Left Lateral Position Versus Supine Position in Colonoscopy: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Left Lateral Position Versus Supine Position in Colonoscopy (NCT06664762), a randomized na study. The primary outcome is Time to Cecal Intubation..

2. Clinical Question

3. Trial Design

The registry describes a completed, multicenter, single-blind, randomized clinical trial using a parallel-group design. The study compares two positions during colonoscopy: left lateral and supine. The reported enrollment is 144, with 72 participants assigned to each position for the primary outcome. The sponsor is Hospital Civil de Guadalajara. The study start date is 2024-08-27, and the primary completion date is 2025-07-30.

Randomization means that assignment to the two positions was intended to be based on chance rather than on a participant characteristic or clinical judgment. A parallel-group design means that the two sets of participants are compared according to their assigned position rather than each participant undergoing both positions as a crossover. These are general descriptions of the design; allocation concealment, the randomization procedure, and whether the analysis followed assigned position are not reported in the registry record.

The study is described as single-blind, but the record does not identify who was blinded or how blinding was maintained. Since the positions are different and applied during a procedure, the practical details of blinding would be relevant to interpreting measurement and conduct, but they are not reported in the registry record. The arm descriptions do not add procedural detail.

The registry lists time to cecal intubation as the primary outcome and the number of participants with at least one adenoma detected during colonoscopy as a secondary outcome. It lists two outcome measures and no reported analyses. The original sample-size justification, the planned statistical methods, the analysis populations, and any interim analyses are not reported in the registry record. The enrollment figure describes the study size; it does not by itself establish that the study was designed to detect a particular difference.

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: 150 patients were screened. Six did not meet eligibility criteria or declined participation. A total of 144 provided informed consent and were randomized 1:1 to start colonoscopy in left lateral decubitus or supine position.

Overall Study

Analysis population for the primary outcome, as defined in the registry: A total of 144 patients were included: 72 in the supine position and 72 in the lateral decubitus position.

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: Eligible patients, according to established guidelines, were scheduled for colonoscopy and assigned a randomized number.

6. Primary Endpoint

The registry lists the primary outcome as Time to Cecal Intubation., measured over 4-10 minutes, which is approximately 240-600 seconds.

The primary endpoint is time to cecal intubation, measured in seconds. It is defined as the time from insertion to reaching the cecum, regardless of the position used for colonoscopy. The registry gives a timeframe of 4-10 minutes, described as approximately 240-600 seconds. It summarizes the outcome using a mean and standard deviation for each group.

Time to cecal intubation is a continuous measure: it can take a range of values rather than being limited to categories such as yes or no. The mean describes the average time in a group, while the standard deviation describes the spread of individual times around that average. As a general statistical point, a timing measure can be useful for comparing procedural duration across groups, but its interpretation depends on how consistently it is measured and on the clinical and procedural context. The registry does not give further details about timing procedures, assessor training, or how unusual or incomplete measurements were handled.

The posted group means are 310.0 seconds for the left lateral position and 306.0 seconds for the supine position. The corresponding standard deviations are 332.0 and 305.0 seconds. The comparison is a difference in means, expressed as supine minus left lateral. A mean difference describes the contrast in group averages; it does not show the full distribution of individual times or establish that every participant experienced a similar duration. The registry does not state a threshold defining a clinically important difference in this endpoint.

7. Results Posted in the Registry

• Supine Position During Colonoscopy: mean 306.00 versus 310.00 on control; difference -4.00 (95% CI -108.13 to 100.13), standardized effect d = -0.01; z-test p = 0.940.

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.

Number of Participants With at Least One Adenoma Detected During Colonoscopy

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Supine Position During Colonoscopy: 41.7% (30/72) versus 30.6% (22/72) on control; risk difference 11.1 percentage points (95% CI -4.5 to 26.7), risk ratio 1.36 (0.88–2.12); unadjusted two-proportion z-test p = 0.165.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Supine Position During Colonoscopy and the control. The interval gives the range of effects that remain compatible with the data.

The registry lists one secondary outcome: whether a participant had at least one adenoma detected during colonoscopy. The observed counts favor a higher detection frequency in the supine group, while the unadjusted interval for the group contrast includes no difference and permits effects in either direction. Thus, the secondary result has a directional pattern but remains uncertain. It does not provide a definitive contrast between positions.

