Four Week Performance Comparison Between Two Commercially Available Silicone Hydrogel Lenses: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Four Week Performance Comparison Between Two Commercially Available Silicone Hydrogel Lenses (NCT01300767), a randomized na study. The primary outcome is Comfort on Insertion.

2. Clinical Question

3. Trial Design

The registry record describes a randomized study with single masking and an enrollment of 75. Its model is listed as single group, while the intervention descriptions specify that participants wore both lenses at the same time: one randomly assigned to one eye and the other worn in the fellow eye. The comparison is therefore a contralateral, within-participant comparison, not a comparison of participants assigned to separate lens-only groups. The record does not explain the relationship between the single-group model label and this two-lens arrangement.

The study concerned two commercially marketed silicone hydrogel lenses and daily wear for up to 4 weeks. The arm descriptions state that lenses were worn approximately 5 days or more per week and at least 10 hours per day. The registry lists Clear Care® contact lens solution as an intervention as well. Further details about use of the solution are not reported in the registry record.

The primary endpoint was comfort on insertion, evaluated retrospectively by participants after 4 weeks of wear. The endpoint analysis included 70 participants for each lens. The safety groups list 74 participants at risk for each lens. Those counts differ, and the record does not explain the difference between the endpoint and safety populations beyond the stated per-protocol exclusions for the primary outcome.

The record lists the study as completed, with start in 2011-02 and primary completion in 2011-04. It lists 12 outcome measures. The original sample-size justification, planned analysis details, and specific masking procedures are not reported in the registry record. The reported comparison is unadjusted, and the record does not describe any adjustment for the paired eye-level design.

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: • One participant was enrolled but not dispensed due to failing inclusion/exclusion criteria. This participant is included in the Actual Enrollment calculation, but not in the Participant Flow or Baseline Characteristics calculations.

Overall Study

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 Comfort on Insertion, measured over 4 weeks.

Comfort on insertion is a participant-reported assessment of how comfortable the lens felt when first put in. It was recorded on a 10-point scale, where 1 meant poor and 10 meant excellent. The primary measure was a single retrospective evaluation of 4 weeks of wear, rather than a separate score for every insertion. The record identifies the measure as a mean of a continuous outcome and reports its spread as a standard deviation.

This endpoint captures a specific experience of lens wear that participants can judge directly. A mean condenses the ratings across participants into a group-level summary, while the standard deviation describes how much those ratings varied. Neither summary shows the full distribution of individual responses. The score also does not, by itself, describe other dimensions of lens performance or safety.

The analysis was per protocol. The record says that participants could be excluded for reasons such as major protocol deviations determined by masked review, discontinuation, or missing responses. Thus, the primary endpoint summarizes ratings among the participants retained for that analysis, rather than necessarily all enrolled participants. The registry does not report further details about how the questionnaire was administered, how the retrospective rating was elicited, or how missing responses were handled.

7. Results Posted in the Registry

• Balafilcon A: mean 7.50 versus 8.30 on control; difference -0.80 (95% CI -1.40 to -0.20), standardized effect d = -0.44; z-test p = 0.009.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is a continuous measure: a 10-point participant rating of comfort on insertion, summarized as a mean and standard deviation for each lens. A continuous outcome can take values along a scale, and its mean provides a compact summary of the group’s ratings. The standard deviation describes how dispersed individual ratings are around that mean. These summaries answer different questions: the mean describes the group’s average rating, while the standard deviation describes variation among ratings.

What does the mean difference express?

The posted comparison defines the difference as Balafilcon A relative to Lotrafilcon B. The means were 7.5 and 8.3, respectively, and the reported difference was -0.8. A negative difference means the first named lens in this contrast had a lower observed mean than the reference lens. The direction is important: reversing the order of the contrast would reverse the sign, even though the underlying observations would be unchanged. The posted estimate is unadjusted.

The result also gives a confidence interval from -1.4 to -0.2. In general, a confidence interval expresses uncertainty around an estimated quantity and indicates a range of values compatible with the data under the method’s assumptions. It is not a range containing a specified proportion of individual participant scores. The interval’s endpoints are both below zero, so zero is outside the reported interval. The registry record does not state the confidence level or provide enough information to verify the interval’s calculation.

