Overall Performance of a 1-day Silicone Hydrogel Lens When Habitual Soft Lens Wearers Are Refit: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Overall Performance of a 1-day Silicone Hydrogel Lens When Habitual Soft Lens Wearers Are Refit (NCT02588573), a randomized na study. The primary outcome is Comfort.

2. Clinical Question

The registry record addresses subjective lens comfort after 8 hours of wear among habitual soft contact lens wearers with myopia. Its objective describes two habitual wearing groups: daily disposable hydrogel lens wearers and frequent replacement lens wearers. The study compared comfort ratings associated with etafilcon A, the control lens, and somofilcon A, the test lens.

The comparison is about a rating on a defined scale, not a direct measure of every aspect of lens performance. The registry record does not report a threshold for a meaningful difference in comfort, so the statistical estimates should be read as differences in the recorded scale values rather than as proof of a practically important distinction.

3. Trial Design

The registry lists the study as completed, with randomized allocation and double masking. It records the model as single group. At the same time, its arm descriptions state that subjects in each habitual wearing group were randomized to wear either the test or control lens in either the left or right eye. These details describe random allocation at the eye level, but the registry record does not report the full analysis approach or clarify how the single-group model designation relates to the arm descriptions.

The record lists two habitual lens-wearing groups and four outcome arms: habitual etafilcon A wearers assigned to etafilcon A or somofilcon A, and habitual frequent replacement wearers assigned to etafilcon A or somofilcon A. Each listed arm reports n=45. The registry enrollment is 103; that figure should not be treated as a sum of the arm counts, because the record describes lens assignments by eye and does not explain the relationship between enrollment and those outcome counts.

The listed interventions are etafilcon A as control and somofilcon A as test. The primary outcome is subjective comfort measured after 8 hours. The registry record gives a start of 2015-10 and primary completion of 2016-03. The original sample-size rationale, the protocol’s analysis plan, details of masking implementation, and the intended handling of the eye-level structure are not reported in the registry record.

The design details matter when interpreting the posted comparisons. If measurements from two eyes of the same participant were analyzed, their relationship could affect uncertainty estimates; however, the registry record does not provide enough information to establish whether the reported analysis accounted for paired eyes. The summary statistics therefore support a description of the posted results, but not a reconstruction of the trial’s full design or sponsor analysis.

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: Of the 103 enrolled, 13 participants were not eligible due to screen failure. This reporting group includes 90 participants (180 eyes) belonging to 2 groups of 45 habitual wearers of either etafilcon A lens or frequent replacement lenses (FREQ). All participants were randomized to wear etafilcon A in one eye and somofilcon A in the fellow eye.

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.

6. Primary Endpoint

The registry lists the primary outcome as Comfort, measured over 8 hours.

The primary endpoint is comfort, recorded as a mean on a 0-100 scale after 8 hours. The registry describes the measure as a subjective rating of lens comfort: 0 means the lens cannot be worn and causes pain, while 100 means it cannot be felt ever. Higher values therefore correspond to higher reported comfort on this scale.

A continuous rating preserves gradations in participants’ responses rather than reducing comfort to a yes-or-no outcome. Reporting a group mean gives a measure of the average recorded rating, while the standard deviation describes how spread out ratings were within that group. Neither summary alone describes every participant’s experience, and the mean should not be read as the rating of a typical individual without further information about the distribution.

Comfort is relevant to the stated objective because the study set out to compare the subjective comfort profile over 8 hours for the two lens types in habitual soft lens wearers. The registry record does not report a minimally important difference or a validated threshold for interpreting a particular change in scale units. Consequently, the outcome can be described in scale units, but the clinical or practical importance of a difference cannot be determined from the record alone.

7. Results Posted in the Registry

• Habitual Etafilcon A Wearers Randomized to Somofilcon A: mean 77.00 versus 83.00 on control; difference -6.00 (95% CI -14.12 to 2.12), standardized effect d = -0.31; z-test p = 0.148.
• Habitual FREQ Wearers Randomized to Etafilcon A: mean 83.00 versus 83.00 on control; difference 0.00 (95% CI -6.43 to 6.43), standardized effect d = 0.00; z-test p = 1.000.
• Habitual FREQ Wearers Randomized to Somofilcon A: mean 83.00 versus 83.00 on control; difference 0.00 (95% CI -6.82 to 6.82), standardized effect d = 0.00; z-test p = 1.000.

