Cap-assisted Water Immersion Versus Water Immersion Colonoscopy: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Cap-assisted Water Immersion Versus Water Immersion Colonoscopy (NCT01547247), a randomized na study. The primary outcome is Cecal Intubation Time.

2. Clinical Question

3. Trial Design

This was a prospective, randomized, single-center trial with a parallel-group design. The registry describes masking as single, but does not report which people involved in the trial were masked or how masking was implemented. The sponsor was Vitkovice Hospital. The study status is completed, with a registry enrollment of 208. The record lists a start in 2012-01 and primary completion in 2012-05.

Participants were assigned to cap-assisted water immersion colonoscopy or water immersion colonoscopy without an attached cap. Both groups had water immersion during insertion and room air insufflation during withdrawal. This shared procedure is important to interpreting the comparison: the randomized contrast is the use of a cap within a water-immersion approach, not a comparison of water immersion against a different insertion technique.

The posted primary outcome summaries list 98 participants in each arm. The relationship between those arm counts and the registry enrollment is not explained in the registry record. The number randomized, the number included in each outcome analysis, and any exclusions or losses after randomization are not described separately. Further details about random sequence generation, concealment of allocation, recruitment, eligibility criteria, and the identity of the masked party are not reported in the registry record.

The trial’s stated sample-size planning used a clinically relevant difference of 20 % in intubation times and specified 93 subjects per arm. The stated assumptions included a two-tailed alfa 0.05 and beta 0.2. No further details of the calculation, such as the assumed variability, are reported in the registry record. The trial record lists two secondary outcomes: patient comfort during insertion and success rate of minimal-sedation colonoscopy. Results for these outcomes are 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.

Before assignment: * a total of 275 subjects assessed for eligibility * a total of 208 patients eandomized after exclusion of 67 due to not fulfilled inclusion criteria * a total of 196 subjects analyzed after exclusion of 12 patients (poor bowel preparation, IBD, malignant obstruction, protocol deviation, ischemic colitis)

Overall Study

Analysis population for the primary outcome, as defined in the registry: Statistical power was calculated for the primary endpoint. A sample size of 93 subjects per arm was calculated using two-tailed alfa 0.05, beta 0.2, assuming that difference 20 % in intubation times would have been clinically relevant.

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 Cecal Intubation Time, measured over 3 months.

Cecal intubation time is the trial’s primary endpoint. The registry defines it as the time between introducing the colonoscope into the anus and reaching the cecum. It is recorded in minutes, and the registry lists a timeframe of 3 months. The endpoint therefore captures the duration of the insertion phase up to the specified anatomical destination, rather than the duration of the entire colonoscopy.

This measure was selected to address the investigators’ stated expectation that the cap might shorten insertion time. In a randomized comparison, an outcome measured consistently in both groups can describe whether the groups’ recorded insertion times differ. It does not by itself describe patient comfort, successful completion under minimal sedation, or other aspects of the procedure. Those are separate outcomes; the registry names comfort during insertion and success rate of minimal-sedation colonoscopy as secondary outcomes.

The posted values are 6.9 minutes for cap-assisted water immersion colonoscopy, with a 95% confidence interval of 4.0 to 9.8, and 7.4 minutes for water immersion colonoscopy without a cap, with a 95% confidence interval of 3.2 to 11.6. The registry does not specify in the endpoint description whether these arm-level values are means or another summary, nor does it post a comparative estimate or test. The values should therefore be read as the recorded arm summaries and their stated intervals, not as a complete estimate of the between-group effect.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does randomization contribute?

Randomization assigns participants to study groups through a chance-based process. When implemented appropriately, it is intended to make the groups comparable, on average, with respect to factors that might influence an outcome. It supports interpreting a group contrast as an effect of the assigned intervention, subject to trial conduct, outcome measurement, and analysis. Randomization does not guarantee identical groups, especially in a study of limited size, and it does not remove uncertainty in an estimate.

The registry identifies this study as randomized and parallel, with cap-assisted water immersion colonoscopy compared with water immersion colonoscopy without a cap. Details of sequence generation and allocation concealment are not reported in the registry record. The masking designation is single, but the party masked and the procedures used to maintain masking are not reported. These omissions limit the reader’s ability to assess how allocation and awareness of treatment assignment might have affected conduct or measurement.

How should the confidence intervals be read?

A confidence interval gives an interval estimate together with a stated confidence level. In general, it communicates the uncertainty associated with an estimate under the method used to calculate it. A narrower interval indicates greater precision under that method; a wider interval indicates less precision. A confidence interval does not mean that individual observations fall within its endpoints, and it is not a guarantee that the true value lies in that particular interval.

The registry reports arm-level cecal intubation time values with 95% confidence intervals: 6.9 minutes (4.0 to 9.8) for the cap-assisted arm and 7.4 minutes (3.2 to 11.6) for the arm without a cap. It does not report the calculation method or an interval for the between-group contrast. As a result, readers cannot use these arm intervals alone as a direct estimate of the precision of the treatment comparison. A comparative interval would express uncertainty about the contrast itself.

