Efficacy Comparison of Two Preoperative Skin Antisepsis Preparations in Colorectal Surgery: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Efficacy Comparison of Two Preoperative Skin Antisepsis Preparations in Colorectal Surgery (NCT01233050), a randomized na study. The primary outcome is The Primary Objective Measures the Proportion of Patients With Superficial Site Infection as Defined by the CDC..

2. Clinical Question

The clinical question is whether the proportion of participants with a superficial surgical site infection differs between two preoperative skin antisepsis preparations in open elective colorectal surgery. One preparation was 2% chlorhexidine gluconate / 70% isopropyl alcohol; the other was Iodine Povacrylex [0.7% available iodine] / 74% isopropyl alcohol. The registry describes the primary objective as comparing these preparations for prevention of superficial surgical site infection, with infections defined using CDC criteria.

The population was male and female patients age 18 years and older undergoing elective colorectal surgical procedures involving a laparotomy. The registry describes these patients as being at high risk of surgical site infection. The primary outcome was assessed within 35 days of randomization to treatment assignment. The central statistical question is about the relative observed proportions and the precision of the difference, not whether either preparation is generally effective in other settings.

3. Trial Design

The registry describes a randomized, double-blind, parallel-group study. It lists 802 participants as enrolled and records the study status as completed. The study began in 2010-12, with primary completion in 2015-02. The sponsor was the University of Pennsylvania. The listed phase is NA.

The two groups received different preoperative skin antisepsis preparations: 2% chlorhexidine gluconate / 70% isopropyl alcohol or Iodine Povacrylex / 74% isopropyl alcohol. Both interventions are described as drugs, and both arm descriptions identify the preparation as preoperative skin antisepsis. The registry identifies the procedures as elective colorectal surgery involving a laparotomy. It does not describe further procedural eligibility details beyond that summary.

The primary outcome was the number and percentage of participants with superficial surgical site infection as defined by the CDC, assessed within 35 days of randomization to treatment assignment. The registry summary says eligible participants were assessed at regular intervals for infection and that bacterial pathogens were characterized for participants with infection. Participants were to remain enrolled until 35 days postoperatively.

The posted primary outcome denominators are 392 for Chlorhexidine-Alcohol and 396 for Iodine Povacrylex-Alcohol. These are the denominators used for the posted primary comparison; the relationship between those denominators and the enrollment figure is not reported in the registry record. Details of the randomization sequence, allocation concealment, how masking was maintained, and the trial's original sample-size justification are not reported in the registry record. The record also does not report the planned statistical analysis methods.

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

Reasons for not completing this period:

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: Chlorhexidine-Alcohol arm - 8 participants were excluded after treatment administered due to inclusion/exclusion criteria Iodine Povacrylex-Alcohol Arm - 6 participants were excluded after treatment administered due to inclusion/exclusion criteria

6. Primary Endpoint

The registry lists the primary outcome as The Primary Objective Measures the Proportion of Patients With Superficial Site Infection as Defined by the CDC., measured over within 35 days of randomization to treatment assignment.

The primary endpoint counts participants who experienced a superficial surgical site infection within 35 days of randomization to treatment assignment. The registry defines the infection using CDC criteria and describes the measure as the number and percentage of participants affected. It is a binary outcome at the participant level: each participant either contributes to the event count or does not, according to the endpoint definition and observation period.

This endpoint addresses the stated objective of comparing the two skin antisepsis preparations for prevention of superficial surgical site infection following open elective colorectal surgery. A count alone does not describe the chance of an event unless it is interpreted alongside the number of participants assessed in that group. The comparison therefore uses each group's event count and denominator to estimate the group proportions and their difference.

Superficial infection is distinct from the separately listed secondary outcomes of deep wound infection and organ space infection. Those outcomes capture other infection categories and should not be combined with the primary endpoint when interpreting the primary comparison. The registry also lists time to develop surgical site infection and bacterial pathogens present in documented infection as secondary outcomes, but they are not substitutes for the primary count of superficial infections.

Using a defined observation window and an explicit infection definition makes the endpoint interpretable as a specific event proportion in this trial population. It does not, by itself, establish how completely infections were detected or how missing assessments were handled; those details are not reported in the registry record.

7. Results Posted in the Registry

• Iodine Povacrylex-Alcohol: 11.6% (46/396) versus 10.2% (40/392) on control; risk difference 1.4 percentage points (95% CI -2.9 to 5.8), risk ratio 1.14 (0.76–1.70); unadjusted two-proportion z-test p = 0.525.