This secondary measure is related to the primary result because both outcomes concern the same colonoscopy procedure and are compared across the same randomized groups. They address different questions, however. Time to cecal intubation concerns procedural timing, whereas adenoma detection concerns whether at least one adenoma was recorded. A pattern in one outcome does not determine what should be concluded about the other, and the secondary endpoint cannot resolve the imprecision in the primary timing comparison.

Unadjusted secondary results generally carry less weight than a prespecified primary analysis because they may be one of multiple opportunities to observe a seemingly notable pattern. When several outcomes or comparisons are considered, the chance of finding an apparently unusual result by chance can increase. A multiplicity plan can clarify how such testing is handled, but one is not reported in the registry record. The record also reports no analyses, so it is unclear whether the displayed secondary comparison was part of a prespecified analysis strategy or whether any other secondary analyses were planned.

The secondary outcome should therefore be interpreted as descriptive and exploratory in the context of the posted information. Its direction can motivate further study, but the uncertainty and lack of reported multiplicity procedures mean it should not be treated as confirmatory evidence. No additional secondary endpoints are listed in the registry record.

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

• Number of Participants With at Least One Adenoma Detected During Colonoscopy

9. Statistical Interpretation

10. Statistical Methods Explained

The primary endpoint is summarized by a mean and standard deviation in each randomized group. The mean is the arithmetic average of the recorded times. The standard deviation describes the typical spread of individual values around the group mean; it is not the uncertainty of the estimated mean difference. In this study, the posted standard deviations are 332.0 seconds for the left lateral group and 305.0 seconds for the supine group. Those figures describe within-group variability, whereas the interval for the comparison describes uncertainty in the contrast between group means.

The displayed primary comparison is a mean difference, calculated in the direction supine minus left lateral. Its estimate is -4.0 seconds. A negative value means that the posted supine-group mean is lower than the posted left lateral-group mean. The interval, from -108.1 to 100.1 seconds, presents uncertainty around this contrast. An interval that includes zero is compatible with no difference in group means, but it also includes nonzero values in both directions. It does not establish that the true difference is exactly zero.

The accompanying unadjusted p-value is 0.94. In general, a p-value measures how unusual data at least as discrepant as those observed would be under a specified null model and its assumptions. It is not the probability that the null hypothesis is true, nor does it describe the size or clinical importance of an effect. The registry reports no analyses, so the statistical test and its detailed assumptions are not reported in the registry record. The comparison should therefore be read as a summary-based, unadjusted estimate rather than as evidence that a particular model or covariate adjustment was used.

The comparison also includes a pooled standard deviation of 318.8 seconds and group standard errors of 39.13 and 35.94 seconds. A standard error describes the sampling uncertainty of an estimated quantity, in contrast to a standard deviation, which describes variation among observations. The registry record does not state how these quantities were used in the sponsor's analysis, and it does not report an analysis method or adjustment set. They provide context for the summary comparison but do not resolve questions about the underlying distribution of times or data handling.

For the secondary outcome, each participant is classified according to whether at least one adenoma was detected. The group counts are 22 and 30 among 72 participants in each group. A risk is the proportion of participants meeting that binary outcome within a group. The risk difference is the difference between those proportions, expressed as supine minus left lateral. Its estimate is 0.111, with an interval from -0.045 to 0.267. The interval includes zero, so the posted summary does not precisely distinguish a positive difference from no difference or a difference in the opposite direction.

The secondary comparison also reports a risk ratio of 1.364, with an interval from 0.876 to 2.123, and an odds ratio of 1.623, with an interval from 0.817 to 3.224. These are alternative ways to describe the association between group and the binary outcome. A risk ratio compares the outcome risks directly; an odds ratio compares the odds. They are not interchangeable measures, and the odds ratio can be harder to interpret as a difference in probability. In this case, each interval spans the value corresponding to no association for its measure. These summaries are unadjusted, and no reported analyses clarify whether any other methods were used.

