Gatorade/Miralax With or Without Bisacodyl Versus NuLytely for Colonoscopy Preparation: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Gatorade/Miralax With or Without Bisacodyl Versus NuLytely for Colonoscopy Preparation (NCT01063049), a randomized phase 4 study. The primary outcome is The Quality of the Colon Preparation Will be Graded Using the Boston Bowel Preparation Scale.

2. Clinical Question

3. Trial Design

The registry identifies this as a randomized, parallel-group phase 4 trial with single masking. The identity of the masked party and further details about how masking was implemented are not reported in the registry record. The recorded enrollment is 600. The listed outcome groups each have 200 participants, but these group counts do not establish how many participants contributed to every outcome or analysis.

The trial compared three preparation regimens. One group received NuLytely, described as 128 oz (1 gallon) from about 5 PM to 9 PM the night before colonoscopy. A second received Gatorade and Miralax with placebo: Miralax 51 g and placebo at 12 noon, followed by Gatorade 64 oz mixed with Miralax 255 g from about 5 PM to 9 PM. A third received Gatorade and Miralax with bisacodyl: Miralax 51 g and bisacodyl 10 mg at 12 noon, followed by the same stated evening mixture.

The recorded start was 2010-02, primary completion was 2011-02, and status is completed. The sponsor is Gastroenterology Services, Ltd. The registry labels the trial single-masked but does not report the masking procedure, the randomization method, the allocation-concealment approach, the trial sites, or the original statistical design assumptions. The primary outcome was assessed after colonoscopy. The registry also lists the Ottawa Scale as a secondary outcome.

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.

6. Primary Endpoint

The registry lists the primary outcome as The Quality of the Colon Preparation Will be Graded Using the Boston Bowel Preparation Scale, measured over After Colonoscopy.

The primary endpoint is the mean Boston Bowel Preparation Scale score after colonoscopy. The registry describes the scale as measuring colon cleanliness from 0 (very poor) to 9 (excellent). The score therefore gives a numerical summary of preparation quality, with higher values corresponding to cleaner preparation under the scale description in the registry.

A continuous score can be summarized by its mean and standard deviation. The mean describes the group’s average score, while the standard deviation describes the spread of scores among participants. Comparing group means addresses whether average scores differed, but does not describe every participant’s experience or the distribution of individual scores in full.

This endpoint is relevant to the stated study purpose because the registry asks whether the preparation methods do a better job cleaning out the colon before colonoscopy. The score is assessed after the procedure, as recorded for the outcome timeframe. The registry does not report a threshold defining an acceptable preparation, a minimally important difference, or how the scale was applied by assessors. Such details would help interpret the clinical importance of a difference in score, separate from its statistical uncertainty.

7. Results Posted in the Registry

• Nulytely: mean 7.86 versus 8.05 on control; difference -0.19 (95% CI -0.47 to 0.09), standardized effect d = -0.13; z-test p = 0.181.
• Gatorade/Miralax + Bisacodyl: mean 7.99 versus 8.05 on control; difference -0.06 (95% CI -0.32 to 0.20), standardized effect d = -0.04; z-test p = 0.656.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

The Ottawa Scale for Colonoscopy Preparation Will be Reported and Compared Among the 3 Groups to Allow for Comparisons to Some of the Older Literature

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Nulytely: mean 2.80 versus 2.58 on control; difference 0.22 (95% CI -0.24 to 0.68), standardized effect d = 0.09; z-test p = 0.351.
  • Gatorade/Miralax + Bisacodyl: mean 2.71 versus 2.58 on control; difference 0.13 (95% CI -0.35 to 0.61), standardized effect d = 0.05; z-test p = 0.599.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Nulytely and the control. The interval gives the range of effects that remain compatible with the data.
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Gatorade/Miralax + Bisacodyl and the control. The interval gives the range of effects that remain compatible with the data.

The Ottawa Scale is the secondary outcome listed in the registry. Its posted group means are close in numerical terms, and the reported unadjusted comparisons have confidence intervals that include zero. The overall pattern is therefore consistent with no clearly separated group averages on this secondary measure, while also retaining uncertainty about the size and direction of possible differences.

The primary and secondary outcome patterns are broadly aligned in that neither set of posted comparisons gives clear evidence of a difference between the placebo combination and either alternative regimen. Agreement across outcomes can be informative, but it does not make the measures interchangeable: they are different scales, and the registry does not provide enough detail to interpret the Ottawa Scale’s direction or a clinically important threshold.

The secondary results carry less weight for confirmatory conclusions because they are unadjusted and the registry does not report a multiplicity strategy. When several outcomes or comparisons are examined, the chance of finding an apparently notable result by chance can increase. Adjustment methods and prespecified outcome hierarchies can address that concern, but their use in this trial is not reported in the registry record. The secondary results are best treated as supportive descriptive evidence rather than as independent proof of a treatment difference.