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.

Time to Develop Surgical Site Infection

• 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 errors.
• Result:
  • Iodine Povacrylex-Alcohol: mean 8.70 versus 8.00 on control; difference 0.70 (95% CI -1.11 to 2.51), standardized effect d = 0.05; z-test p = 0.448.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Iodine Povacrylex-Alcohol and the control. The interval gives the range of effects that remain compatible with the data.

Number and Percentage of Participants With Deep Wound Infection

• 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:
  • Iodine Povacrylex-Alcohol: 7.1% (28/396) versus 5.6% (22/392) on control; risk difference 1.5 percentage points (95% CI -1.9 to 4.9), risk ratio 1.26 (0.73–2.16); unadjusted two-proportion z-test p = 0.401.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Iodine Povacrylex-Alcohol and the control. The interval gives the range of effects that remain compatible with the data.

Number and Percentage of Participants With Organ Space Infection

• 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:
  • Iodine Povacrylex-Alcohol: 4.0% (16/396) versus 5.1% (20/392) on control; risk difference -1.1 percentage points (95% CI -4.0 to 1.9), risk ratio 0.79 (0.42–1.51); unadjusted two-proportion z-test p = 0.475.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Iodine Povacrylex-Alcohol and the control. The interval gives the range of effects that remain compatible with the data.

The registry lists secondary outcomes covering time to develop surgical site infection, bacterial pathogens present in documented infection, deep wound infection, organ space infection, and length of hospital stay. Of these, posted numerical results are available for time to infection, deep wound infection, and organ space infection. The record lists no reported analyses for these secondary outcomes, and numerical results for bacterial pathogens and length of stay are not reported in the registry record.

The secondary comparisons do not point uniformly in one direction. The time-to-infection and deep-infection estimates are higher in the Iodine Povacrylex-Alcohol group, while the organ-space estimate is lower in that group. This mixed pattern does not provide a consistent secondary signal that would resolve the uncertainty in the primary superficial-infection comparison. These are distinct outcomes, so their directions should not be treated as interchangeable evidence about the primary endpoint.

The secondary outcomes add context about different aspects of infection and hospitalization, but they do not replace the primary question. A result for deep or organ space infection is not the same endpoint as CDC-defined superficial infection. Likewise, time to infection concerns timing rather than simply whether the primary event occurred in the specified window.

General statistical explanation: when many outcomes or comparisons are examined, the chance of at least one apparently notable result can increase, especially if the analyses are unadjusted and exploratory. The registry record does not report a multiplicity strategy or a prespecified hierarchy for interpreting secondary outcomes. Consequently, unadjusted secondary results carry less weight than the designated primary comparison and should be treated as supportive or descriptive rather than as independent confirmation.

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

• Time to Develop Surgical Site Infection
• Bacterial Pathogens Present in Documented Surgical Site Infection
• Number and Percentage of Participants With Deep Wound Infection
• Number and Percentage of Participants With Organ Space Infection
• Length of Hospital Stay

9. Statistical Interpretation

10. Statistical Methods Explained

How to read a binary outcome

The primary result is a binary outcome because participants are counted according to whether a defined event occurred during the specified observation period. For each group, the event count is interpreted against the group denominator to estimate an event proportion. The comparison can then be expressed on an absolute scale as a risk difference, or on a relative scale as a risk ratio or odds ratio. These measures answer related but distinct questions: the risk difference expresses the gap between proportions, while ratios compare one group's risk or odds with the other's.

In this comparison, the risk difference is posted as 0.014 for Iodine Povacrylex-Alcohol relative to Chlorhexidine-Alcohol. Its confidence interval runs from -0.029 to 0.058. A risk difference of zero is the no-difference reference on this scale. Because the interval crosses that reference, the estimated direction is uncertain. The risk ratio and odds ratio also have their own null reference values, and their posted confidence intervals include those values. A measure's scale matters: the numerical size of a risk difference is not directly interchangeable with a risk ratio or odds ratio.

What a confidence interval conveys

General statistical explanation: a confidence interval describes the uncertainty associated with an estimate under the assumptions of the method used to calculate it. It is not a range containing a fixed proportion of individual participant outcomes, and it does not assign a probability to the true effect after the data have been observed. A wider interval indicates less precision than a narrower interval on the same scale. For this trial's primary risk difference, the interval includes both negative and positive values, so the data are compatible with differences in either direction under the interval method. The registry record does not report the exact interval-construction method.

