Clinical Comparison of Two Daily Disposable Contact Lenses in a Population of Daily Disposable Contact Lens Wearers: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Clinical Comparison of Two Daily Disposable Contact Lenses in a Population of Daily Disposable Contact Lens Wearers (NCT01233076), a randomized na study. The primary outcome is Overall Vision Quality.

2. Clinical Question

3. Trial Design

The registry record describes a randomized, unmasked crossover study of two daily disposable contact lenses in daily disposable contact lens wearers with myopia. The study was sponsored by CIBA VISION and had an enrollment of 60. Its status is completed. The recorded start was 2010-10, and primary completion was 2010-11. The phase is listed as not applicable.

The two products were nelfilcon A and narafilcon B. Participants followed one of two sequences: nelfilcon A followed by narafilcon B, or narafilcon B followed by nelfilcon A. Each product was worn bilaterally in a daily-wear, daily-disposable manner for one week. This sequence structure is the defining feature of the crossover comparison: both lenses were evaluated within the study rather than assigning participants to only one product for the entire comparison.

Randomization determines assignment to the treatment sequence; it does not mean that participants or evaluators were masked. The registry lists masking as none. The record describes the primary endpoint as a participant-interpreted questionnaire rating after a week of wear, so the outcome is a subjective report rather than an objective visual measurement.

The primary analysis population was per protocol. The registry says exclusions could occur for reasons such as major protocol deviations identified through masked review, discontinuations, and missing responses. It does not report the original design assumptions, the detailed sequence allocation, or the statistical model used to account for the crossover structure. 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: This reporting group includes all enrolled and dispensed participants.

Period 1, One Week

Period 2, One Week

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Analysis conducted per protocol, with exclusions due to reasons such as: major protocol deviations as determined by masked review; discontinuations; and/or missing responses.

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 Overall Vision Quality, measured over 1 week of wear.

The primary endpoint was overall vision quality after 1 week of wear. Participants gave a single retrospective evaluation on a 10-point scale, with 1 representing poor vision quality and 10 representing excellent vision quality. The evaluation was binocular, meaning it concerned vision with both eyes together, and the rating was recorded through a questionnaire.

A patient- or participant-reported rating can capture an experience that may not be represented by a clinical measurement alone. In this study, the rating was intended to describe how participants interpreted their overall vision quality during a week of wearing each lens. Because it is a subjective scale, the result reflects the responses and perceptions recorded by participants rather than a direct measurement of visual performance.

The reported summaries are means and standard deviations for each lens. A mean gives the average score in the analyzed group; the standard deviation describes how spread out individual scores were around that average. These summaries do not show the distribution of every response or establish how each individual’s rating changed between lenses. The registry record does not report a threshold for a meaningful difference on the scale, nor does it report secondary outcome results.

7. Results Posted in the Registry

• Narafilcon B: mean 8.70 versus 8.20 on control; difference 0.50 (95% CI -0.08 to 1.08), standardized effect d = 0.31; z-test p = 0.090.

8. Statistical Interpretation

9. Statistical Methods Explained

What does a mean describe?

For a continuous outcome such as a questionnaire score, the mean is the arithmetic average of the recorded values. Here, the registry reports mean overall vision quality ratings of 8.2 with nelfilcon A and 8.7 with narafilcon B. The mean difference of 0.5 is the reported contrast between those averages, expressed in units of the rating scale. It is a group-level summary; it does not imply that every participant’s score differed by that amount.

The standard deviation describes the spread of individual ratings around the mean. The posted standard deviations are 1.7 for nelfilcon A and 1.5 for narafilcon B. A standard deviation is not the uncertainty of the mean itself. Precision of an estimated mean difference is instead conveyed by its confidence interval, which also reflects the amount of information in the comparison and the analysis used.

What does randomization contribute?

Random assignment to sequence is intended to reduce systematic differences between sequence groups at the point of assignment. In a crossover study, participants receive both products in an assigned order, so treatment comparisons can potentially use information from each participant under both products. This is a general property of crossover designs, not a description of a specific model used in this analysis. The registry record does not report the model or explain how the sequence and repeated measurements were handled statistically.