The registry's lack of reported analyses is an important limitation when interpreting all inferential statistics. The record does not state whether the primary comparison was prespecified in the same form as displayed, which test was used, whether assumptions were checked, or how missing or extreme observations were handled. It also does not report the analysis population or whether participants were analyzed according to randomized assignment. Those omissions do not invalidate the posted descriptive values, but they limit assessment of the inferential procedure and reproducibility.

Why does variation matter?

As a general statistical point, high variation among observations makes it more difficult to distinguish a group difference from random variation. The posted timing standard deviations are large compared with the estimated mean contrast. A wide interval is consistent with that limited precision. The group means alone would conceal this variability, which is why the standard deviations and interval matter for interpretation. However, summary values cannot reveal whether the spread is due to a broad, fairly regular distribution or a small number of unusually long times.

What does an unadjusted result mean?

An unadjusted comparison contrasts the groups without accounting for additional measured variables in the reported estimate. Randomization is intended to balance prognostic factors on average, but a small study can still have chance imbalances. Whether adjustment was planned or performed is not reported in the registry record. The p-values are explicitly unadjusted; the record does not give adjusted estimates. General statistical practice treats adjustment decisions as part of the analysis plan, not as a way to select whichever result appears most favorable after seeing the data.

What can summary statistics establish?

Group summaries can describe the posted results and support a comparison of averages or proportions. They cannot by themselves show individual trajectories, data quality, adherence to assigned position, or the exact analysis population. Nor do they establish whether a difference is clinically important. General statistical interpretation considers the estimate, its precision, the design, the prespecified question, and the quality and completeness of measurement together. The original statistical plan, clinically important thresholds, and details of data handling are not reported in the registry record.

11. Confidence Intervals and Precision

Precision concerns how narrowly the data locate the group contrast. For time to cecal intubation, the estimated mean difference is -4.0 seconds, and the interval runs from -108.1 to 100.1 seconds. This span is wide relative to the point estimate. It indicates that the posted data are compatible with a range of differences, including values favoring either position and values close to no difference. The estimate is therefore not precise enough to settle the direction or size of a potentially relevant difference.

A confidence interval is a statistical range produced by a method intended to have a stated long-run coverage under its assumptions. It is not a guarantee that the true value lies in this particular interval, and it does not give a probability distribution for the effect. The confidence level is not reported in the registry record, so no confidence percentage should be attributed to these intervals. Their width remains informative as a description of the uncertainty in the posted comparisons.

For adenoma detection, the risk-difference interval extends from -0.045 to 0.267, also including no difference and values on either side. The alternative risk-ratio and odds-ratio intervals likewise include their respective no-association values. These intervals do not establish that the groups have the same detection rate; they show that the observed estimates are not sharply separated from no difference under the posted comparisons.

Precision depends on the amount of information in the data, variability, and the analysis method. The primary endpoint has 72 participants per group, and its standard deviations are 332.0 and 305.0 seconds. The registry does not provide raw observations, missingness details, or analysis methods that would allow a fuller assessment of why the intervals have their observed widths. A narrow estimate is not the same as a clinically meaningful one, and a broad interval does not prove that an important difference exists. It means the result remains uncertain.

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 sample-size illustrations translate observed contrasts into hypothetical planning requirements. They are not a report of the study's original design assumptions. The registry record does not report the original sample-size justification or the assumptions used to choose the enrollment of 144.

The planning assumptions listed are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set to the stated fraction of the observed effect. For the time endpoint, the planning table gives participants per arm: for 100% of the observed effect, 99,705 for 80% power and 133,477 for 90% power; for 75% of the observed effect, 177,253 and 237,292; and for 50% of the observed effect, 398,820 and 533,906. For the adenoma outcome, the corresponding participants per arm are 293 and 391 for 100% of the observed effect, 512 and 684 for 75%, and 1,130 and 1,511 for 50%.

“Participants per arm for 80% power” describes a hypothetical group size that, under the stated planning assumptions, would give an 80% chance of detecting the specified effect if that effect were the true one. The 90% power column uses a higher chance of detection under the same type of assumptions, and consequently calls for more participants. These are planning concepts, not guarantees about the result of a future study.

Smaller effects are harder to distinguish from random variation, so the illustrations require more participants per arm when the effect is reduced from 100% to 75% or 50% of the observed effect. The curve associated with the planning display should be read as illustrating this relationship, not as an observed trial outcome. These calculations are not observed power: they are hypothetical sample-size illustrations based on the observed effect, not a measure of the probability that this completed study detected an effect.