What the p-value can and cannot say

The unadjusted p-value for the primary comparison is 0.525. General statistical explanation: a p-value measures how unusual data at least as incompatible with a specified null model would be if that model and the analysis assumptions were true. It is not the probability that the null is true, nor does it measure the probability that the result arose by chance. A p-value should be interpreted alongside the estimated effect and its interval. Here, the estimate and interval show the direction and scale of the observed comparison and its uncertainty; the p-value alone cannot establish equivalence or the absence of a meaningful effect.

The term unadjusted indicates that the posted p-value is not presented as adjusted for other variables or multiple comparisons. The registry record does not report the planned model or whether the posted test matches a prespecified primary analysis. It lists no reported analyses, so details such as covariate adjustment, stratification, or sensitivity analyses are not reported in the registry record.

Why the outcome form matters

General statistical explanation: binary outcomes are commonly analyzed using methods that account for event counts and the number at risk or assessed. The precision of an estimate depends on both the observed event frequency and the amount of information in the data. When events are uncommon, even a seemingly large relative contrast can correspond to a small count difference and can be estimated imprecisely. Interpretation should therefore consider absolute and relative measures together, while respecting their separate scales.

These posted summaries do not supply participant-level data, so they do not allow independent checking of event timing, repeated observations, or participant characteristics. The registry describes regular assessments for infection, but details of ascertainment, adjudication, and handling of incomplete follow-up are not reported in the registry record. Those details can affect the interpretation of an event proportion and its uncertainty.

Unadjusted recalculation and analysis provenance

The comparison statistics are presented as unadjusted summaries based on the posted outcome counts and denominators. The registry lists no reported primary analyses, and no original analysis plan is reported in the registry record. Accordingly, the posted comparison should not be treated as an adjusted treatment-effect estimate. The registry record does not describe whether the analysis population was intention-to-treat, per-protocol, or defined in another way. It also does not report how participants with missing outcome assessments were included or excluded.

General statistical explanation: adjustment can account for measured baseline characteristics or design features, but it does not automatically remove bias and depends on the model and data. An unadjusted comparison is straightforward to describe, yet it may not answer the same question as an analysis that accounts for stratification or covariates. Since those design and analysis details are unavailable in the record, the safest interpretation is limited to the posted group counts, estimates, intervals, and unadjusted p-values.

11. Confidence Intervals and Precision

The primary risk difference is 0.014, and its 95% confidence interval extends from -0.029 to 0.058. This interval includes zero and spans values on both sides of the no-difference reference. The estimate therefore has limited precision for determining the direction of the contrast. The data are compatible with a lower observed proportion in the Iodine Povacrylex-Alcohol group as well as a higher one, under the stated interval interpretation.

The relative measures show a similar uncertainty pattern. The risk ratio is 1.138, with a 95% confidence interval from 0.763 to 1.698. The odds ratio is 1.157, with a 95% confidence interval from 0.738 to 1.812. Each interval includes its no-association reference, so neither relative measure sharply distinguishes the groups. The ratios are not interchangeable with the risk difference, and they should be interpreted on their respective scales.

General statistical explanation: interval width reflects sampling uncertainty under the method and assumptions used. It does not include every possible source of uncertainty, such as errors in outcome classification or bias from missing data. The registry record does not report the interval-construction method, missing-data handling, or analysis population, which limits assessment of those assumptions.

The event counts and denominators convey the amount of information contributing to the posted comparison. They do not, on their own, guarantee high precision. The confidence interval is the more direct guide to how closely the estimate is determined by the posted data. Its inclusion of differences in either direction means that the comparison should not be reduced to the point estimate or p-value alone.

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 illustrations are expressed as participants per arm for 80% power and participants per arm for 90% power. They are not total event counts. The assumptions listed for these illustrations are a two-sided significance level 0.05, equal allocation between the two arms, and a normal approximation. The effects considered are stated fractions of the observed effect: 100% of the observed effect, 75% of the observed effect, and 50% of the observed effect.

The 80% power column means the planned number of participants per arm under the stated assumptions for a design with an 80% chance of detecting the specified effect if that effect were the true one. The 90% power column describes the corresponding planning target with a 90% chance under those assumptions. These are design calculations, not descriptions of the participants actually enrolled in this trial.

