Prospective Trial Comparing Two Different Polypropylene Meshes for Inguinal Hernias: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Prospective Trial Comparing Two Different Polypropylene Meshes for Inguinal Hernias (NCT01825187), a randomized na study. The primary outcome is Inguinal Hernia Mesh Insertion Times.

2. Clinical Question

The study description names other intended areas of assessment, including hospital stay, perioperative complications, recurrence, pain, comfort and postoperative quality of life. The posted result details in the registry record are limited, however. A NASA TLX survey index score is listed as a secondary outcome, but its numerical results are not included in the record.

3. Trial Design

This was a randomized, parallel-group trial with no masking reported. The registry record lists the study as completed and gives an enrollment of 75. It records a start of 2014-06 and a primary completion date of 2020-08-31. The trial has no applicable phase designation. The sponsor was South East Area Health Education Center, Wilmington, NC.

Participants in Treatment Group 1 were randomized to ULTRAPRO mesh, and participants in Treatment Group 2 were randomized to 3DMAX mesh. A separate evaluation concerned surgical residents’ ease of use and the time needed to perform surgery with the meshes. The registry’s posted outcome summaries include 24 participants in each mesh group. The record does not explain how these result counts relate to the overall enrollment of 75 or identify the analysis population.

The trial’s stated clinical aim was to compare the meshes using measures including hospital stay, perioperative complications, recurrence, pain, comfort and postoperative quality of life. It also aimed to assess mesh usability and operative time for residents. The primary outcome was mesh insertion time. The registry describes a 2 × 2 ANOVA on ranked times for the primary comparison, and separately posts a one-sided t-test analysis. The record does not explain the relationship between these approaches.

The procedural description distinguishes laparoscopic and robotic repairs when defining timing. For laparoscopic procedures, timing ran from insertion of the mesh into the trocar until completion of mesh fixation. For robotic repairs, it included mesh placement and the time required to place three suture fixation points. The registry record does not provide further details about the trial protocol, allocation procedures, or the original design assumptions.

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.

Population: No Baseline Measure data was collected from any Surgical Residents

6. Primary Endpoint

The registry lists the primary outcome as Inguinal Hernia Mesh Insertion Times, measured over During the procedure an average of an hour.

The primary endpoint was the time required for mesh insertion and fixation, measured in minutes. For laparoscopic repair, the recorded interval began when the mesh entered the trocar and ended when fixation was complete. The description specifies that laparoscopic fixation used four tacks: two in the pubic bone, one medially and one laterally on the upper portion of the mesh. The listed tack types were AbsorbaTack™, sutures, CapSure™ and OptiFix™.

For robotic repairs, timing included mesh placement and placement of three suture fixation points: at the pubis, the anterior location and the lateral abdominal wall at the top of the mesh. The registry describes the timeframe as during the procedure, with an average of an hour; that wording does not give a separate, exact endpoint window for each participant.

Procedure time is a continuous measure, and the posted summaries report its mean and standard deviation in each mesh group. Comparing this measure addresses the study’s stated question about mesh insertion time and the ease and duration of the procedure. It does not, by itself, describe patient recovery, recurrence, pain or quality of life. Those outcomes appear in the study aims, but detailed numerical results for them are not reported in the registry record.

7. Results Posted in the Registry

• 3DMAX Mesh: mean 8.70 versus 9.76 on control; difference -1.06 (95% CI -4.79 to 2.67), standardized effect d = -0.16; z-test p = 0.577.

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes the primary comparison as a 2 × 2 ANOVA applied to ranked mesh insertion times. It also posts a one-sided t-test analysis. The record does not explain whether these analyses addressed the same model, how rankings were handled in the reported analysis, or why the one-sided test was selected. The methods below explain the general statistical ideas; they do not fill in those unreported details.

What does a comparison of means estimate?

A mean is the arithmetic average of the observations in a group. For a continuous outcome such as time in minutes, comparing group means describes the difference in average recorded time between the randomized groups. The recalculated comparison is defined as the 3DMAX mean minus the ULTRAPRO mean. With that direction, a negative estimate indicates a lower observed mean in the 3DMAX group.

A mean difference is an estimate based on the participants whose results are included in the posted summaries. It is not a guarantee that every participant’s time followed the group average. The standard deviations—7.24 minutes for ULTRAPRO and 5.86 minutes for 3DMAX—describe variability around each group’s mean. They are not standard errors or confidence limits.

Why might an analysis use ranks?

In general, ranking replaces each observed value with its position relative to the other observations. A statistical analysis of ranks can be useful when the analyst wants a method that is less dependent on modeling the original measurements directly. However, the registry record does not describe the observed distribution of insertion times, report ranked results, or state why ranks were used. It therefore does not support a conclusion about the specific motivation for the described approach.

