Test Catheter Pilot Study in Healthy Volunteers: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Test Catheter Pilot Study in Healthy Volunteers (NCT00832078), a randomized na study. The primary outcome is Discomfort.

2. Clinical Question

The study’s stated purpose was to evaluate the safety of an intermittent catheter in comparison with an existing catheter on the market. The posted primary outcome is discomfort, measured after each catheterisation, so the results also describe participants’ reported experience with the devices. The registry lists handling, preference and haematuria as secondary outcomes, but does not post analyses for them in the analysis count.

The reported mean score was 2.25 units for SCCM and 2.52 units for SC on a Visual Analog Scale from 0 (no discomfort) to 10 (worst imaginable discomfort). The registry reports the mean difference as -0.27, with a confidence interval extending from a negative value to a positive value. That interval includes no difference in mean scores. The result therefore describes the observed scores and the imprecision around their contrast; it does not establish that one catheter produces less discomfort.

3. Trial Design

The registry describes a randomized, single-blind, crossover study. In a crossover design, participants receive more than one study intervention, allowing outcomes under different interventions to be observed within the same participant. Such designs can make within-participant comparisons informative because each participant can serve as their own reference. The validity of that comparison can depend on features such as the timing and order of treatments, and on how the analysis accounts for repeated observations.

The record describes two treatment sequences. Group A used SCCM and then SC on test day 1, followed by SC and then SCCM on test day 2. Group B used SC and then SCCM on test day 1, followed by SCCM and then SC on test day 2. These descriptions indicate that order varied across groups. The registry does not report the number assigned to each sequence, the details of how randomization was performed, or how the order and repeated observations were handled in the primary analysis.

The study is marked single-blind, but the registry record does not state who was blinded or how blinding was maintained. The record identifies the study as completed, gives its start as 2009-01 and primary completion as 2009-04, and lists enrollment as 28. The brief summary instead describes a study including 25 healthy males. The primary outcome reports 25 participants for SC and 23 for SCCM. The record does not explain the relationship among those counts, so they should be read as different registry statements rather than reconciled into a single count.

The listed phase is NA. The record does not provide further design details such as a protocol-based rationale for the enrollment target, a planned analysis model for the crossover structure, or a statistical analysis plan. Those details are not reported in the registry record.

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: 28 participants enrolled in study. 2 were excluded before randomization as they did not comply with inclusion criteria. One was excluded from study (ITT) as participants dropped out before having any data recorded.

Test Day 1- 1 Period

Test Day 1-2 Period

Reasons for not completing this period:

Test Day 2 - 1 Period

Test Day 2 - 2 Period

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: The number analized was the number of participants catherised with each catheter at least onze during the study(SC or SCCM)

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Discomfort, measured over After each catheterisation.

The primary endpoint is discomfort after each catheterisation. The registry describes it as a continuous measure summarized by a mean and standard deviation, in units on a scale. Participants rated discomfort using a Visual Analog Scale (VAS) from 0 (no discomfort) to 10 (worst imaginable discomfort). A score on this scale gives a numerical summary of a participant’s reported sensation rather than a count of events.

Using a mean provides a summary of the central level of reported discomfort within each catheter group. The standard deviation describes how spread out the individual scores are around that group mean. Neither summary alone shows the full distribution of scores or how each participant’s score changed between catheters.

Discomfort is relevant to the study’s stated comparison because it captures participants’ reported experience after using each device. The primary outcome timeframe is after each catheterisation, so the measure concerns an assessment tied to each use rather than a single assessment at the end of the study. The registry describes the analyzed population as participants catheterized with each catheter at least once. It does not report the specific handling of repeated ratings, missing ratings, or within-participant dependence in the analysis.

The record also lists handling, preference and haematuria as secondary outcomes. Their presence indicates additional areas of interest, but the registry does not post their results in the analysis count. The posted primary endpoint should therefore be interpreted on its own: it quantifies mean reported discomfort on the stated scale and does not by itself summarize every aspect of safety or user experience.

7. Results Posted in the Registry

• Test Catheter SCCM: mean 2.25 versus 2.52 on control; difference -0.27 (95% CI -1.20 to 0.66), standardized effect d = -0.16; z-test p = 0.571.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is a continuous measure, and the registry identifies its summary statistic as a mean with standard deviation. A mean represents the arithmetic center of a set of scores. A standard deviation describes the spread of those scores around the mean. Together, they give a compact account of the location and variability of discomfort ratings, but they do not reveal the complete distribution or whether scores are clustered, skewed or affected by unusual observations.

What does the mean difference represent?