What is the role of the planned sample size?

The registry states that the planned sample size was 93 subjects per arm, based on a difference of 20 % in intubation times considered clinically relevant, two-tailed alfa 0.05, and beta 0.2. In general, a sample-size calculation uses assumptions about the effect to detect, outcome variability, significance level, and desired probability of detecting that effect under the planning model. The registry does not report all of those details, including the variability assumption or the full calculation.

These planning figures do not establish what the trial observed, and they do not show the probability that the trial detected an effect after the results were known. A planned target is distinct from the number contributing data to an outcome. Although the registry reports 98 participants in each primary-outcome arm summary, the analysis population and handling of missing outcome measurements are not reported. The planning description should therefore be understood as the stated design rationale, not as evidence of a particular degree of statistical certainty in the final comparison.

Why does the comparative analysis matter?

A treatment comparison generally needs an effect estimate that directly contrasts groups, with an accompanying measure of uncertainty and, where appropriate, a test against a stated null hypothesis. The arm-level values describe each group separately. A direct contrast would indicate the estimated difference in cecal intubation time between the randomized strategies, while its confidence interval would show the uncertainty around that difference. A p-value, if reported, would address compatibility of the data with a specified null model; it would not measure the size or clinical importance of an effect.

No primary-outcome comparative estimate, p-value, or analysis method is reported in the registry record. The record lists zero analyses. Thus, there is no posted basis for describing the primary outcome as statistically significant or not statistically significant. Nor can the reader determine whether the analysis adjusted for any factors, used a particular distributional assumption, or followed an intention-to-treat approach. Those details are not reported in the registry record.

What do the endpoint and its scale represent?

Cecal intubation time is a continuous time measure, recorded in minutes. The registry’s definition starts the clock when the colonoscope is introduced into the anus and ends it when the cecum is reached. This operational definition provides a specific target for outcome measurement. However, the registry does not report details such as timing equipment, rules for failed or repeated insertion, or how values were handled if the cecum was not reached. The secondary outcomes concern comfort during insertion and success of minimal-sedation colonoscopy; their posted results and measurement details are not reported in the registry record.

In general, analysis of a continuous outcome depends on the distribution of observed values and the method used to estimate group summaries and their contrast. If measurements are strongly skewed or have unusual values, a method based on a simple symmetric distribution may not describe uncertainty well. General statistical methods can address such features through transformations, robust approaches, or other models, but the registry does not say which method was used. It would not be appropriate to infer an analysis method from the displayed values alone.

How should missing analyses and event entries be handled?

Missing outcome data can affect a comparison if the probability of having a recorded outcome differs between groups or depends on participant characteristics or the outcome itself. Analysis populations also matter: an intention-to-treat analysis, for example, typically retains participants in their randomized groups, while other approaches may use a different set of observations. These are general considerations. The registry record does not report missing-data counts, reasons for missingness, an analysis population, or a missing-data strategy.

The adverse-event entries list zero participants at risk and zero affected for serious and other events in each arm. The deaths field is not reported in the registry record. Without information on event definitions, collection procedures, follow-up, and the population represented by those entries, the zeros cannot be interpreted as a complete demonstration of safety. The registry’s posted primary endpoint values and event entries should be considered alongside the substantial gaps in the reported analysis details.

10. Multiplicity, Missing Data and Analysis Populations

The registry names one primary outcome, cecal intubation time, and two secondary outcomes: patient comfort during the insertion phase and success rate of minimal-sedation colonoscopy. It does not report an analysis plan describing how tests across these outcomes were handled, whether any secondary outcome was designated as confirmatory, or whether an adjustment for multiple comparisons was planned. Multiplicity procedures and the rationale for them are therefore not reported in the registry record. No p-values are posted, so the record does not allow assessment of any multiplicity-adjusted or unadjusted significance claims.

Missing-data reporting is also limited. The registry provides arm counts alongside the primary endpoint summaries, but does not state how many randomized participants had an evaluable primary outcome, whether there were missing time measurements, or how any missing observations were handled. Reasons for missingness and sensitivity analyses are not reported in the registry record. The relationship between the listed enrollment and the arm-level outcome counts is not explained.

The analysis population is not described. The registry does not report whether participants were analyzed according to randomized assignment, whether any participants were excluded from analysis, or whether a per-protocol or other population was used. It also does not report a statistical analysis plan, interim analyses, adjustment for baseline characteristics, or the method used to estimate the confidence intervals. These are unknowns, not evidence that a particular approach was or was not used.

For adverse events, the registry entries list zero participants at risk and zero affected for serious and other events in both groups, while deaths are not reported in the registry record. No further details of follow-up or event ascertainment are reported. The absence of this information limits interpretation of both outcome completeness and event reporting.

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

The posted results describe cecal intubation time values of 6.9 minutes in the cap-assisted group and 7.4 minutes in the group using water immersion without a cap. Their 95% confidence intervals are 4.0 to 9.8 and 3.2 to 11.6, respectively. These are descriptive arm-level results. The registry record does not post a direct estimate of the difference between the randomized groups or an inferential test, so the reported values do not establish the statistical evidence for a comparative effect.