An ANOVA is a framework for comparing variation associated with groups or factors. The registry names a 2 × 2 ANOVA on ranked times but does not identify the factors represented by the two dimensions, give the model terms, or report an ANOVA result. It is not possible to infer those details from the method label alone. The outcome summaries and the posted one-sided t-test should therefore be read as separate pieces of reported information rather than silently combined into a single model description.

What does the posted t-test indicate?

In general, a t-test evaluates how compatible a difference in group means is with a specified null hypothesis, under assumptions associated with the test. A one-sided test evaluates a direction specified in advance, rather than treating departures in either direction symmetrically. The registry reports p = 0.523 for its one-sided t-test, but does not report the direction specified for that test, its test statistic, or an interval for its estimate. The record also does not say whether assumptions were assessed.

The recalculated unadjusted comparison uses posted group means, standard deviations and sample sizes to estimate a mean difference and interval. It is a simple summary-based re-calculation, not a recovery of the original trial analysis. Its p-value is 0.577. The registry record does not explain the difference between this calculation and the posted one-sided t-test, and the two values should be interpreted in the context of their stated methods.

What does a p-value describe?

In general, a p-value measures how unusual results at least as discrepant as the observed data would be under a specified null model and its assumptions. It is not the probability that the null hypothesis is true, nor does it quantify the size or practical importance of an effect. A p-value alone does not show the range of effects compatible with the data; an estimate and interval are more informative about that range.

Because the sponsor’s posted p-value comes from a one-sided t-test and the recalculated p-value is an unadjusted summary-based result, they reflect different descriptions of the analysis. The registry does not report enough methodological detail to reconcile them. The main interpretation should therefore emphasize the observed means and the recalculated interval while accurately distinguishing the sponsor’s reported test result.

What is not documented about the analysis?

The registry record does not report a full statistical analysis plan, details of the original sample-size justification, interim analyses, a missing-data strategy, or the population used for each analysis. It also does not report how multiple outcomes or tests were handled. These omissions matter because analysis choices can affect estimates and uncertainty, particularly when several outcomes or analytical approaches are considered. They do not prove that such procedures were absent; they mean their details are not reported in the registry record.

10. Confidence Intervals and Precision

The recalculated mean difference is -1.06 minutes, defined as the 3DMAX mean minus the ULTRAPRO mean. Its interval extends from -4.786 to 2.666 minutes. In general, a confidence interval describes a range of estimates compatible with the data and the procedure used to calculate it. The confidence level for this recalculated interval is not stated in the registry record, so it is not specified.

The interval includes zero and extends to values in both directions. In plain terms, the posted summary statistics do not pin down the direction or size of the mean difference with high precision: values consistent with the calculation include a lower mean time in either group and no mean difference. The interval is also wide relative to the point estimate, so the point estimate alone should not be read as a precise measure of the difference.

The group means were 9.76 minutes for ULTRAPRO and 8.7 minutes for 3DMAX. Their standard deviations were 7.24 and 5.86 minutes, respectively. Standard deviations describe variation among observed times, whereas the interval around the mean difference describes uncertainty in the estimated contrast. These are related but distinct quantities.

The interval is a recalculation from posted summary statistics, not an interval reported for the sponsor’s one-sided t-test. That test has a posted p-value of 0.523, but no associated estimate or interval in the registry record. The recalculated interval should therefore be read as a complementary summary of the available group data, not as a replacement for an unreported sponsor interval.

11. Planning a Similar Trial: Sample Size

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

The sample-size figures are planning illustrations based on fractions of the observed effect, not the trial’s original enrollment plan. For this continuous outcome, the listed values are participants per arm, not total event counts. The illustration assumes two-sided significance level 0.05, equal allocation between the two arms and a normal approximation. The original trial’s own design assumptions and sample-size justification are not reported in the registry record.

The column for 80% power gives the participants per arm that the planning calculation estimates would be needed to have an 80% chance of detecting the specified effect under its assumptions, if that effect were truly present. The 90% power column describes the corresponding planning target for a 90% chance. These are design targets, not guarantees about the result of a future study.

The listed scenarios are planning for 100% of the observed effect, 75% of the observed effect and 50% of the observed effect. The figures are 607 and 812 participants per arm for the 100% scenario; 1,078 and 1,443 participants per arm for the 75% scenario; and 2,425 and 3,246 participants per arm for the 50% scenario, for 80% and 90% power respectively. Smaller effects need more participants to detect under otherwise unchanged assumptions, which is why the planning counts rise as the target effect becomes smaller.

These figures are not observed power. They are forward-looking illustrations calculated from an effect observed in the trial, and the observed effect itself is uncertain. They should not be read as evidence that the trial was designed with these assumptions or that its findings establish a particular probability of detecting an effect.