Across the planning scenarios, smaller effects require more participants per arm to reach the same power target. That pattern follows because a smaller separation between groups is harder to distinguish from sampling variation. The figures are illustrations based on the observed effect, rather than the trial's own original design assumptions. The original sample-size justification and design assumptions are not reported in the registry record. This is not observed power.

For the primary comparison, the planning display gives participants per arm for each stated effect fraction and power target. The displayed values should be read as conditional planning quantities, not as evidence about whether the completed trial was adequately designed or whether a particular effect is important. Their interpretation depends on the listed assumptions and on treating the observed effect as the basis for the illustration.

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, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.102; treatment proportion p₁ = 0.116; average p̄ = 0.109.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.4409 = 0.8642.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.4408 = 0.3710.
4. n = (0.8642 + 0.3710)² / (0.0141)² = 7,650.9, rounded up to 7,651 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 <- 0.102040816326531                          # control proportion
p1 <- 0.116161616161616                          # 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(1233050)
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 = 7,651 (80% power), 10,242 (90% power)
 75% of observed effect: n per arm = 13,409 (80% power), 17,951 (90% power)
 50% of observed effect: n per arm = 29,734 (80% power), 39,805 (90% power)
power.prop.test: 7650.9 
Simulated power at n = 7,651 per arm: 0.804 (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.

14. Multiplicity, Missing Data and Analysis Populations

The registry identifies a primary objective and lists several secondary outcomes, but it does not report a multiplicity-adjustment plan, a hierarchy of hypotheses, or a family of confirmatory tests. The record lists no reported analyses. It therefore does not establish whether the posted comparisons were prespecified, whether all planned outcomes were reported, or how any multiplicity was handled.

General statistical explanation: multiplicity arises when several hypotheses are tested. If each test is interpreted without accounting for the number of tests, the chance of at least one false-positive finding across the set can be greater than for a single test. Adjustment methods or a prespecified testing sequence can address that issue, but the choice depends on the scientific plan. Because such a plan is not reported in the registry record, no adjustment should be assumed for the posted unadjusted p-values, particularly for secondary outcomes.

The record does not report the analysis population, such as whether participants were analyzed according to randomized assignment or according to treatment received. It also does not report exclusions after randomization, the number with complete primary outcome assessment, or how missing outcome data were handled. The stated group denominators are available for the posted primary comparison, but they do not establish the disposition of every enrolled participant.

General statistical explanation: missing outcome data can affect an estimated event proportion when the probability of missingness is related to the outcome or differs between groups. Different assumptions and methods for handling missingness can lead to different estimates. Without a reported missing-data strategy and participant flow, the degree to which incomplete follow-up could affect the comparison cannot be assessed from the registry record.

The registry describes regular infection assessments and enrollment through 35 days postoperatively, but detailed assessment schedules, adjudication procedures, and analysis rules are not reported in the registry record. These omissions do not change the arithmetic of the posted comparison, but they limit evaluation of its design, robustness, and intended inferential status.

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's serious adverse event figures list 0 serious adverse events among 392 participants at risk in the Chlorhexidine-Alcohol group and 0 among 396 participants at risk in the Iodine Povacrylex-Alcohol group. The record lists 1 death in each group. These are reported counts, not estimates of a causal effect of either preparation.

The adverse-event record does not list serious adverse event terms. It also records 0 other adverse events in each group among the stated numbers at risk. A zero count in a registry entry means that no events were recorded in that category in the posted results; it does not establish that the risk is absent or that all possible events were captured.

The registry record does not report whether the deaths were considered related to study treatment, the circumstances or causes of death, or additional safety analyses. The death counts should therefore be described separately from the serious adverse event counts and should not be attributed to a preparation based on these figures alone. Safety interpretation is limited to the recorded categories and counts.

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

The posted primary data show 40 of 392 participants with superficial surgical site infection in the Chlorhexidine-Alcohol group and 46 of 396 in the Iodine Povacrylex-Alcohol group. The estimated risk difference is 0.014, with a 95% confidence interval from -0.029 to 0.058 and an unadjusted p-value of 0.525. The point estimate is positive for the Iodine Povacrylex-Alcohol group relative to Chlorhexidine-Alcohol, but the interval includes values on both sides of zero.