How should the p-value be read?

The unadjusted p-value is 0.009. In general, a p-value describes how unusual data at least as inconsistent with a specified null hypothesis would be if that hypothesis and the test assumptions were true. It is not the probability that the null hypothesis is true, and it does not measure the size or practical importance of a difference. Because the reported value is unadjusted, it should not be read as accounting for testing across multiple outcomes or comparisons.

The posted comparison gives a pooled standard deviation of 1.811 and a standardized difference of -0.442. A standardized difference expresses the estimated contrast relative to a measure of outcome spread, which can help describe its size on a scale without the original units. It does not replace the original-scale estimate: the mean difference of -0.8 remains the direct contrast in scale units. The registry record does not state that this standardized estimate was a prespecified target or a clinically meaningful threshold.

Why does the paired design matter?

Each participant wore both lenses, one in each eye. In general, paired observations can be correlated because they come from the same person. An analysis that uses the pairing can account for shared participant characteristics, while treating the observations as independent may not represent that dependence. The registry record reports the arm-level means, standard deviations, and an unadjusted mean difference, but it does not explain whether the statistical test and confidence interval account for pairing. The posted summaries are not enough to reconstruct a paired analysis, because the within-participant differences or their variability are not reported.

Random assignment of lens to eye helps determine which eye received which lens, but does not remove all other concerns about measurement or missing data. The record says masking was single, without identifying who was masked or describing how masking was implemented. It also says the primary analysis was per protocol, with possible exclusions for major deviations, discontinuation, or missing responses. The number excluded for each reason and the missing-data method are not reported in the registry record.

What does the analysis population represent?

The primary outcome analysis lists 70 participants for each lens. Since the two lenses were worn by the same participants, those group counts should not be interpreted as two independent sets of participants. They describe the number contributing to each lens’s outcome summary. The registry does not report a participant flow that reconciles the enrollment of 75 with the endpoint and safety counts, nor does it give a separate count for every exclusion reason.

Statistical significance and precision are related but distinct. A p-value summarizes evidence relative to a null hypothesis under a test, whereas a confidence interval displays uncertainty in the estimated difference. Neither addresses whether the analysis population represents everyone enrolled, whether the outcome is important to participants, or whether the assumptions match the design. Those questions require protocol and analysis details that are not reported in the registry record.

In general, multiplicity arises when several hypotheses are tested and the chance of at least one false positive can rise if tests are considered together without adjustment. The record lists 12 outcome measures, but no secondary outcome results are posted, and the adjustment strategy is not reported. The unadjusted p-value should therefore be understood as the reported single-comparison statistic, not as a multiplicity-adjusted conclusion.

10. Confidence Intervals and Precision

The estimated mean difference for Balafilcon A relative to Lotrafilcon B was -0.8 scale units. Its confidence interval extended from -1.4 to -0.2. This interval conveys uncertainty about the estimated average contrast: values within the interval are compatible with the data under the interval method’s assumptions. It does not show the range of ratings among individual participants, and it does not mean that every participant experienced a difference within those limits.

The interval lies entirely below zero, matching the direction of the posted means: 7.5 for Balafilcon A and 8.3 for Lotrafilcon B. The unadjusted p-value was 0.009. The registry record does not state the interval’s confidence level or describe the precise method used to calculate it, so those details cannot be evaluated from the record. The interval should be read as the reported estimate of precision, not as proof that the same contrast would occur in every setting.

Precision is also distinct from practical importance. The record does not report a minimum difference considered meaningful for comfort on insertion. It therefore does not establish whether the interval’s values correspond to small or important differences from a participant perspective. The standard deviations of 1.6 and 2.0 describe spread in scores, not the precision of the mean difference. Because the endpoint is retrospective and per protocol, interpretation also depends on who contributed ratings and how the paired observations were analyzed—details not fully reported in the registry record.

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 illustrations express sample size as participants per arm for 80% power and participants per arm for 90% power. They do not give total event counts; this is a continuous outcome, and the figures are participant counts per arm. The listed assumptions are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The effect to detect is set as a stated fraction of the observed effect.