8. Statistical Interpretation

9. Statistical Methods Explained

The outcome is continuous: each comfort rating lies on a 0-100 scale, and the registry reports group means and standard deviations. A mean difference compares the average rating in one arm with the average in the reference arm. In these recalculated comparisons, negative values indicate a lower mean in the named arm than in the etafilcon A reference arm; a value of 0.0 indicates equal posted means. This direction describes the arithmetic contrast, not a judgment about clinical value.

What does a standard deviation describe?

A standard deviation describes the spread of individual ratings around a group mean. It is not the uncertainty in the mean itself and is not a range containing every participant’s rating. For example, the reported means of 83.0 occur alongside standard deviations of 17.0, 22.0, 14.0, and 16.0 in the four arms. This variation is a reminder that an average does not capture the full distribution of subjective ratings.

How should the mean differences be read?

The recalculated mean differences use posted summary statistics for the arms. For the habitual etafilcon A group, the comparison of the somofilcon A arm with the etafilcon A reference has an estimate of -6.0. In each frequent replacement comparison, the reported difference is 0.0 because the corresponding posted means are both 83.0. These are unadjusted comparisons; the registry record does not report an adjusted model or a sponsor analysis.

General statistical explanation: a difference estimate is a point estimate, or one summary of the contrast supported by the data. It is not an exact description of the underlying population difference. The confidence interval communicates uncertainty around that estimate under the assumptions used to construct it. The recalculations use the posted group summaries, and do not establish whether the original analysis accounted for the eye-level allocation described in the registry.

What does an unadjusted p value tell the reader?

The p values listed for these comparisons are unadjusted: 0.148 for the habitual etafilcon A comparison and 1.0 for each frequent replacement comparison. General statistical explanation: a p value measures how unusual data at least as incompatible with a specified null hypothesis would be under that hypothesis and the analysis assumptions. It is not the probability that the null hypothesis is true, nor does it measure the size or importance of an effect. A p value of 1.0 does not prove equal outcomes, and a value above a conventional threshold does not prove there is no difference.

Because these p values accompany recalculated summary-statistic comparisons, they should not be mistaken for sponsor-reported inferential results. The registry record lists zero analyses. It does not state a prespecified significance threshold for the trial’s own analysis or provide a statistical analysis plan. In particular, the record does not establish how comparisons across the outcome arms were to be handled.

Why might the design structure matter?

The registry says participants were randomized to wear the test or control lens in either the left or right eye. General statistical explanation: when two measurements come from the same person, they may be related. An analysis that accounts for such within-person dependence can have different uncertainty from one that treats observations as independent. The registry record does not describe the calculations or indicate whether the eye-level relationship was modeled. This missing detail limits how fully the posted unadjusted calculations can be evaluated.

The record also describes the model as single group, while listing four outcome arms and randomized lens assignments. These labels do not by themselves reveal the full analysis population, whether observations were paired, or how missing ratings were handled. Those details are not reported in the registry record.

What does the scale allow, and what does it not establish?

The 0-100 rating retains more gradation than a binary outcome, but it remains a subjective measure. The record gives the scale anchors but does not report a meaningful-difference threshold, distributional assessment, or any further validation detail. A mean difference in scale units is therefore interpretable as a contrast in average recorded ratings, while its importance to participants cannot be established from the information recorded.

General statistical explanation: with continuous outcomes, mean-based methods commonly rely on assumptions about the distribution and variability of observations. The registry record does not state which method the trial planned to use, whether assumptions were checked, or whether any transformations or adjustments were applied. These omissions do not invalidate the posted descriptive summaries, but they prevent a complete assessment of the original inferential method.

10. Confidence Intervals and Precision

Each mean difference is accompanied by a 95% confidence interval, which expresses the uncertainty of the estimate under the method used to calculate it. The interval is not a range that is guaranteed to contain the true difference, nor does it describe the spread of individual comfort ratings. Standard deviations and confidence intervals answer different questions: the former describe variation among ratings, while the latter describe uncertainty about a group contrast.

For habitual etafilcon A wearers, the recalculated mean difference for somofilcon A relative to the control is -6.0, with a 95% confidence interval from -14.12 to 2.123. This interval includes zero and extends to both negative and positive values. Thus, the estimate is not precise enough to rule out either direction of difference within the range represented by the interval.

