Bowel Preparation for Colonoscopy in Children: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Bowel Preparation for Colonoscopy in Children (NCT01140295), a randomized phase 4 study. The primary outcome is Efficacy of Colon Preparation.

2. Clinical Question

The study’s stated objective was to determine whether Miralax resulted in a more efficacious preparation than senna for pediatric colonoscopy. The primary outcome was recorded as a percentage of patients, assessed once one day after completion of colonoscopy preparation. The registry reports 88% with excellent or good preparation in the Miralax group and 28% in the senna group.

These results address the recorded preparation-quality outcome in this trial. They do not, by themselves, answer broader questions about every aspect of colonoscopy preparation or establish how results would apply to children outside the trial population. Eligibility details, the reason the trial was terminated, and further information about the patients are not reported in the registry record.

3. Trial Design

The registry describes a randomized, parallel-group trial with single masking. Its official title characterizes it as prospective and investigator-blinded. The record identifies two preparation groups: Miralax and senna. It lists the study as Phase 4 and gives enrollment as 33.

The study start is recorded as 2010-09 and primary completion as 2011-05. Its status is TERMINATED. The reason for termination and any consequences for recruitment or follow-up are not reported in the registry record. The record does not provide further details about the randomization procedure, allocation concealment, who was masked beyond the investigator-blinded description, or whether masking was maintained.

The primary endpoint was the percentage of patients with excellent or good colonoscopy preparation, measured once one day after completion of preparation. The registry also lists the proportion of patients with abnormal electrolyte levels as a secondary outcome. Although two outcome measures are recorded, only one secondary outcome is posted in the outcome information. A result for abnormal electrolyte levels is not reported in the registry record.

The posted outcome counts are 17 for Miralax and 16 for senna. The record does not describe a separate analysis population, whether every enrolled participant contributed to the outcome, or how missing observations were handled. The original sample-size assumptions and the trial’s own statistical analysis plan are not reported in the registry record. The planning figures available alongside the posted results are illustrations based on the observed effect, not evidence of the assumptions used to design this trial.

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: 365 patients were screened. 98 were eligible according to inclusion/exclusion criteria. 41 declined participation. criteria. Of the 57 eligible patients 33 were enrolled when the study was prematurely terminated.

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 Efficacy of Colon Preparation, measured over The outcome measure will be assessed once one day after the completion of colonoscopy preparation.

The primary endpoint is the percentage of patients whose colonoscopy preparation was rated excellent or good. Ratings are based on a validated colon cleanliness scale identified in the record as the Aronchik scale, which has five levels. The registry describes levels 1 and 2 as excellent or good and routinely recognized as adequate for successful completion of colonoscopy. Levels 3 through 5 indicate incomplete or poor preparation and are associated with significant residual stool at colonoscopy.

This endpoint reduces the scale to a binary outcome: adequate preparation, defined as excellent or good, versus the other listed levels. Such a summary makes the proportion meeting the specified adequacy criterion straightforward to compare between groups. It also means that the posted percentage does not show the distribution across all five cleanliness levels; the registry record does not report those level-by-level results.

The outcome was assessed once, one day after completion of colonoscopy preparation. The record does not describe who rated cleanliness, whether ratings were independently assessed, or how disagreements were resolved. Although the official title specifies investigator blinding, details about blinding for this assessment are not reported in the registry record.

7. Results Posted in the Registry

• 2, Senna: 25.0% (4/16) versus 88.2% (15/17) on control; risk difference -63.2 percentage points (95% CI -89.4 to -37.1), risk ratio 0.28 (0.12–0.67); unadjusted two-proportion z-test p = <0.001.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is binary because each patient is classified according to whether preparation was excellent or good, rather than by the individual cleanliness rating across all five Aronchik levels. The reported percentages are therefore proportions meeting a defined criterion. General: binary outcomes can be summarized by the proportion in each group and compared with measures such as a risk difference, risk ratio, or odds ratio. Each measure describes a different scale for the same underlying group contrast.

What does the risk difference mean?