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 = -4.000; pooled standard deviation σ = 318.786.
2. n = 2 × (1.96 + 0.842)² × 318.786² / -4.000² = 99,704.8, rounded up to 99,705 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 <- -4                      # observed difference in means
sigma <- 318.785978361659                     # 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(6664762)
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 = 99,705 (80% power), 133,477 (90% power)
 75% of observed effect: n per arm = 177,253 (80% power), 237,292 (90% power)
 50% of observed effect: n per arm = 398,820 (80% power), 533,906 (90% power)
power.t.test: 99705.8 
Simulated power at n = 99,705 per arm: 0.798 (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 registry identifies one primary endpoint and one secondary outcome, and lists no reported analyses. It does not state whether there was a prespecified hierarchy of outcomes, a multiplicity adjustment, or a rule for interpreting secondary findings. Multiplicity matters because testing several outcomes can increase the chance that at least one result appears noteworthy even when there is no corresponding underlying effect. This is a general statistical concern, not evidence that an adjustment was or was not performed.

The secondary comparison is explicitly unadjusted. The registry does not explain whether its p-value was intended as confirmatory, whether it was part of a broader set of comparisons, or how any multiplicity was addressed. The primary p-value is also unadjusted. Without a reported analysis plan, the reader cannot determine whether the displayed tests match the planned inferential strategy or whether there were additional analyses that are not listed.

Missing-data handling is not reported in the registry record. The primary outcome population is described as 144 patients, with 72 in each group, and both secondary-outcome denominators are 72. Those denominators do not establish whether all randomized participants had complete outcome data, whether any were excluded, or how missing measurements were treated. The record does not describe participant flow, exclusions, withdrawals, or imputation.

The analysis population is also not reported. In a randomized trial, an intention-to-treat analysis generally retains participants in the groups to which they were assigned, while other analysis populations may apply different inclusion rules. This is a general distinction; the registry does not say which population was used for the posted comparisons. It also does not state whether analyses were based on assigned position or position actually received.

Additional details that would support appraisal include the prespecified statistical analysis plan, the method used for each comparison, handling of incomplete or extreme timing values, and any adjustments for baseline variables or site. These details are not reported in the registry record. Their absence limits the ability to assess whether the estimates and tests are fully reproducible and how much weight to place on secondary findings.

15. 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 0% reporting threshold.

The registry reports zero serious adverse events in each group: 0 among 72 participants assigned to left lateral positioning and 0 among 72 assigned to supine positioning. It also reports zero other adverse events in each group and zero deaths in each group. These are the counts in the adverse-event fields recorded for the two arms.

Zero reported events should be interpreted narrowly. It describes what the registry record reports, not proof that no event occurred or that the positions have no risks. The record does not provide definitions of serious or other adverse events, the method or period of event collection, or additional detail about attribution. It also does not report separate event terms; the list of serious-event terms is empty.

These figures are a safety summary, not a comparative safety analysis. With no reported events in either group, the registry does not provide an event contrast that can estimate a difference in risk. The limited safety information should therefore be read alongside the absence of detail about ascertainment and follow-up, without drawing broader conclusions about safety.

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

The posted primary data show similar group averages for time to cecal intubation, with a mean difference estimate close to zero. The interval is wide, however, and spans values in both directions. The result does not establish that the positions produce identical timing or that any possible difference is too small to matter. It shows that the posted summary comparison does not precisely determine the size or direction of the mean difference.

The secondary outcome points toward more participants with at least one adenoma detected in the supine group, but its unadjusted interval includes no difference. As a secondary finding without a reported multiplicity plan or analysis strategy, it should be regarded cautiously. It is not sufficient on its own to establish a reliable difference in detection or to explain the primary timing result.

Random allocation is intended to support a fair comparison by reducing systematic differences in group assignment. Yet interpretation still depends on how allocation was conducted, whether outcomes were measured consistently, whether participants were analyzed as assigned, and how missing data were handled. These details are not reported in the registry record. The trial description says single-blind, but does not identify the blinded parties or explain the procedure.