For planning at 100% of the observed effect, the illustrations give 81 participants per arm for 80% power and 108 participants per arm for 90% power. At 75% of the observed effect, they give 144 participants per arm for 80% power and 192 participants per arm for 90% power. At 50% of the observed effect, they give 322 participants per arm for 80% power and 431 participants per arm for 90% power. The 80% and 90% columns describe the target chance of detecting the specified effect under the planning assumptions if that effect is present; the higher target generally requires a larger planned sample.

Smaller effects require more participants to detect under otherwise unchanged assumptions. These figures are planning illustrations based on the observed estimate, not observed power. The original trial’s sample-size justification and design assumptions are not reported in the registry record. The illustrations use an equal-allocation two-arm framework, while the study descriptions indicate that each participant wore both lenses. They therefore should not be treated as a reconstruction of the study’s original design calculations.

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 = -0.800; pooled standard deviation σ = 1.811.
2. n = 2 × (1.96 + 0.842)² × 1.811² / -0.800² = 80.5, rounded up to 81 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 <- -0.800000000000001                      # observed difference in means
sigma <- 1.81107702762748                     # 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(1300767)
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 = 81 (80% power), 108 (90% power)
 75% of observed effect: n per arm = 144 (80% power), 192 (90% power)
 50% of observed effect: n per arm = 322 (80% power), 431 (90% power)
power.t.test: 81.4 
Simulated power at n = 81 per arm: 0.802 (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 12 outcome measures, while no secondary outcome results are posted. The primary outcome analysis is reported with an unadjusted p-value of 0.009. The record does not report whether the study had a prespecified hierarchy of outcomes, a multiplicity adjustment, or a plan for interpreting multiple comparisons. Because testing multiple outcomes can increase the chance of at least one apparently unusual result, the unadjusted p-value should be interpreted as applying to the reported comparison, not as an adjustment across all measured outcomes.

The primary endpoint population is described as per protocol. Exclusions could occur for major protocol deviations determined by masked review, discontinuations, and missing responses. The number excluded for each reason, the timing of exclusions, and the method for handling missing outcome values are not reported in the registry record. The posted endpoint counts are 70 for each lens, whereas enrollment was 75 and safety groups list 74 at risk for each lens. The record does not reconcile these counts.

Per-protocol analyses can describe outcomes among participants who meet the analysis requirements, but their interpretation depends on which participants remain and why others are excluded. Without details of the exclusions and missingness, it is not possible to assess whether the retained ratings differ systematically from those not analyzed. The record does not report an intention-to-treat analysis or sensitivity analyses for missing data.

The paired eye-level design also raises an analysis question: observations from the two eyes of one participant may be related. The registry record does not state whether the reported comparison accounted for that pairing. The masking designation is single, but the identity of the masked parties and the implementation are not reported. These omissions limit assessment of the analysis and its assumptions; they do not change the posted figures.

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.

The safety record lists 74 participants at risk in each lens group. For both Lotrafilcon B and Balafilcon A, the number affected by a serious adverse event is 0. The number affected by other adverse events is also 0 in each group. These are the counts recorded for the listed safety categories and populations.

Zero affected participants in the posted record means that no cases are counted in those categories in the registry results. It does not establish that the lenses have no risks, and it does not describe events that may not have been captured or reported. The registry record does not give further detail about how adverse events were collected, assessed, or followed over time. Death counts are not reported in the registry record.

The safety groups contain 74 participants per lens, while the primary endpoint analysis includes 70 per lens. The record does not explain the difference between these populations. Safety counts and comfort ratings answer different questions and should not be combined into a single judgment about performance.

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

The posted primary result describes average participant-rated comfort on insertion after 4 weeks of wear. The Lotrafilcon B mean was 8.3, and the Balafilcon A mean was 7.5. The mean difference for Balafilcon A relative to Lotrafilcon B was -0.8, with a confidence interval from -1.4 to -0.2 and an unadjusted p-value of 0.009. In this per-protocol analysis, the Balafilcon A mean rating was lower.

That finding is limited to the measure, time frame, participants, and analysis reported. It does not describe all aspects of lens performance, how each participant rated the lenses, or outcomes beyond the specified comfort question. The record does not report a threshold for deciding whether a difference of this size is meaningful to participants. A statistically distinguishable mean difference is not automatically a practically important one.