The trial was unmasked. In general, masking can reduce the influence of expectations on subjective outcomes and on the conduct or assessment of a study. Since the primary outcome was a participant rating, the absence of masking is relevant when considering how participants’ expectations might affect responses. The registry record does not report whether any other steps were used to address this possibility.

How should the p-value be read?

The unadjusted p-value was 0.09. In general, a p-value describes how unusual data at least as discrepant as the observed data would be under a specified null model, assuming that model and its assumptions are appropriate. It is not the probability that the null hypothesis is true, and it does not measure the size or practical importance of a difference. The registry record does not report the full model underlying the p-value. The term unadjusted indicates that the posted value is not presented as corrected for multiple comparisons.

Statistical significance is a convention for interpreting evidence, not a boundary that separates a real effect from no effect. The p-value should be read alongside the estimated difference and its confidence interval. Here, the interval includes zero, and the posted point estimate is a mean difference of 0.5. Neither the p-value nor the interval alone determines whether that difference matters to participants.

Why does the crossover structure matter?

Measurements from the same participant are generally related. In general, a crossover analysis may account for this within-participant association and for the order in which treatments are received. If an analysis treats related observations as independent when they are not, uncertainty estimates can be affected. The registry describes the treatment sequences but does not report the analysis method, sequence effects, period effects, or any assessment of carryover. Those aspects therefore cannot be evaluated from the posted record.

The record reports a per-protocol population, with exclusions possible for major protocol deviations, discontinuations, and missing responses. A per-protocol analysis describes participants who met the analysis criteria, but excluding participants can affect how representative the result is of everyone enrolled. The registry record does not report the number or reasons for exclusions individually, an intention-to-treat analysis, or a missing-data method.

Only one primary outcome measure is listed, and no secondary outcome results are posted. The registry record does not report a detailed statistical analysis plan, the rationale for the chosen sample size, or whether interim analyses were planned or conducted. Therefore, the reported comparison can be described, but several design and analysis choices that would help assess its assumptions are unavailable in the registry record.

10. Confidence Intervals and Precision

The estimated mean difference for narafilcon B compared with nelfilcon A was 0.5 units. Its confidence interval has a negative lower endpoint and a positive upper endpoint, so zero lies within the reported interval. The interval is therefore compatible with a range of possible differences in either direction, rather than pinning down a single precise value.

A confidence interval conveys uncertainty around an estimate under the assumptions of the statistical method used. In general, narrower intervals indicate greater precision, while wider intervals indicate that a broader range of values remains compatible with the data and model. An interval that includes zero does not prove there is no difference; it indicates that the data do not rule out zero at the interval’s confidence level. The registry record does not specify the confidence level in the outcome entry or report the model used to construct the interval.

The per-protocol outcome summaries list 59 participants for each lens, with standard deviations of 1.7 and 1.5. The reported enrollment was 60. The registry record does not explain the relationship between enrollment and the analyzed population, so the reason for the difference should not be inferred. It also does not report the within-participant correlation, which would help readers understand the precision of a crossover comparison.

The point estimate is only one part of the result. The interval and the unadjusted p-value of 0.09 show that the uncertainty around the estimate is important to its interpretation. The registry record does not provide a clinically meaningful threshold for the scale, so the interval cannot be translated into a conclusion about whether all values it spans would be important in practice.

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 for a continuous-outcome illustration. They are not total event counts. The illustration assumes a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It uses the observed effect as its reference and considers planning for 100%, 75%, or 50% of that observed effect. These are planning assumptions for the illustration, not the original trial’s reported design assumptions, which are not reported in the registry record.

The 80% power column gives the estimated participants per arm for a future study to have an 80% chance of detecting the specified effect under the illustration’s assumptions, if that effect is the true one and the statistical assumptions hold. The 90% power column describes the corresponding planning target for a 90% chance. These are prospective design calculations, not descriptions of the probability that the completed study found a true effect.