The record says the Ottawa Scale would be reported and compared among the groups to allow comparison with older literature. It does not report details of the scale’s assessment, the analysis population, missing-data handling, or the analysis plan. The secondary findings therefore add context, but do not resolve the limitations in the primary-outcome interpretation.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• The Ottawa Scale for Colonoscopy Preparation Will be Reported and Compared Among the 3 Groups to Allow for Comparisons to Some of the Older Literature

9. Statistical Interpretation

10. Statistical Methods Explained

The primary outcome is continuous: it is a numerical score rather than a count of events or a yes-or-no outcome. The registry reports group means and standard deviations. A mean difference expresses the contrast between the average score in a comparison group and the average score in the reference group, in the score’s original units. Here the reference is Gatorade/Miralax with placebo. A negative estimate means the comparison group’s reported mean was lower; a positive estimate would mean it was higher. The sign alone does not establish a meaningful advantage.

A confidence interval gives a range of values compatible with the estimated contrast under the calculation’s assumptions. It communicates uncertainty around the point estimate rather than the range of individual participants’ scores. When an interval includes zero, the data do not distinguish the observed contrast from no difference at the interval’s confidence level. The registry does not state the confidence level or the inferential model used for its original analysis. The posted estimates include confidence intervals, but the registry lists no reported analyses.

The standard deviation is a measure of variation among individual scores within a group. It should not be confused with the standard error, which describes precision of an estimated mean. The posted comparison data include standard errors for the group means, as well as a pooled standard deviation and a standardized effect estimate. A standardized effect expresses the contrast relative to a measure of variability; it can help compare effects across scales, but it is less directly interpretable than the difference in Boston scale units. The registry does not report a threshold for a clinically important score difference.

The reported p-values are unadjusted. A p-value measures how surprising data at least as inconsistent with a specified null model would be if that model and its assumptions held. It is not the probability that the null hypothesis is true, and it does not quantify the probability that a regimen is effective. The registry does not report the trial’s original significance threshold or its planned model. The 0.05 significance level belongs to the separate sample-size planning illustration, not to a documented trial analysis plan. The p-values should therefore be read alongside the point estimates and confidence intervals, not as standalone conclusions.

Randomization can support fair comparisons by distributing known and unknown participant characteristics across assigned groups on average. That benefit depends on implementation and analysis, and the registry does not describe the randomization procedure or allocation concealment. The trial is labeled single-masked, but the record does not identify who was masked. These details matter because expectations or knowledge of assignment could influence some aspects of outcome assessment or reporting. The record does not report whether the scale assessors were masked.

General statistical note: over-dispersion matters most for outcomes whose variation exceeds the assumptions of a simple count model. It can make standard errors too small if ignored. The primary outcome is a continuous scale score, and the registry reports standard deviations; it does not report an over-dispersion assessment or a model that would require one. The record does not provide individual scores, so the distribution, skewness and potential influence of extreme scores cannot be assessed from the posted summaries alone.

The posted summaries allow straightforward descriptions of group means and unadjusted mean contrasts. They do not show whether an adjusted analysis, a model accounting for covariates, or another method was used by the trial investigators. The registry lists no reported analyses. It also does not state how missing outcome observations were handled, which analysis population was used, or whether participants were analyzed according to randomized assignment. Those omissions limit assessment of how the displayed summaries relate to the original analysis plan.

The secondary Ottawa Scale is also continuous and is reported as a mean and standard deviation. Its scale-specific interpretation and direction are not described in the record beyond its use for comparison with older literature. Its results should therefore be interpreted according to the reported estimates, without assuming a score direction or a clinical threshold not stated in the registry.

11. Confidence Intervals and Precision

Precision is reflected most directly by the confidence intervals around the mean differences. For NuLytely versus Gatorade/Miralax with placebo, the estimated primary-outcome difference is -0.19, with a confidence interval from -0.469 to 0.089. For Gatorade/Miralax with bisacodyl versus the same reference, the estimate is -0.06, with a confidence interval from -0.324 to 0.204. Each interval spans zero, so the posted data are compatible with no difference and with nonzero differences in either direction within the interval.

The intervals also show that the estimates are not exact. The point estimate is the single best estimate under the calculation, while the interval conveys uncertainty around it. Neither interval alone establishes whether any compatible difference would matter clinically. The registry does not state a minimally important difference for the Boston scale or a threshold for acceptable preparation, so statistical precision cannot be translated into a definitive clinical judgment.