The posted mean difference compares the SCCM mean with the SC mean. Its estimate is -0.27 units. The negative sign indicates that the observed mean for SCCM was lower than the observed mean for SC. The estimate is expressed in the VAS scale’s units, so it remains tied to the outcome’s interpretation. It is not a percentage or a standardized score.

A difference in sample means is an estimate of a population contrast, subject to sampling variability. The confidence interval communicates that uncertainty. If the interval includes zero, the data do not clearly distinguish the estimated contrast from no mean difference under the analysis used. An interval containing zero does not show that the means are identical; it shows that the data leave no difference among the compatible possibilities.

Why does the crossover design matter?

In a crossover study, the same participant may contribute an outcome under each intervention. The observations are therefore potentially related. A paired analysis uses the within-participant relationship, whereas an analysis that treats observations as independent does not use that relationship in the same way. The appropriate approach depends on the design and the available data. The registry record does not report which approach was used for the discomfort comparison, so the posted estimate cannot be described as a particular paired or repeated-measures analysis.

Order is also part of a crossover design. The record describes sequences that reverse the order of catheter use across test days. Randomizing sequence can help avoid systematic assignment of one order to one group, but the registry does not report the randomization procedure or sequence counts. It also does not state whether the analysis addressed possible period or carryover effects. Those possibilities matter as general design considerations; the record does not establish that any such effect occurred.

How should the p-value be read?

The unadjusted p-value is 0.571. In general, a p-value is calculated under a null hypothesis and a statistical model. It indicates how unusual results at least as extreme as the observed result would be if that model and null hypothesis were correct. It does not quantify the probability that a treatment has no effect, and it does not measure the size or importance of an effect. The term unadjusted indicates that the posted p-value is presented without an adjustment for multiple comparisons. The registry does not report whether any other adjustment or planned hierarchy was used.

In general, a p-value is sensitive to sample size and variability as well as the size of the estimated effect. It is therefore useful to interpret it alongside the mean difference and confidence interval. Here, the point estimate is small relative to the uncertainty described by the interval, which crosses zero. The p-value does not turn that uncertain estimate into evidence that the catheters are equivalent.

What do the planning estimates mean?

The registry includes planning illustrations calculated from the observed effect, under stated assumptions. These are hypothetical sample-size calculations, not outcomes from the trial’s original planning process. They express how many participants per arm would be needed for the specified target power if the stated fraction of the observed effect were the effect to detect, under the listed assumptions. The figures depend on those assumptions and on the observed estimate used as their starting point.

General statistical reasoning explains why sample size requirements rise when the target effect becomes smaller: a subtler difference is harder to distinguish from random variation, so more information is needed to reach a given power under the same assumptions. The planning values should not be interpreted as a retrospective evaluation of whether this study was adequately powered. The original design assumptions, including any original sample-size justification, are not reported in the registry record.

What remains unspecified?

The registry identifies the primary measure, summary type, timeframe and reported comparison, but does not report a detailed statistical analysis plan. It does not specify a model for the crossover structure, treatment of missing outcome observations, adjustment for sequence or period, or handling of protocol deviations. Nor does the record state whether the displayed standard deviations or comparison were adjusted for any covariates. These are not details that can be inferred reliably from the posted means and standard deviations.

The distinction between a descriptive summary and an inferential comparison is important. The means describe the observed scores in the reported analysis populations. The confidence interval and p-value make inferences under an analysis method, but the record does not explain that method in enough detail to assess all its assumptions. The posted figures can still be interpreted at face value, while recognizing that the crossover-specific analytical choices are not reported.

10. Confidence Intervals and Precision

The estimated mean difference is -0.27 units, with a confidence interval whose lower bound is -1.205 and whose upper bound is positive. Because the interval spans zero, it includes no mean difference as well as differences in either direction. The interval is the main guide to the precision of the effect estimate: it shows that the point estimate is not pinned down tightly enough to identify a clear direction or size of difference.

In general, a confidence interval represents uncertainty in an estimate under the statistical model used to calculate it. It is not a range containing a known fixed proportion of individual participants’ scores, and it is not a guarantee that the true effect lies within its limits. Its interpretation depends on the model and analysis assumptions. The registry does not describe the method used to calculate this interval or whether it accounts for the crossover pairing.

The reported group standard deviations are 1.5 for SCCM and 1.8 for SC. They describe variability in discomfort scores within the analyzed catheter groups, not uncertainty in the mean difference itself. The comparison also reports a pooled standard deviation of 1.663, but the record does not provide enough detail to determine how the crossover structure was reflected in that summary.