The reported completion status and enrollment do not answer whether the study had adequate precision for a particular clinically important effect. The original sample-size justification and target difference are not reported in the registry record. The planning illustrations use the observed effect and are not a substitute for the original design rationale or evidence of observed power.

Accordingly, the results should be understood as estimates from this randomized comparison, with substantial uncertainty in the primary contrast and limitations in the reported analysis details. They do not establish equivalence, prove that one position is better, or support medical advice. The registry's safety fields report no events, but the record does not describe enough about adverse-event collection to draw broad conclusions from those counts.

17. Why This Trial Matters Statistically

This trial raises a useful statistical question about how to interpret a small estimated difference when the underlying measurements vary substantially. The primary point estimate is close to zero, but the interval is broad. Looking only at the point estimate or p-value could obscure the fact that the data remain compatible with meaningful differences in either direction. Precision is central to the interpretation.

The trial also illustrates the distinction between failure to find evidence of a difference and evidence that two approaches are equivalent. A conventional unadjusted test with a large p-value does not establish equivalence. That conclusion would require an appropriate design and a prespecified margin for acceptable differences; neither is reported in the registry record. This distinction is important whenever a result is described as showing “no difference.”

The secondary endpoint highlights another statistical issue: different outcomes from the same procedure can have different estimates and uncertainty. A timing measure and a detection measure address distinct features of the procedure. Their results should be evaluated on their own definitions and with attention to the primary-versus-secondary distinction. In this record, the lack of a reported multiplicity plan further limits the confirmatory weight of the secondary result.

Finally, the registry illustrates why design and analysis details matter alongside numerical results. Information about blinding, missing data, analysis populations, and the original sample-size rationale would help readers judge how the estimates were produced and how broadly they can be interpreted. The available summaries are useful, but they do not answer all questions needed for a full appraisal.

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.

The registry record leaves important design and analysis details unspecified. Although the trial is described as randomized and single-blind, it does not report the randomization procedure, allocation concealment, who was blinded, or how blinding was maintained. It does not explain whether participants remained in their assigned positions throughout the procedure or whether changes in position occurred.

The primary endpoint is defined as time from insertion to cecal intubation, but the record does not describe how timing was measured, who recorded it, or whether assessors followed a standardized process. The reported timeframe is 4-10 minutes, approximately 240-600 seconds, while the group standard deviations are 332.0 and 305.0 seconds. Without individual-level data or information about distributions, it is not possible to assess the role of skewness, outliers, or unusual values in the mean-based comparison.

The analysis methods and analysis populations are not reported, and the registry lists no reported analyses. There is no account of missing outcomes, exclusions, withdrawals, adherence, or the handling of incomplete and extreme measurements. The original sample-size rationale, clinically important difference, and any interim analyses are also not reported in the registry record. These omissions restrict assessment of whether the study was designed and analyzed to answer a particular inferential question.

The record identifies the study as multicenter but does not state the number of centers or describe how site was handled in the analysis. It also gives limited participant information beyond the colorectal cancer screening condition and group sizes. The single secondary outcome has an unadjusted comparison, while a multiplicity strategy is not reported. Finally, the adverse-event fields contain zero counts but provide no detail about definitions, ascertainment, or follow-up. These limitations apply to interpretation of the registry record and do not establish that the procedures were not conducted.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Left Lateral Position Versus Supine Position in Colonoscopy — NCT06664762.
• Registry record last updated 2026-04-29; status last verified 2026-04.
• Results first posted 2026-04-29.
• 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

NCT06664762 is a completed, randomized, parallel-group, single-blind multicenter study sponsored by Hospital Civil de Guadalajara. It compares left lateral with supine positioning during colonoscopy and reports enrollment of 144 participants, with 72 in each group for the primary outcome. The primary endpoint is mean time to cecal intubation in seconds; the secondary outcome is the number of participants with at least one adenoma detected.

The posted primary estimate is a mean difference of -4.0 seconds, with an interval from -108.1 to 100.1 seconds and an unadjusted p-value of 0.94. The secondary comparison is also unadjusted and uncertain. The registry reports zero serious adverse events, zero other adverse events, and zero deaths in each group. Details of the original sample-size justification, analysis methods, missing-data handling, and analysis populations are not reported in the registry record.