The group standard deviations give context for the spread of individual scores, but they are not confidence intervals. The record reports standard deviations of 1.55 for NuLytely, 1.28 for Gatorade/Miralax with placebo, and 1.41 for Gatorade/Miralax with bisacodyl. Group means can be fairly close even when individual scores vary; the reported summaries do not reveal the full score distributions.

The registry does not state the confidence level or the method used to form its intervals. It also does not report missing-data handling, the analysis population, or the original analysis plan. These factors can affect precision and interpretation, so the intervals should be understood as uncertainty measures attached to the posted comparisons, not as a complete account of all uncertainty in the trial.

12. 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 are illustrations calculated from the observed effect, not the trial’s original design assumptions. The stated planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. Each planning scenario uses the stated fraction of the observed effect as the effect to detect.

The 80% power column gives the number of participants per arm that the planning calculation estimates would be needed for an 80% chance of detecting the specified effect under those assumptions. The 90% power column gives the corresponding number for a 90% chance. Power is a property of a planned study under specified assumptions; it does not state the probability that the observed result is true or that a particular conclusion is correct.

Rows using 100% of the observed effect plan for the effect at its observed size. Rows using 75% or 50% plan for smaller effects relative to that observed estimate. Smaller effects are harder to distinguish from random variation, so the planning figures increase as the target effect becomes smaller. Because the observed effect is uncertain, using it as the basis for planning is only an illustration and is not a substitute for a prespecified target based on scientific and clinical judgment.

This is not observed power. The registry does not report the trial’s original sample-size justification or assumptions. The planning values should not be read as evidence that the completed trial was designed to detect the observed contrasts, or as a retrospective measure of whether its results are reliable.

13. 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, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -0.190; pooled standard deviation σ = 1.421.
2. n = 2 × (1.96 + 0.842)² × 1.421² / -0.190² = 878.6, rounded up to 879 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
delta <- -0.19                      # observed difference in means
sigma <- 1.421425340987                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^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 (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(1063049)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 879 (80% power), 1,177 (90% power)
 75% of observed effect: n per arm = 1,562 (80% power), 2,091 (90% power)
 50% of observed effect: n per arm = 3,515 (80% power), 4,705 (90% power)
power.t.test: 879.5 
Simulated power at n = 879 per arm: 0.799 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-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.

14. Multiplicity, Missing Data and Analysis Populations

The record includes a primary outcome, a secondary outcome and multiple group comparisons. It does not report a statistical plan for controlling multiplicity, such as an adjustment across comparisons or a prespecified hierarchy for interpreting outcomes. Since the posted comparison p-values are unadjusted, they should not be treated as if they automatically account for the number of outcomes or comparisons examined. The registry does not report whether multiplicity was addressed in the trial’s original analysis.

Missing-data handling is not reported in the registry record. The outcome summaries list 200 participants in each group, but those counts alone do not establish whether every randomized participant had an outcome measurement or whether the same analysis population was used for all outcomes. The record does not give reasons for missing observations, describe any imputation method, or report sensitivity analyses. These omissions make it difficult to evaluate whether incomplete outcome data could have influenced the group comparisons.

The analysis population is also not reported. The record does not say whether the investigators analyzed participants according to randomized assignment, restricted analysis to participants who completed the preparation and colonoscopy, or used another definition. It also does not describe exclusions or protocol deviations. Without this information, the posted group summaries cannot be linked confidently to a named analysis population.

The registry identifies randomization and single masking, but further details are absent. The method of random sequence generation, allocation concealment, identity of the masked party, and masking of outcome assessors are not reported. The original statistical model, covariate adjustment, and trial-specific significance threshold are likewise not reported in the registry record. These gaps do not invalidate the descriptive results, but they limit evaluation of the analysis process and the strength of confirmatory claims.

15. 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 0.5% reporting threshold.

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: post-polypectomy bleed (0.5%).

The serious adverse event figures list no serious events for NuLytely, one serious event for Gatorade/Miralax with placebo, and no serious events for Gatorade/Miralax with bisacodyl. The listed serious event term is post-polypectomy bleed, reported as 0.5%. Other adverse events are recorded as none in each group. Deaths are not reported in the registry record.

These counts describe events recorded in the registry, not a complete assessment of comparative safety. The record does not provide event narratives, timing, severity details beyond the serious classification, attribution to a preparation, or methods for collecting and adjudicating events. It also does not report a statistical comparison of adverse event rates. A count of no recorded events in a group does not show that the risk is absent, and the single listed serious event does not by itself establish a difference between regimens. The figures should be read as sparse descriptive reporting, not as proof of safety or harm.

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

The posted primary results show similar group average Boston Bowel Preparation Scale scores, with estimated mean differences close to zero when NuLytely and Gatorade/Miralax with bisacodyl are compared with Gatorade/Miralax with placebo. The confidence intervals include zero and allow a range of possible differences. The secondary outcome also does not show a clearly separated pattern in its unadjusted comparisons. These are descriptions of the recorded results, not a demonstration that the regimens are equivalent.