The posted risk difference is -0.632 for senna relative to Miralax. A risk difference subtracts the event proportion in the reference group from the event proportion in the comparison group. Here the event is excellent or good preparation. The minus sign indicates that the observed proportion was lower in the senna group. Risk differences use an absolute scale, so they describe the change in the proportion meeting the endpoint rather than a relative change. The associated confidence interval is -0.894 to -0.371.

How do the relative measures differ?

The risk ratio is 0.283, with a confidence interval from 0.119 to 0.674. A risk ratio compares the event proportions between groups; a value below one indicates a smaller observed proportion in the senna group relative to Miralax. The odds ratio is 0.044, with a confidence interval from 0.007 to 0.285. Odds are not the same as probabilities. When outcomes are common, an odds ratio can differ considerably in numerical appearance from a risk ratio, so these measures should not be treated as interchangeable. Neither relative measure adds a separate outcome to the trial’s findings.

What does the p-value tell us?

The unadjusted p-value is <0.001. General: a p-value describes how incompatible the observed data are with a specified null model, assuming that model and the analysis assumptions hold. It is not the probability that the null model is correct, and it does not express the size or practical importance of an effect. The record identifies this value as unadjusted. A detailed statistical plan, including any prespecified adjustment approach, is not reported in the registry record.

What is the role of a confidence interval?

A confidence interval communicates the precision of an estimate under the method used to construct it. It gives a range of values that are reasonably compatible with the observed data and the model assumptions. It is not a range containing a fixed percentage of individual patient outcomes, nor is it a direct probability statement about the true effect. Wider intervals indicate less precision than narrower intervals. For this trial, the confidence interval for the risk difference includes estimates of different magnitudes, while staying below zero.

What can be inferred from the posted counts?

The endpoint counts are 15 of 17 in the Miralax group and 4 of 16 in the senna group. The posted percentages, 88% and 28%, are rounded summaries. The comparison statistics are unadjusted calculations based on the reported group results. They should be read alongside the registry’s outcome definitions and the limitations in reporting. General: with a binary endpoint, a change in the classification of an individual can affect the estimated proportion, especially when group sizes are limited. The registry does not report how missing measurements, if any, were handled.

General: over-dispersion is a concern in some models when variability exceeds what the model assumes. This trial’s primary endpoint is reported as a binary percentage, and no over-dispersion estimate or model-based adjustment is reported in the registry record. There is therefore no basis in the posted information for attributing the comparison to a model that accounts for over-dispersion.

The registry reports zero analysis records, while also posting the group outcomes and a comparison. The statistical plan and any other analyses are not reported in the registry record. The comparison is consequently best understood as an unadjusted summary of the posted outcome data, not as evidence that every element of the trial’s intended analysis can be reconstructed.

10. Confidence Intervals and Precision

The risk-difference estimate for senna relative to Miralax is -0.632, with a 95% confidence interval from -0.894 to -0.371. This interval communicates uncertainty about the size of the contrast: values across a substantial range remain compatible with the data under the method used. Because the interval lies below zero, its range is consistent with a lower proportion meeting the endpoint in the senna group than in the Miralax group. It does not indicate that the magnitude is known precisely.

The relative estimates are also uncertain. The reported risk ratio is 0.283, with a confidence interval from 0.119 to 0.674; the odds ratio is 0.044, with a confidence interval from 0.007 to 0.285. These intervals describe uncertainty on different scales and should not be compared as though their numerical widths had the same meaning.

General: a confidence interval reflects both the observed data and the statistical method used to calculate it. It does not account automatically for limitations such as unreported missing-data handling, incomplete analysis-plan details, or uncertainty about generalizability. The registry does not report confidence intervals for the individual group percentages. The relatively limited group sizes and the broad range of the risk-difference interval are important context when interpreting the apparent separation in the observed percentages.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not total events. They illustrate sample sizes under the listed planning assumptions: two-sided significance level 0.05, equal allocation between two arms, and a normal approximation. The effect to detect is specified as a fraction of the observed effect. The original design assumptions for this trial, including its planned sample size justification, are not reported in the registry record.