For planning at 100% of the observed effect, the figures are 162 participants per arm for 80% power and 217 participants per arm for 90% power. For planning at 75% of the observed effect, the figures are 287 and 385 participants per arm, respectively. For planning at 50% of the observed effect, the figures are 646 and 865 participants per arm, respectively. Smaller effects require more participants under the same assumptions because they are harder to distinguish from random variation.

This is not observed power. It is a planning illustration based on the observed effect, and it does not establish what the original study was designed to detect. The registry record does not report the trial’s own sample-size justification or original planning assumptions.

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 = 0.500; pooled standard deviation σ = 1.603.
2. n = 2 × (1.96 + 0.842)² × 1.603² / 0.500² = 161.4, rounded up to 162 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 <- 0.5                      # observed difference in means
sigma <- 1.60312195418814                     # 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(1233076)
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 = 162 (80% power), 217 (90% power)
 75% of observed effect: n per arm = 287 (80% power), 385 (90% power)
 50% of observed effect: n per arm = 646 (80% power), 865 (90% power)
power.t.test: 162.3 
Simulated power at n = 162 per arm: 0.797 (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 record lists one primary outcome measure, overall vision quality, and reports no secondary outcome results. It does not provide a detailed statistical analysis plan or say whether additional analyses were planned. The posted p-value is described as unadjusted. No multiplicity adjustment is reported in the registry record.

In general, when several outcomes, time points, subgroups, or comparisons are tested, the chance of obtaining at least one apparently unusual result can increase. Adjustment methods can address that issue, but whether adjustment is needed depends on the planned analysis and the interpretation intended. The available record does not establish the full set of analyses considered, so the multiplicity approach cannot be assessed beyond noting that the posted p-value is unadjusted.

The primary analysis population was per protocol. The description says exclusions could follow major protocol deviations as determined by masked review, discontinuations, or missing responses. Although the trial’s masking is listed as none, the record’s reference to masked review concerns the review of deviations; it does not establish that participants or other study personnel were masked to treatment.

The number of participants excluded for each reason, the handling of missing questionnaire responses, and the number included in each analysis are not reported beyond the outcome summaries listing 59 for each lens. The registry record does not report an intention-to-treat analysis or a sensitivity analysis for missing data. These omissions limit assessment of whether the per-protocol estimates could be affected by exclusions or incomplete responses.

The record also does not report the statistical model, a sample-size rationale, interim analyses, or a prespecified rule for interpreting the primary result. These details are not reported in the registry record and should not be inferred from the observed outcome summaries.

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 5% reporting threshold.

For each lens, the adverse-event summary lists 60 participants at risk for serious adverse events and zero affected. It also lists 60 at risk for other adverse events and zero affected. These figures describe the registry’s posted event summaries; they do not show whether every event type was collected in the same way or over identical observation periods.

A count of zero affected means that no participants were recorded with the corresponding event category in the posted summary. It does not establish that an event is impossible or that the products have no safety risks. The trial’s enrollment was 60, and the registry describes one week of wear for each lens, but the adverse-event entry does not specify a separate detailed follow-up window.

Death counts are not reported in the registry record. No serious adverse event terms are listed. The adverse-event summary should be interpreted alongside the study’s limited size and the information recorded in the registry, rather than as a comprehensive account of all possible safety outcomes.

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

The posted primary results show mean overall vision quality ratings of 8.2 with nelfilcon A and 8.7 with narafilcon B after 1 week of wear. The reported mean difference was 0.5 units, with a confidence interval that includes zero and an unadjusted p-value of 0.09. The group mean was numerically higher for narafilcon B, but the estimate remains uncertain.

These findings do not establish that the products are equivalent. Demonstrating equivalence or non-inferiority ordinarily requires a prespecified margin and an analysis designed for that purpose; such a margin or analysis is not reported in the registry record. Likewise, the results do not establish that one lens is meaningfully better for participants. A threshold for a meaningful change on the questionnaire scale is not reported.