12. How the Sample Size Is Derived

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

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -1.060; pooled standard deviation σ = 6.586.
2. n = 2 × (1.96 + 0.842)² × 6.586² / -1.060² = 606.0, rounded up to 607 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 <- -1.06                      # observed difference in means
sigma <- 6.58624323875151                     # 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(1825187)
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 = 607 (80% power), 812 (90% power)
 75% of observed effect: n per arm = 1,078 (80% power), 1,443 (90% power)
 50% of observed effect: n per arm = 2,425 (80% power), 3,246 (90% power)
power.t.test: 607 
Simulated power at n = 607 per arm: 0.801 (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.

13. Analyses Reported by the Sponsor

The registry reports the sponsor’s analysis as a one-sided t-test comparing the two mesh groups, with p = 0.523. It does not provide the sponsor analysis’s estimated difference, confidence interval or test statistic. The registry also describes the primary outcome as tested using a 2 × 2 ANOVA on ranked times, but does not give results for that analysis or explain its relationship to the posted t-test.

The recalculated summary-based comparison gives a mean difference of -1.06 minutes for 3DMAX minus ULTRAPRO, an interval from -4.786 to 2.666 minutes and an unadjusted p-value of 0.577. This recalculation uses the posted means, standard deviations and group sizes; it is not the same as reproducing the sponsor’s analysis. The registry record does not explain why the methods and p-values differ.

The sponsor’s result should be identified as the reported trial analysis, while the recalculation offers an additional, unadjusted way to summarize the posted group data. Neither p-value describes the size of an effect on its own. The sponsor’s p-value has no accompanying estimate or interval in the registry record, and the recalculated interval is not an interval from the sponsor’s test. The two results are best read with these distinctions explicit.

14. Multiplicity, Missing Data and Analysis Populations

The study description names several outcomes and objectives: hospital stay, perioperative complications, recurrence, pain score, comfort, postoperative quality of life, ease of mesh use and operative time. The primary outcome is mesh insertion time, and a NASA TLX survey index score is listed as a secondary outcome. The registry record does not describe a multiplicity adjustment, a hierarchy among secondary outcomes, or a strategy for controlling the chance of false-positive findings across multiple comparisons.

In general, evaluating multiple outcomes or conducting multiple tests can increase the chance that at least one result appears notable by chance. A prespecified testing hierarchy or adjustment can help address that issue, but the registry record does not report whether any such approach was planned or used. This absence of reporting does not establish that multiplicity was ignored; it means the record does not provide enough information to assess the approach.

The record does not report a missing-data plan, the number of participants with missing primary-outcome observations, or how missing observations were handled. It lists enrollment of 75 and primary-outcome group summaries for 24 participants in each mesh group, but does not explain the relationship between those counts. It would be inappropriate to infer why the counts differ or to treat the difference as a confirmed number of missing observations.

The analysis population is also not reported. The record does not say whether analyses followed randomized assignment, included only participants who underwent surgery, or used another population definition. It does not report protocol deviations or the handling of participants who may have had incomplete or unusable timing data. These details are important for understanding whether the analysis preserves the randomized comparison and how broadly results apply to the enrolled group.

Random allocation and parallel groups are stated, but allocation concealment, the method used to generate the sequence and the timing of assignment are not reported in the registry record. Masking is listed as none. Together, the missing analysis and allocation details limit assessment of bias and the completeness of the reported comparison.

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 adverse-event figures list 24 participants at risk in each mesh group. For ULTRAPRO, the registry records zero participants affected by serious adverse events, zero affected by other adverse events and zero deaths. The corresponding figures for 3DMAX are also zero, zero and zero among 24 participants at risk. The resident-evaluation group has no participants listed at risk.

These counts mean that the registry record does not show a serious adverse event, other adverse event or death among the participants counted at risk in either mesh group. They do not establish that such events are impossible, that no event occurred outside the recorded categories or observation period, or that the groups have identical safety profiles. The record does not give additional detail about event definitions, follow-up duration for safety, collection procedures or the reasons for the adverse-event reporting population.

The resident-evaluation group is an assessment activity rather than a patient mesh arm in these figures, and its at-risk count is zero. The registry record does not provide further safety information for that evaluation. These adverse-event counts should be interpreted as the events recorded in the registry, not as a comprehensive account of every possible harm.

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

The primary endpoint results describe the time associated with inserting and fixing the mesh. The posted mean was 9.76 minutes for ULTRAPRO and 8.7 minutes for 3DMAX. The recalculated mean difference is -1.06 minutes for 3DMAX relative to ULTRAPRO, with an interval from -4.786 to 2.666 minutes. This supports a cautious description: the observed mean was lower in the 3DMAX group, while the range of estimates compatible with the recalculation includes no difference and differences in either direction.

The result does not establish that one mesh shortens insertion time, nor does it show that the meshes are equivalent. A finding of no statistically clear difference is not the same as evidence of equivalence; equivalence requires a prespecified margin and a design and analysis suited to that question. Such a margin is not reported in the registry record.