For habitual frequent replacement wearers, the comparison with etafilcon A has a mean difference of 0.0 and a 95% confidence interval from -6.434 to 6.434. The comparison with somofilcon A also has a mean difference of 0.0, with a 95% confidence interval from -6.821 to 6.821. Both intervals include zero. Their widths show that the point estimates should not be interpreted as evidence that the underlying differences must be exactly zero.

The registry record does not report a clinically meaningful threshold for this scale, so the intervals cannot be classified against such a threshold. It also does not report whether the uncertainty calculations account for the stated eye-level randomization. The intervals are recalculated from posted summary statistics and should be interpreted with that limitation in mind.

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. They are an illustration based on the observed effect in the habitual etafilcon A comparison, not the trial’s original design calculation. The registry record does not report the original sample-size assumptions or justification.

The stated planning assumptions 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 as a stated fraction of the observed effect. The listed scenarios are planning for 100% of the observed effect, planning for 75% of the observed effect, and planning for 50% of the observed effect.

The 80% power column gives the participants per arm indicated by those assumptions for an 80% chance of detecting an effect of the specified size, if that effect were the true one and the assumptions held. The 90% power column gives the corresponding planning figure for a 90% chance. These are design calculations, not outcomes measured in this trial, and this is not observed power.

The figures rise as the target effect becomes smaller: under the stated assumptions, planning for a smaller fraction of the observed effect requires more participants per arm. These illustrations do not establish that the trial was designed with those assumptions, and they should not be read as evidence that a particular future study would achieve the stated power unless its design and analysis assumptions are suitable.

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 = -6.000; pooled standard deviation σ = 19.660.
2. n = 2 × (1.96 + 0.842)² × 19.660² / -6.000² = 168.5, rounded up to 169 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 <- -6                      # observed difference in means
sigma <- 19.6596032513375                     # 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(2588573)
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 = 169 (80% power), 226 (90% power)
 75% of observed effect: n per arm = 300 (80% power), 402 (90% power)
 50% of observed effect: n per arm = 675 (80% power), 903 (90% power)
power.t.test: 169.5 
Simulated power at n = 169 per arm: 0.795 (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 6 outcome measures, but it does not report a multiplicity adjustment plan for the comfort comparisons. It lists zero analyses, and no secondary results are posted. The available outcome information therefore does not establish which comparisons were prespecified as confirmatory, how multiple comparisons were to be handled, or whether any adjustment was applied in the trial’s own analysis.

General statistical explanation: when many outcomes or comparisons are assessed, the chance of observing an apparently notable result by chance can increase. A prespecified strategy for handling multiple testing helps readers understand how that issue was addressed. The registry record does not report such a strategy, so the recalculated p values should be read as unadjusted results rather than as multiplicity-controlled evidence.

The registry record also does not report the number of missing comfort ratings, the reasons for missingness, or the method used to handle missing data. It does not specify whether the primary analysis included all randomized participants, only participants with observed ratings, or another analysis population. The reported arm counts alone do not resolve these questions.

These omissions matter for interpretation. If available ratings differed systematically from unrecorded ratings, the observed means might not represent all randomized participants in the same way. This is a general concern, not a claim that missing data occurred or affected these results; the registry record does not report the necessary details to assess it.

Finally, the record describes randomized assignment by eye but does not report whether the primary analysis accounted for the relationship between eyes from the same participant. That feature could affect standard errors and confidence intervals. Without the analysis plan, population definitions, missing-data details, and multiplicity approach, the posted summaries do not allow a full audit of the trial’s intended analysis.

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 adverse event record reports zero serious adverse events affected and zero other adverse events affected in each of the four listed lens and habitual-wearer groups. Each group lists 45 at risk for both the serious and other adverse event summaries. The death count is not reported in the registry record.

These entries describe what was recorded in the registry, not a guarantee that no events could occur or that every possible event was captured. Zero reported affected participants in a group should be read as a registry count for the stated category and group. The record does not provide event definitions, collection procedures, follow-up details for safety, or a narrative explaining how events were assessed.

The listed counts do not support a comparison of safety between lenses beyond noting that the registry reports no affected participants in the displayed categories. They also do not establish that the lenses have equivalent safety profiles. The registry record contains no serious adverse event terms in its reported list.

