of bowel preparation quality. A count does not show the distribution of BBPS scores, the score in each segment, or how close participants who did not meet the endpoint were to the threshold. Those details are not reported in the registry record.

The result does not establish that the two schedules are equivalent, nor does it establish a statistically supported difference. Equivalence requires a defined margin and a suitable analysis; neither is reported. The absence of a posted p-value or confidence interval is not evidence that the groups are the same. It means the registry does not provide the statistical estimate needed to assess the contrast’s magnitude and precision.

Nor do the posted outcomes establish the experience of participants in terms of tolerability. Although tolerability was part of the stated study aim, no secondary outcome is posted for it. Similarly, aggregate adverse-event figures do not give details of event types or a formal comparison. The registry record does not report adherence, protocol deviations, or the results of subgroup analyses.

As a general interpretation principle, trial findings are most informative when the outcome definition, analysis population, effect estimate, uncertainty, and analysis methods can all be examined together. In this record, the endpoint definition and group counts are available, but key analysis details and comparative estimates are not. The appropriate conclusion is therefore limited to describing the posted counts and recognizing that the comparative statistical evidence is not reported.

13. Why This Trial Matters Statistically

This trial is statistically interesting because the schedules differ mainly in the timing of PEG ingestion, while the primary outcome is defined by a specific all-segment cleansing threshold. That combination raises a clear comparison question: whether the two timing approaches differ in the number of participants who reach the stated cleansing criterion. Random assignment is an appropriate design feature for studying such a comparison, because it is intended to reduce systematic differences between groups.

For readers, however, a randomized design is only part of the evidence. The registry posts the primary outcome counts but no comparative estimate or measure of precision. Without those, the observed results cannot show how large or uncertain a group difference may be. The record also does not explain the participant counts used for the primary outcome versus those at risk for adverse events. Clear reporting of analysis populations and missing-data handling would help readers interpret the outcome counts alongside the randomized design.

The endpoint itself illustrates why operational definitions matter. Defining success as a score of 2 or above in every segment makes the outcome interpretable, but reduces a multi-segment score to whether a threshold is met. That approach can answer a focused question while leaving other aspects of score variation unreported. The registry does not provide segment-level results or the full score distribution.

Finally, the study’s stated interest in adverse events and tolerability extends beyond its posted primary outcome. Only aggregate adverse-event figures are available, and no tolerability results are posted. This highlights a general reporting principle: aims, outcome definitions, analysis plans, and complete results all contribute to a statistical interpretation. The registry record offers useful design and descriptive information, but not the full set of details needed to evaluate comparative efficacy, precision, or tolerability.

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 primary limitation for interpreting the comparative result is that the registry posts no statistical analysis of the successful-cleansing counts. There is no reported effect estimate, confidence interval, or hypothesis-test result. The raw counts cannot establish the magnitude or precision of the difference between schedules. No equivalence or non-inferiority margin is reported, so the results cannot be read as establishing equivalence.

The registry identifies the study as single center, which limits the settings directly represented by the trial. It describes participants undergoing colonoscopy for various reasons but does not report participant characteristics in the outcome information. The extent to which the enrolled groups represent other populations cannot be determined from the record.

The group counts used for the primary outcome differ from the adverse-event risk sets. The registry does not explain the difference, report the primary analysis population, or describe how missing data and exclusions were handled. It also does not report adherence to the assigned schedules or protocol deviations. These omissions make it difficult to assess the relationship between random assignment and the posted outcome counts.

Masking is described as double in the registry and operator blinded in the official title, but the people masked and the masking procedures are not specified. The randomization method and allocation concealment are also not reported. These are relevant details for judging how assignment and outcome assessment were conducted.

Finally, no secondary outcomes are posted despite the stated aim to assess adverse events and tolerability. Serious-event counts are available, but the registry does not provide event definitions or specific other-event terms. The limits of the record concern what can be evaluated from its posted information; they do not establish that unreported procedures or analyses did not occur.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Comparison of Bowel Cleansing Efficacy Between Same-day Dose Versus Split Dose — NCT03315949.
• Registry record last updated 2020-08-13; status last verified 2020-08.
• Results first posted 2020-08-13.
• 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.

18. Record Summary

The registry record describes a completed, phase 3, prospective randomized controlled trial at a single center, comparing same-day with split-dose PEG before colonoscopy. It lists double masking and a parallel-group design; the official title describes operator blinding. The recorded enrollment is 352, and colonoscopies took place between 10 AM to 6 PM.

The primary endpoint was successful cleansing, defined as a BBPS score of 2 or above in every segment. Posted counts are 169 in the same-day dose group and 163 in the split-dose group. The record also reports zero serious adverse events and zero deaths in each group, alongside aggregate counts for other adverse events. It posts no secondary outcomes or statistical analyses, and no comparative estimate or confidence interval is reported. The analysis populations, missing-data handling, masking procedures, and trial-specific sample-size justification are not reported in the registry record.