This result does not establish that the preparations are equivalent. Equivalence requires a prespecified margin and an analysis designed to assess whether the difference lies within that margin. The registry record does not report such a margin or analysis. Nor does the result establish that one preparation is superior: the confidence interval includes differences in either direction, and the unadjusted p-value does not provide evidence that separates the groups at a conventional threshold.

General statistical explanation: a failure to detect a difference is not the same as evidence that no difference exists. The estimated effect and confidence interval describe what the data can support with the available precision, while the design and analysis assumptions shape how far the result can be generalized. Here, the interval is broad enough to leave uncertainty about both direction and magnitude.

The result pertains to the studied population, the two specific formulations, and the superficial infection endpoint assessed within 35 days of randomization. The registry does not support extrapolating it to other procedures, other products, or outcomes beyond the stated observation period. The secondary results concern different outcomes and do not remove the uncertainty around the primary comparison. The appropriate statistical conclusion is that the posted primary comparison is inconclusive about the direction of a difference, not that the preparations have been shown to be the same or different.

17. Why This Trial Matters Statistically

This trial illustrates why a clinical comparison should be read through both its effect estimate and its precision. The primary point estimate favors a higher observed superficial infection proportion in the Iodine Povacrylex-Alcohol group, but the confidence interval includes differences in either direction. Reporting only the point estimate would overstate what the data determine; reporting only the p-value would obscure the range of effects compatible with the estimate.

The case also distinguishes a randomized design from a fully documented statistical analysis. Randomized, double-blind, parallel-group allocation is recorded, but the registry does not report the original sample-size justification, the planned analysis, the analysis population, or missing-data procedures. Those omissions mean that the posted unadjusted comparison can be described, while its relationship to a prespecified inferential plan cannot be evaluated from the registry record.

The secondary outcomes show why endpoint definitions matter. Superficial, deep, and organ space infections are separately listed outcomes, and timing of infection is another distinct measure. Different directions across those results are not inherently contradictory; each answers a different question. They also raise the importance of a clearly specified multiplicity plan when several outcomes are considered.

Finally, the planning illustrations are not a retrospective score of the completed study. They use the observed effect as a planning basis and show that smaller target effects call for more participants under the listed assumptions. Keeping those illustrations separate from the trial's actual design and from observed results is essential for sound statistical interpretation.

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 trial-specific details needed to assess the robustness of the comparison are not reported in the registry record. The record does not describe the randomization sequence or allocation concealment, nor does it explain how double blinding was maintained for the two visibly different formulations. The registry identifies the study as double-blind but does not provide further operational details.

The original sample-size justification and planned statistical analysis are not reported. The registry lists 802 enrolled participants, while the primary outcome comparison uses denominators of 392 and 396. The participant flow connecting enrollment to those analysis denominators is not reported in the registry record. The analysis population, post-randomization exclusions, and handling of missing primary outcome data are also not reported.

Outcome ascertainment is described as regular assessment for infection, with CDC criteria for the superficial infection endpoint, but the record does not report details of assessment timing, adjudication, assessor training, or completeness of follow-up. It also does not report the method used to calculate confidence intervals or p-values. These limits prevent independent evaluation of the analysis assumptions from the registry summary alone.

The registry reports no primary or secondary analyses, and no multiplicity approach is reported. Several secondary outcomes are listed, but numerical results are not posted for all of them. Safety reporting gives counts, but the relationship of deaths to treatment and detailed circumstances are not reported. These limitations call for a restrained reading of the posted summaries rather than assumptions about unreported procedures or results.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Efficacy Comparison of Two Preoperative Skin Antisepsis Preparations in Colorectal Surgery — NCT01233050.
• Registry record last updated 2018-07-18; status last verified 2018-06.
• Results first posted 2017-09-05.
• 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

NCT01233050 is a completed randomized, double-blind, parallel-group study sponsored by the University of Pennsylvania. It compared two preoperative skin antisepsis preparations in elective colorectal surgery involving a laparotomy. The registry lists 802 enrolled participants, with primary completion in 2015-02.

The primary endpoint was the number and percentage of participants with CDC-defined superficial surgical site infection within 35 days of randomization. The posted risk difference for Iodine Povacrylex-Alcohol compared with Chlorhexidine-Alcohol was 0.014, with a 95% confidence interval from -0.029 to 0.058 and an unadjusted p-value of 0.525. The interval includes differences in either direction, leaving the primary comparison uncertain. Planned analyses, missing-data handling, and the original sample-size justification are not reported in the registry record.