The 80% power column gives the illustrative number of participants per arm for a design with 80% power under those assumptions and the selected effect size. The 90% power column gives the corresponding number per arm for 90% power. In general, higher target power requires more participants when other assumptions are held constant. The listed rows show planning for 100%, 75%, and 50% of the observed effect. Smaller effects need more participants to detect than larger effects under the same assumptions.

These are planning illustrations based on the observed effect, not observed power. They do not show that the completed trial had a particular probability of detecting an effect, and they are not evidence of the sample size originally chosen by the investigators. The registry does not report whether the trial’s original design used the same significance level, allocation, approximation, or effect assumptions. The curve should be interpreted on the same planning basis as the listed figures, rather than as a reconstruction of the trial’s protocol.

12. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.882; treatment proportion p₁ = 0.250; average p̄ = 0.566.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.7009 = 1.3737.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.5397 = 0.4542.
4. n = (1.3737 + 0.4542)² / (-0.6324)² = 8.4, rounded up to 9 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
p0 <- 0.882352941176471                          # control proportion
p1 <- 0.25                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(1140295)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 9 (80% power), 11 (90% power)
 75% of observed effect: n per arm = 15 (80% power), 20 (90% power)
 50% of observed effect: n per arm = 31 (80% power), 40 (90% power)
power.prop.test: 8.4 
Simulated power at n = 9 per arm: 0.836 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Multiplicity, Missing Data and Analysis Populations

The registry lists a primary outcome of excellent or good colonoscopy preparation and identifies the proportion of patients with abnormal electrolyte levels as a secondary outcome. It also records two outcome measures, while one secondary outcome is posted. A result for abnormal electrolyte levels is not reported in the registry record. The analysis-record count is zero, although group results and a comparison are posted for the primary outcome.

The statistical analysis plan, the number of planned comparisons, and any procedures for handling multiple outcomes or repeated testing are not reported in the registry record. General: when multiple outcomes or comparisons are examined, the chance of at least one nominally small p-value can increase if no adjustment or prespecified interpretation is used. The available information does not establish whether multiplicity was considered in the original analysis. The posted p-value is identified as unadjusted, so it should not be read as a multiplicity-adjusted result.

The registry does not report the number of participants with missing primary-outcome data, how missing data were handled, or whether any imputation was used. It also does not state the analysis population, such as whether results were analyzed according to randomized assignment or another rule. The group outcome counts and at-risk counts are posted, but they do not resolve these reporting gaps.

General: missing-data methods and analysis-population definitions can affect how a trial estimate should be interpreted, because they determine which observations contribute and how incomplete records are treated. Without these details, it is not possible to assess the impact of missingness or establish whether the posted comparison follows an intention-to-treat approach. The registry does not report an analysis plan that would clarify these matters.

14. 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 0% reporting threshold.

The adverse-event record lists 0 serious adverse events among 17 patients at risk in the Miralax group and 0 among 16 at risk in the senna group. It also lists 0 other adverse events among 17 at risk in the Miralax group and 0 among 16 at risk in the senna group. No serious adverse-event terms are listed.

These are the counts recorded in the registry, not proof that an event could not occur. The record does not describe the adverse-event collection procedures, observation duration, or completeness of reporting. Death counts are not reported in the registry record. The safety figures should be interpreted as the posted event counts for this trial, not as a complete estimate of risk or as a comparison capable of establishing safety differences.

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

The posted primary outcome shows a higher observed percentage of excellent or good preparation in the Miralax group than in the senna group: 88% versus 28%. The unadjusted risk difference for senna relative to Miralax is -0.632, with a 95% confidence interval from -0.894 to -0.371, and the unadjusted p-value is <0.001. These results describe the recorded outcome in the randomized groups and indicate that the observed difference is unlikely to be explained by sampling variation alone under the comparison’s assumptions.

The result does not establish the size of the difference with high precision: the confidence interval covers a range of effect magnitudes. Nor does it show the full distribution across the five Aronchik cleanliness levels, because the posted primary endpoint groups excellent and good ratings together and contrasts them with other levels. The record does not report the secondary electrolyte outcome.