The values do not show that one approach is clinically preferable. The registry lists 20 % as the difference the investigators considered clinically relevant for planning, but does not report a comparison of the observed contrast with that threshold. No treatment recommendation follows from the arm summaries alone. The primary endpoint also addresses insertion time, not every feature of the procedure or the experience of participants.

Patient comfort during insertion and success rate of minimal-sedation colonoscopy are named as secondary outcomes, but their results are not reported in the registry record. The adverse-event entries are limited to zeros in fields for participants at risk and affected; deaths are not reported. Those entries do not give enough context to conclude that no adverse events occurred or to characterize the safety profile.

More broadly, this record does not establish whether the trial achieved its planned analysis, whether all randomized participants were included, or how missing data were managed. The sample-size target is a planning statement, not an observed measure of power or a guarantee of precision. The appropriate reading is therefore bounded: the record reports two arm-level primary-outcome summaries with confidence intervals, but leaves the direct statistical comparison and several important trial-analysis details unreported.

12. Why This Trial Matters Statistically

This trial illustrates why a randomized comparison is most informative when the result is reported as a direct contrast, not only as separate arm summaries. The registry reports cecal intubation time values and confidence intervals for each group, but not an estimate and interval for the difference between the groups. A reader can describe the observed arm summaries, yet cannot use them alone to quantify the uncertainty around the treatment contrast.

The study also highlights the importance of distinguishing design assumptions from outcome evidence. The investigators specified a clinically relevant difference of 20 % and a target of 93 subjects per arm, along with a two-tailed alfa 0.05 and beta 0.2. Those are planning assumptions. They do not show the precision achieved in the final comparison, especially when the comparative estimate and analysis are not reported.

Finally, the registry names patient comfort and success of minimal-sedation colonoscopy as secondary outcomes, but does not report their results. This matters because an intervention can be evaluated on more than one dimension, and the primary time measure does not answer every question about a procedure. Reporting the outcome definitions, analysis populations, missing-data handling, and comparative estimates would help readers distinguish what was measured from what remains uncertain. The record is a useful example of how registry entries can provide trial design and outcome summaries while leaving key analytical information unavailable.

13. 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 registry record gives limited information about eligibility and recruitment. It identifies colonoscopy as the condition and describes minimal-sedation colonoscopy, but does not report detailed inclusion or exclusion criteria, participant characteristics, or the recruitment process. These omissions make it difficult to judge how closely the enrolled population reflects other groups undergoing colonoscopy.

The record identifies the study as randomized and single-masked, but does not report how the random sequence was generated, whether allocation was concealed, or who was masked. It also does not describe adherence to the assigned procedure, any deviations, or how failures to reach the cecum were handled. These details are relevant to interpreting a time-to-cecum outcome and the integrity of the group comparison.

The primary outcome is reported with arm-level values and 95% confidence intervals, but without a direct comparative estimate, p-value, or analysis method. The registry does not specify whether the reported values are means or another summary. It also does not describe the analysis population, missing measurements, exclusions, or sensitivity analyses. The relationship between enrollment of 208 and the arm summaries of 98 participants each is not explained.

Results for both listed secondary outcomes are not reported in the registry record. Adverse-event entries list zero at risk and zero affected for serious and other events in each arm, while deaths are not reported. The record does not provide further information about event definitions, surveillance, or follow-up. The single-center setting is explicit, but the registry provides no additional details to assess how broadly the findings might apply. These limitations constrain interpretation of both the primary comparison and the wider clinical context.

14. Related Tutorials

15. Related Statistical Calculators

16. Sources

• ClinicalTrials.gov: Cap-assisted Water Immersion Versus Water Immersion Colonoscopy — NCT01547247.
• Registry record last updated 2015-10-23; status last verified 2015-10.
• Results first posted 2013-01-28.
• 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.

17. Record Summary

NCT01547247 is a completed, prospective, randomized, parallel-group, single-center trial sponsored by Vitkovice Hospital. It compared cap-assisted water immersion colonoscopy with water immersion colonoscopy without a cap. Both approaches used water immersion during insertion and room air insufflation during withdrawal. The registry reports enrollment of 208 and primary completion in 2012-05.

The primary endpoint was cecal intubation time, defined as the time from introduction of the colonoscope into the anus to reaching the cecum. Posted arm values are 6.9 minutes (95% CI 4.0 to 9.8) for cap-assisted colonoscopy and 7.4 minutes (95% CI 3.2 to 11.6) for water immersion colonoscopy without a cap. No comparative analysis is reported in the registry record.

The stated planning target was 93 subjects per arm, based on a clinically relevant difference of 20 %, two-tailed alfa 0.05, and beta 0.2. Patient comfort during insertion and success rate of minimal-sedation colonoscopy are listed as secondary outcomes, but their results are not reported in the registry record.