The unadjusted p-value of 0.571 is consistent with the interval’s inclusion of zero, but the p-value and interval answer different questions. The interval shows a range of effect estimates compatible with the analysis; the p-value summarizes compatibility with a null hypothesis under its model. Neither alone establishes equivalence or rules out an important difference. The width and position of the interval, together with the incompletely described analysis method, call for cautious interpretation.

11. Planning a Similar Trial: Sample Size

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

The planning figures are participants per arm, not total events. The assumptions listed for these illustrations 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 a stated fraction of the observed effect. These calculations use the observed effect as a planning reference; the trial’s own original design assumptions are not reported in the registry record.

For planning at 100% of the observed effect, the estimates are 596 participants per arm for 80% power and 798 participants per arm for 90% power. At 75% of the observed effect, the estimates are 1,060 participants per arm for 80% power and 1,418 participants per arm for 90% power. At 50% of the observed effect, the estimates are 2,383 participants per arm for 80% power and 3,191 participants per arm for 90% power.

In plain language, the 80% power column describes the planning target for a study with an 80% chance of detecting the specified effect under the stated assumptions, if that effect were present and the assumptions held. The 90% column uses a higher chance-of-detection target, which requires more participants under the same planning framework. Smaller target effects require more participants because they are harder to distinguish from random variation.

These values are planning illustrations based on the observed effect, not observed power for the completed study. They should not be read as the study’s enrollment target or as evidence about the analysis actually conducted.

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 = -0.270; pooled standard deviation σ = 1.663.
2. n = 2 × (1.96 + 0.842)² × 1.663² / -0.270² = 595.7, rounded up to 596 participants per arm for 80% power.

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

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- -0.27                      # observed difference in means
sigma <- 1.66328642726694                     # 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(832078)
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 = 596 (80% power), 798 (90% power)
 75% of observed effect: n per arm = 1,060 (80% power), 1,418 (90% power)
 50% of observed effect: n per arm = 2,383 (80% power), 3,191 (90% power)
power.t.test: 596.7 
Simulated power at n = 596 per arm: 0.799 (20000 replicates)

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

13. Multiplicity, Missing Data and Analysis Populations

The registry lists handling, preference and haematuria as secondary outcomes, in addition to the primary discomfort outcome. It reports four outcome measures but gives an analysis count of zero. The record therefore does not post analyses for the listed secondary outcomes. Their results, effect estimates and uncertainty are not reported in the registry record.

When a study examines several outcomes or makes multiple comparisons, the chance of obtaining an apparently notable result by chance can increase. Statistical methods can address multiplicity, for example through adjustments or a prespecified hierarchy. This is general statistical context, not a description of what this study did. The registry reports an unadjusted p-value for the primary comparison and does not report a multiplicity strategy, a hierarchy of outcomes, or whether additional analyses were planned.

The registry record also does not report how missing discomfort ratings were handled, whether all participants contributed observations under both catheters, or what analysis population was used beyond its description that participants were counted if catheterized with each catheter at least once. Enrollment is listed as 28, the brief summary says the study included 25 healthy males, and the outcome arm counts are 23 for SCCM and 25 for SC. The record does not explain the difference among these counts or identify exclusions or missing observations.

Because the study is a crossover, information about paired observations and the analysis population would help readers assess how the comparison was constructed. The registry does not state whether the analysis accounted for repeated observations, sequence, period or possible carryover. It also does not report a prespecified statistical analysis plan. These omissions limit the ability to evaluate how missing data, multiplicity and the crossover design may have influenced the reported inference.

14. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The posted safety figures report zero serious adverse events affecting participants in the test catheter group and zero in the standard catheter group. The serious-event denominator is 25 at risk in each group. The registry also reports zero other adverse events affecting participants in each group, with 25 at risk in each group for that category.

These are counts within the registry’s stated categories and at-risk denominators. They describe what was recorded in the posted safety results; they do not establish that no event of any kind occurred, or that the devices have equivalent safety. The registry lists no top serious-event terms.

Deaths are recorded as not reported, so the record does not give a death count. The safety data should also be considered alongside the registry’s different enrollment and outcome population counts: the record lists enrollment of 28, its brief summary says 25 healthy males, and the primary outcome reports different catheter counts. It does not explain how these counts relate to the safety denominators. The posted figures provide a limited safety summary, not a full account of event definitions, timing or ascertainment.

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

The posted results show mean discomfort scores of 2.25 units for SCCM and 2.52 units for SC on the stated VAS. The reported mean difference is -0.27 units, in the direction of a lower observed mean score for SCCM. The confidence interval includes zero and extends into positive values, while the unadjusted p-value is 0.571. Taken together, these results do not establish a clear difference in mean discomfort.