The outcome reflects participants’ retrospective questionnaire ratings, not every aspect of lens performance or an objective measure of vision. The trial was unmasked, and the registry does not report how expectations were addressed. The comparison also concerns daily disposable lens wearers with myopia and a one-week wear period for each product; results should not be extended beyond that context without further evidence.

The primary results apply to the per-protocol analysis described in the record. The number and specific reasons for exclusions are not reported, and there is no posted intention-to-treat result or secondary outcome result. The adverse-event summary records zero participants affected in the listed categories, but this does not rule out uncommon events or risks not captured in the summary. The record supports a description of the measured ratings and their uncertainty, not a broad conclusion about all users or all outcomes.

16. Why This Trial Matters Statistically

This trial illustrates how a crossover design can compare two products through different treatment sequences. In general, crossover designs can make within-participant comparisons possible, but their analysis needs to account for the relation between repeated measurements and potentially for treatment order. The registry record identifies the sequence structure but does not report the model used, making the statistical handling of the crossover an important point of uncertainty for readers.

The primary measure is a subjective questionnaire rating. That makes the result directly about participants’ reported overall vision quality, while also making the unmasked design relevant to interpretation. Randomization addresses assignment to sequence, but it does not remove every possible influence on a participant-reported outcome.

The reported mean difference is modest relative to the scale, and the confidence interval includes zero. Reading the point estimate together with its uncertainty avoids treating a numerical difference as conclusive evidence. The registry does not identify a threshold for a meaningful score difference, so statistical evidence and practical importance cannot be equated from this record alone.

The per-protocol analysis and incomplete reporting of missing-data handling also matter. A clear account of exclusions and the analysis population helps readers understand which participants contributed to the result. Here, the registry provides a per-protocol description and outcome counts, but not detailed exclusion counts or an alternative population analysis. These features make the trial useful for discussing the interpretation of estimates, confidence intervals, crossover methods, and analysis populations without overstating what the posted result can establish.

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.

Several limitations are specific to the information recorded for this trial. The study was unmasked, and its primary outcome was a participant’s retrospective questionnaire rating. The record does not report procedures for reducing the influence of expectations on those ratings. The result therefore represents reported perceptions under the study conditions, not an objective assessment of vision.

The study used a crossover sequence, but the registry record does not describe the statistical model or report analyses of treatment order, period effects, or carryover. It is not possible from the posted information to assess whether those features were evaluated or how within-participant measurements were incorporated into the reported comparison.

The primary analysis was per protocol, with possible exclusions for major protocol deviations, discontinuations, and missing responses. The record does not report the numbers excluded for each reason, the missing-data method, or an intention-to-treat analysis. The primary outcome counts list 59 for each lens, while enrollment was 60; the record does not explain that difference.

The outcome covers 1 week of wear per lens, and the registry lists no secondary outcome results. A meaningful-difference threshold, the trial’s original sample-size rationale, and a detailed statistical analysis plan are not reported in the registry record. Death counts are also not reported. These gaps constrain conclusions about durability, other aspects of lens performance, and the broader safety profile.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Clinical Comparison of Two Daily Disposable Contact Lenses in a Population of Daily Disposable Contact Lens Wearers — NCT01233076.
• Registry record last updated 2012-07-10; status last verified 2012-01.
• Results first posted 2011-09-08.
• 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

NCT01233076 was a completed, randomized, unmasked crossover study sponsored by CIBA VISION. It compared nelfilcon A and narafilcon B daily disposable contact lenses among daily disposable lens wearers with myopia. Enrollment was 60, with each product worn bilaterally for one week in one of two treatment sequences.

The primary outcome was overall vision quality on a 10-point participant questionnaire. Per-protocol mean ratings were 8.2 for nelfilcon A and 8.7 for narafilcon B; the reported mean difference was 0.5, with an unadjusted p-value of 0.09 and a confidence interval spanning zero. The registry lists zero serious and zero other adverse events for each lens in its posted summaries.

The analysis model, detailed missing-data handling, original sample-size rationale, and secondary outcome results are not reported in the registry record.