The trial was terminated, and the reason is not reported in the registry record. The available information also does not describe missing-data handling, analysis populations, details of randomization, or the statistical plan. These gaps matter when judging how completely the posted comparison represents the intended trial analysis. The record’s safety counts report no serious or other adverse events in either group, but the information provided does not establish the completeness or duration of safety monitoring.

The finding is specific to this trial’s recorded pediatric colonoscopy-preparation endpoint and should not be extended automatically to other populations, settings, or outcomes. It does not settle every question about preparation quality or safety, and it is not medical advice. Its statistical meaning is a marked difference in the observed proportions, accompanied by uncertainty and limitations in registry reporting.

16. Why This Trial Matters Statistically

This trial illustrates how a binary endpoint can make a clinically defined threshold easy to compare: the outcome distinguishes excellent or good preparation from less adequate categories. The percentage meeting that threshold provides a direct summary, while the risk difference expresses the absolute contrast between groups. Reporting the counts alongside percentages helps readers understand what observations underlie the summaries.

It also shows why effect estimates and precision should be considered together. The posted percentages differ substantially, and the unadjusted p-value is <0.001, but the confidence interval still spans a range of possible risk differences. A small p-value does not make an estimate precise or resolve uncertainty about generalizability. Alternative scales, such as risk ratio and odds ratio, describe the same comparison differently and should be interpreted according to their definitions.

The record’s reporting gaps are statistically important. It identifies termination status, but not the reason; lists a secondary outcome without a posted result; and does not report the original sample-size justification, missing-data approach, analysis population, or complete statistical plan. Such information is needed to assess whether the available comparison reflects all planned analyses and how robust it may be to incomplete observations or analysis choices.

Finally, the sample-size illustrations demonstrate the dependence of planning needs on the effect targeted and the assumed power. They are not evidence about the completed study’s power or its original design. Keeping planning calculations separate from observed results prevents a retrospective illustration from being mistaken for a prospective trial decision.

17. 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.
• Participant counts were reconstructed from posted percentages and arm sizes, so small rounding differences are possible.

The registry marks the study TERMINATED, but does not report the reason or describe how termination affected enrollment, follow-up, or outcome availability. The record gives enrollment as 33 and posts group outcome counts, but does not provide eligibility criteria, participant characteristics, or the analysis population. Generalizability beyond the trial population therefore cannot be assessed from the registry information.

Further design details are unavailable. The trial is described as randomized, parallel, and single-masked, and the official title says investigator-blinded, but the registry does not describe the randomization method, allocation concealment, who was masked, or masking implementation. The outcome uses a validated scale, but the record does not identify the assessor or explain how outcome ratings were determined.

The primary outcome is summarized as a binary percentage rather than a distribution across all five scale levels. The secondary electrolyte outcome has no posted result. Missing-data handling, the statistical analysis plan, and the original sample-size assumptions are not reported in the registry record. The adverse-event record lists zero events but does not describe monitoring duration or completeness; death counts are not reported. These limitations affect interpretation of both the efficacy comparison and the safety summary.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Bowel Preparation for Colonoscopy in Children — NCT01140295.
• Registry record last updated 2013-04-12; status last verified 2013-04.
• Results first posted 2013-04-12.
• 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.

21. Record Summary

NCT01140295 is a Phase 4 randomized, parallel-group trial titled Bowel Preparation for Colonoscopy in Children. Its official title describes a prospective, investigator-blinded comparison of polyethylene glycol powder solution and senna. The record lists enrollment of 33, start in 2010-09, primary completion in 2011-05, and status TERMINATED.

The primary outcome was the percentage with excellent or good colonoscopy preparation, assessed one day after completion of preparation. The registry reports 88% for Miralax and 28% for senna, with an unadjusted risk difference of -0.632 for senna relative to Miralax and a 95% confidence interval from -0.894 to -0.371. The unadjusted p-value is <0.001. The reason for termination, the secondary electrolyte result, missing-data handling, and the trial’s original design assumptions are not reported in the registry record.