That finding is not the same as demonstrating that the catheters are equivalent. An equivalence conclusion requires an appropriate design and a prespecified range defining what differences would count as practically equivalent. Such a margin is not reported in the registry record. The interval also leaves uncertainty about the possible size and direction of the underlying contrast.

The primary outcome captures reported discomfort after each catheterisation, not every aspect of device performance or safety. Handling, preference and haematuria are listed as secondary outcomes, but their analyses are not posted. The safety results report no affected participants in the listed serious and other adverse event categories, but deaths are not reported and further details of event collection are absent.

The study’s crossover structure could support comparisons within participants, but the registry does not say how pairing or other design features were handled statistically. Nor does it explain the differences among its enrollment, summary and outcome counts. Those omissions limit how fully the inferential results can be assessed. The most defensible reading is therefore a description of the posted means and uncertain contrast, not a claim that either device is better, worse, or equivalent.

16. Why This Trial Matters Statistically

This study illustrates why an estimated effect, its uncertainty and the design details all matter in interpreting a clinical comparison. The mean difference gives a direction and scale for the observed contrast, while the confidence interval shows that the estimate remains uncertain. A p-value alone would not convey the range of effects compatible with the data or whether the estimate is precise.

The crossover design adds an important statistical consideration. When the same participant contributes observations under both interventions, those observations may be related. Correctly reflecting that relationship can affect estimated uncertainty. The registry describes randomized sequences but does not report whether the primary analysis used the within-participant structure. This is a practical reminder that a design label does not, by itself, reveal the model used to analyze the data.

The record also illustrates why enrollment and analysis counts need clear reconciliation. It lists enrollment of 28, describes 25 healthy males in the brief summary, and reports outcome counts of 23 and 25 for the catheter groups. Without an explanation of the populations and missing observations, readers cannot reconstruct how those counts arose.

Finally, planning illustrations based on an observed effect can show how assumptions and target effect sizes influence sample-size requirements. They are not evidence of the study’s original planning rationale or its observed power. In this record, the original design assumptions are not reported. Distinguishing such planning illustrations from trial results helps prevent hypothetical calculations from being mistaken for evidence generated by the completed study.

17. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The registry record leaves several trial-specific questions unresolved. It does not explain why enrollment is listed as 28 while the brief summary describes 25 healthy males, or why the primary outcome reports 23 participants for SCCM and 25 for SC. It also does not identify whether the analysis populations differed by catheter because of missing observations, exclusions or another reason. These counts should not be combined or treated as a single reconciled sample.

Although the study is described as randomized, single-blind and crossover, the record does not report the randomization method, sequence allocation counts, who was blinded, or how blinding was maintained. The group descriptions provide treatment order across test days, but the registry does not state how period or possible carryover effects were assessed. It does not explain whether repeated measurements within participants were modeled as paired or correlated observations.

The record does not provide the original sample-size justification, a detailed statistical analysis plan, or the methods used to calculate the confidence interval and p-value. It does not report how missing outcome data were handled or whether the analysis included all randomized participants. The stated analysis population description is limited to participants catheterized with each catheter at least once.

Secondary outcomes are listed, but their results are not posted in the analysis count. Multiplicity handling is not reported. Safety reporting is also limited: the registry gives counts for serious and other adverse events, but does not provide event definitions or detailed ascertainment, and deaths are not reported. These gaps limit assessment of completeness and the robustness of the posted estimates.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Test Catheter Pilot Study in Healthy Volunteers — NCT00832078.
• Registry record last updated 2012-09-05; status last verified 2012-08.
• Results first posted 2012-09-05.
• 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.

21. Record Summary

The registry record describes a completed randomized, single-blind crossover study of SpeediCath Compact Male and SpeediCath in healthy volunteers. Its primary outcome is discomfort after each catheterisation, rated on a Visual Analog Scale from 0 (no discomfort) to 10 (worst imaginable discomfort). The posted mean scores are 2.25 units for SCCM and 2.52 units for SC; the reported mean difference is -0.27, with an interval that includes zero, and the unadjusted p-value is 0.571.

The registry lists enrollment of 28, while the brief summary describes 25 healthy males and the primary outcome reports catheter-specific counts of 23 and 25. The record does not reconcile these figures. Handling, preference and haematuria are listed as secondary outcomes, but analyses are not posted. Serious and other adverse event counts affecting participants are zero in the reported groups; death counts are not reported. Details of the crossover analysis, missing data, multiplicity and original sample-size planning are not reported in the registry record.