The results do not establish that any regimen is superior, nor do they prove that there is no meaningful difference. The registry does not report a margin for equivalence or non-inferiority, a clinical importance threshold for the primary scale, or a prespecified analysis plan that would support such conclusions. A nonsignificant unadjusted p-value does not prove equality; it indicates that the data do not provide strong evidence against the null model under the calculation used.

The registry’s stated purpose also includes patient acceptability, but an acceptability result is not reported in the posted outcomes. Consequently, the cleanliness scores cannot answer that aspect of the study question. The safety record contains sparse event counts and is not a basis for concluding that one preparation is safer.

General interpretation requires attention to the study context and methods, including who was enrolled, how outcomes were assessed, missing data, masking and the analysis population. Several of these details are not reported in the registry record. The posted summaries can inform a comparison of average scores, but cannot replace information about individual variability, patient experience, or the trial’s full analysis. No treatment decision follows from these statistics alone.

17. Why This Trial Matters Statistically

This trial is statistically useful as an example of why a point estimate, its uncertainty and the study question should be read together. The mean differences for the primary outcome are close to zero, but their confidence intervals extend across zero and include values in both directions. That combination differs from proof of no difference: it describes estimates that are uncertain enough to remain compatible with multiple possibilities.

It also illustrates the distinction between statistical and clinical importance. A difference can be estimated precisely yet be too small to matter, or an estimate can be uncertain enough that meaningful differences remain plausible. The registry does not give a clinically important threshold for the Boston scale, so the score contrasts cannot be classified against such a benchmark from the record alone.

The planning illustrations show why sample-size expectations depend on the target effect. Planning for a smaller effect calls for more participants per arm under the stated assumptions. These calculations use the observed effect and are not the trial’s original design justification, so they should not be confused with an assessment of the trial’s original adequacy or its observed power.

Finally, the record demonstrates the importance of transparent reporting. Details about multiplicity, missing data, analysis populations, masking implementation and the original statistical plan are not reported. Such information helps readers assess whether a numerical comparison is confirmatory, exploratory or primarily descriptive. The posted estimates remain useful, but their interpretation should reflect both the results and the limits of the registry record.

18. 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 limitations specific to this trial arise from details not reported in the registry record. Participant characteristics and eligibility criteria are not described in the registry entries, limiting assessment of whom the results represent. The setting and number of trial sites are also not reported. The registry describes single masking but does not state who was masked, how masking was maintained, or whether the colonoscopy assessors were masked to group assignment.

The original statistical analysis plan, sample-size justification and significance threshold are not reported. The registry lists no reported analyses, and the posted comparisons are unadjusted. It is therefore unclear whether these calculations correspond to a prespecified trial analysis, whether additional comparisons were planned, or how multiplicity was considered. Missing-data procedures, analysis populations and handling of protocol deviations are also not reported.

The results are group-level summaries rather than individual participant data. The score distributions and possible outliers cannot be evaluated from the reported means and standard deviations alone. The registry does not state a clinically important difference or acceptable-score threshold for the primary scale. It also does not provide details about outcome assessor training or the scoring process. For the Ottawa Scale, the record does not give scale interpretation details beyond its purpose for comparison with older literature.

The stated study purpose includes patient acceptability, but the posted outcomes do not include an acceptability result. Safety reporting is limited to the listed event counts and does not include narratives or a statistical comparison. These limitations restrict conclusions about patient experience, comparative safety and how closely the numerical results reflect the full trial analysis.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Gatorade/Miralax With or Without Bisacodyl Versus NuLytely for Colonoscopy Preparation — NCT01063049.
• Registry record last updated 2013-11-18; status last verified 2013-11.
• Results first posted 2013-11-18.
• 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.

22. Record Summary

The registry record describes NCT01063049 as a completed, randomized, parallel-group, single-masked phase 4 trial sponsored by Gastroenterology Services, Ltd. Its recorded enrollment is 600. The study compared NuLytely with Gatorade/Miralax plus placebo and Gatorade/Miralax plus bisacodyl for colonoscopy preparation.

The primary outcome was mean Boston Bowel Preparation Scale score after colonoscopy. The posted group means were 7.86 for NuLytely, 8.05 for Gatorade/Miralax with placebo, and 7.99 for Gatorade/Miralax with bisacodyl. Both unadjusted comparison intervals include zero. The Ottawa Scale is the listed secondary outcome, and serious adverse event counts are sparse.

The registry does not report the trial’s original statistical plan, missing-data procedures, analysis population, multiplicity approach, or patient acceptability results. The posted comparisons describe average outcomes but do not establish equivalence or a clinically important difference.