The trial used a contralateral arrangement: each participant wore both lenses, one in each eye, with the lens assigned to each eye at random. The record does not say whether the reported test and interval accounted for the dependence between a participant’s two ratings. The primary analysis excluded participants for reasons that could include deviations, discontinuation, or missing responses, and the record does not detail the exclusions or missing-data handling.

The safety record reports zero participants affected by serious adverse events and zero affected by other adverse events in each group of 74 at risk. Those counts are limited to what is recorded and do not establish an absence of risk. The results do not address longer wear than the stated period or other wear schedules. They describe the registry’s reported evidence and do not constitute advice about lens selection.

16. Why This Trial Matters Statistically

This study illustrates why design structure matters when interpreting a comparison. Although the registry model is labeled single group, its intervention descriptions state that each participant wore both lenses, one in each eye. This arrangement can make within-person comparison useful because both lens experiences come from the same participant. It also means that the two lens observations are related, which is relevant to estimating uncertainty. The registry does not say whether the reported analysis accounts for that relationship.

It also shows the difference between an outcome summary and the full participant experience. Mean ratings of 8.3 and 7.5 give a concise contrast on the 10-point scale, while standard deviations of 1.6 and 2.0 describe variation. Neither provides the full distribution of responses or identifies whether a group average reflects a similar change for every participant. The confidence interval adds information about uncertainty in the mean difference, but it does not establish a threshold for practical importance.

The analysis population is another important part of the result. The primary outcome was analyzed per protocol, with possible exclusions for deviations, discontinuations, or missing responses. That makes the endpoint counts and exclusions relevant to understanding what population the estimate represents. The record does not reconcile enrollment, endpoint counts, and safety counts.

Finally, the comparison is reported with an unadjusted p-value, while the record lists multiple outcomes and does not describe a multiplicity plan. This highlights why statistical evidence should be read together with the reported analysis strategy, missing-data information, and study structure. Several of those details are not reported in the registry record.

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 gives limited detail about the analysis underlying the primary comparison. It reports arm-level means, standard deviations, a mean difference, a confidence interval, and an unadjusted p-value, but does not state whether the calculation accounted for the within-participant pairing created by wearing both lenses. The model is labeled single group even though the descriptions specify randomized lens assignment to opposite eyes; the record does not explain this labeling.

The primary analysis is per protocol, and the record describes possible exclusions for major deviations, discontinuations, or missing responses. Counts by exclusion reason and a missing-data method are not reported. The endpoint analysis includes 70 participants for each lens, compared with enrollment of 75 and safety groups of 74 at risk per lens. The registry does not explain these differences.

Masking is listed as single, but the record does not say who was masked or how masking was maintained. It does not report the original sample-size justification, detailed statistical plan, or an adjustment strategy for multiple outcomes. The endpoint is a single retrospective rating after 4 weeks, and the record does not provide response distributions or a threshold for meaningful difference. No secondary outcome results are posted. These limitations constrain assessment of the estimate and its general interpretation without changing the values reported.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Four Week Performance Comparison Between Two Commercially Available Silicone Hydrogel Lenses — NCT01300767.
• Registry record last updated 2012-07-10; status last verified 2012-04.
• Results first posted 2012-05-09.
• 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

NCT01300767 is a completed randomized, single-masked study of two commercially marketed silicone hydrogel lenses in participants with myopia. The registry lists an enrollment of 75 and a daily-wear period of up to 4 weeks. Participants wore one lens in each eye, with lens assignment to eye randomized.

The primary outcome was retrospective comfort on insertion, rated on a 10-point scale after 4 weeks. The per-protocol analysis reported means of 8.3 for Lotrafilcon B and 7.5 for Balafilcon A. The mean difference for Balafilcon A relative to Lotrafilcon B was -0.8, with a confidence interval from -1.4 to -0.2 and an unadjusted p-value of 0.009. Safety groups recorded zero participants affected by serious adverse events and zero affected by other adverse events among 74 at risk per lens.

The record lists 12 outcome measures, with no secondary outcome results posted. Details about the original sample-size justification, paired-analysis method, missing-data handling, and multiplicity plan are not reported in the registry record.