These data also do not determine whether the meshes differ in recurrence, pain, complications, comfort, quality of life, hospital stay or resident experience. Those topics appear in the study aims, but numerical results for them are not reported in the registry record. The NASA TLX survey index score is named as a secondary outcome without a posted numerical result.

The findings apply to the recorded insertion-time summaries and should be interpreted with the available information about the analyzed groups. The enrollment is 75, while the primary-outcome summaries list 24 participants in each mesh group. The registry does not explain this relationship or identify the analysis population. Consequently, the record does not support assumptions about why some enrolled participants are not represented in the summaries.

The sponsor’s reported one-sided t-test has p = 0.523, while the summary-based recalculation has an unadjusted p-value of 0.577. The registry does not explain the methodological difference. Neither value measures clinical importance, and the sponsor’s test is not accompanied by an estimate or interval. The most informative reading combines the observed group means with the recalculated interval and keeps the limitations of the registry reporting in view.

17. Why This Trial Matters Statistically

This trial illustrates why an average difference and its uncertainty should be considered together. The group means alone suggest a lower recorded average insertion time in the 3DMAX group. The interval around the recalculated difference, however, spans zero and extends in both directions. That uncertainty changes the interpretation: the point estimate is not a precise statement of the true group difference.

The record also highlights the importance of clarity between a study’s stated statistical approach and its posted analysis. The primary outcome description names an ANOVA on ranked times, while the reported analysis is a one-sided t-test. Without further information about the model, test direction or rationale, readers cannot fully reconstruct the analysis. Reporting an estimate and interval alongside the test result would make the magnitude and precision easier to assess.

Clinical studies may set out to evaluate a broad set of outcomes, yet a registry can contain detailed numerical results for only a subset. Here, the aims include several patient and procedural outcomes, but the posted numerical comparison focuses on insertion time. Distinguishing an unreported result from a result showing no difference is essential: the registry does not report numerical findings for several outcomes named in the study description.

Finally, the enrollment and outcome-summary counts are not aligned in the record, and the analysis population is unspecified. Transparent participant accounting, missing-data reporting and analysis-population definitions would help readers understand which observations underpin the estimates. These are general reporting considerations; the registry record does not establish how the trial handled these issues outside the information it reports.

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 details about the primary analysis unclear. It describes a 2 × 2 ANOVA on ranked times but posts a one-sided t-test result, without explaining how the analyses relate, which factors entered the ANOVA, or what direction the one-sided test addressed. A full analysis plan and the rationale for these choices are not reported.

The enrollment is listed as 75, while the primary-outcome arm summaries include 24 participants per group. The record does not explain the difference in counts, identify the participants included in the analysis, or report whether the group summaries represent all randomized participants. Missing outcomes, exclusions and protocol deviations are not described, so the impact of these issues cannot be assessed.

The registry includes a broad set of intended outcomes, but detailed numerical results are not reported for hospital stay, complications, recurrence, pain, comfort, quality of life or the NASA TLX survey index score. The absence of these results limits assessment of the broader study aims. Multiplicity handling is also not reported.

The study is listed as unmasked. The registry does not describe whether outcome timing was recorded or assessed by personnel unaware of mesh assignment. It also does not report allocation concealment or the sequence-generation method. The timing description includes both laparoscopic and robotic procedures, but the record does not clarify the mix of procedures represented in the outcome summaries or how any procedural differences were handled analytically.

Finally, the record does not report a prespecified threshold for a clinically important difference in insertion time, the original sample-size justification, or detailed follow-up for the posted safety counts. These omissions constrain interpretation of clinical importance, study planning and the completeness of safety reporting.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Prospective Trial Comparing Two Different Polypropylene Meshes for Inguinal Hernias — NCT01825187.
• Registry record last updated 2022-06-14; status last verified 2022-06.
• Results first posted 2022-06-14.
• 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

NCT01825187 is a completed randomized, parallel-group trial comparing ULTRAPRO mesh with 3DMAX mesh for inguinal hernia repair. The registry lists enrollment of 75, no masking, and mesh insertion time in minutes as the primary outcome. The study description also includes resident evaluation and several clinical outcomes.

Posted primary-outcome summaries include 24 participants per mesh group. Mean insertion time was 9.76 minutes for ULTRAPRO and 8.7 minutes for 3DMAX. The recalculated mean difference for 3DMAX minus ULTRAPRO is -1.06 minutes, with an interval from -4.786 to 2.666 minutes. The registry reports a one-sided t-test p-value of 0.523 and does not provide numerical results for several other stated outcomes.

The record does not explain the relation between enrollment and analysis counts, the difference between the described and posted methods, or the analysis population. Serious adverse events, other adverse events and deaths are recorded as zero in each mesh group among 24 participants at risk.