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

The posted comfort results give a descriptive account of average subjective ratings after 8 hours in the listed lens assignment groups. The habitual etafilcon A group had means of 83.0 for the control lens and 77.0 for the test lens, with a recalculated mean difference of -6.0. In the frequent replacement group, both reported means were 83.0 in the respective comparisons. The corresponding recalculated confidence intervals all include zero.

These estimates do not establish that the lenses produce identical comfort ratings. Nor do they establish that a difference is present. The intervals retain uncertainty around the estimates, and the registry does not give a threshold for interpreting what size of scale change would matter to participants. The unadjusted p values are not a measure of clinical importance and do not replace consideration of the estimates and intervals.

The endpoint is subjective comfort on a 0-100 scale, not a comprehensive measure of lens performance. The registry does not report other results that would allow conclusions about outcomes beyond the stated comfort rating. Its record of zero affected participants in the serious and other adverse event categories is a report of those entries, not proof of no risk.

The trial record also leaves important analysis questions unresolved, including how the eye-level assignment was handled, what analysis population was used, and how missing observations or multiple comparisons were addressed. The recalculated comparisons use posted group summaries and are not a substitute for an analysis plan or sponsor-reported analysis. Conclusions should therefore remain limited to the recorded means, variability, and unadjusted comparisons in the registry.

Nothing in these results alone establishes a treatment recommendation or a broader conclusion about contact lenses. The registry supports a statistical description of the posted comfort ratings, while the practical meaning and generalizability of those ratings require information not reported in the registry record.

16. Why This Trial Matters Statistically

This trial is statistically interesting because the record combines randomized eye-level lens assignment with a single-group model designation and four listed outcome arms. That combination makes the unit of analysis important. If measurements from two eyes belonging to the same person are related, an analysis that ignores that relationship could misstate uncertainty. The registry record does not explain how this issue was handled.

The subjective comfort outcome also illustrates the distinction between a group average and participant-level experience. Reported means of 83.0 can coexist with nonzero standard deviations, so equal means do not imply identical ratings. The confidence intervals add another essential layer: a point estimate alone does not show how precisely the difference has been estimated.

All three recalculated intervals include zero, but that does not establish equivalence. The registry record reports no equivalence margin and no analysis intended to demonstrate equivalence. It also does not identify a threshold for a meaningful change on the comfort scale. Those absences limit interpretation even when the mean differences are straightforward to describe.

The sample-size illustrations make a separate statistical point: planning around smaller target effects requires more participants per arm under the stated assumptions. They are not evidence about the trial’s original design or the probability that the observed result was correct. The original design assumptions are not reported in the registry record.

Together, these features show why transparent reporting of estimands, analysis populations, paired-eye handling, missing data, multiplicity, and meaningful-difference thresholds matters. Without them, readers can describe the posted summaries and their recalculated uncertainty, but cannot fully reconstruct the intended analysis or assess all sources of uncertainty.

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 has several trial-specific limitations for interpreting the comfort results. Although allocation is listed as randomized and the arm descriptions place test and control lenses in either eye, the model is listed as single group. The record does not explain this combination or specify whether the comparisons account for measurements from two eyes of the same participant.

The posted comparison estimates are recalculated from summary statistics, while the registry lists zero analyses. No sponsor analysis, statistical analysis plan, or model specification is reported. As a result, the recalculations cannot be checked against a prespecified approach, including any adjustment for eye-level pairing or other factors.

The record does not report missing comfort data, reasons for missingness, or the analysis population. It also does not report a multiplicity strategy, despite listing 6 outcome measures, and no secondary results are posted. A meaningful-difference threshold for the 0-100 comfort scale is not reported, so the practical importance of differences cannot be judged from these data alone.

Safety reporting is limited to the registry counts for serious and other adverse events. Event definitions, collection methods, and the death count are not reported in the registry record. The listed zero counts therefore should not be treated as proof of an absence of risk.

The record reports enrollment of 103 while each listed outcome arm reports n=45. Because the registry describes assignment by eye and does not explain the relationship between enrollment and outcome counts, these values should not be combined or interpreted as a complete account of the analysis population.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Overall Performance of a 1-day Silicone Hydrogel Lens When Habitual Soft Lens Wearers Are Refit — NCT02588573.
• Registry record last updated 2019-02-08; status last verified 2019-02.
• Results first posted 2019-02-08.
• 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

The registry record identifies NCT02588573 as a completed randomized, double-masked study sponsored by CooperVision, Inc. It lists myopia as the condition, a single-group model, and interventions of etafilcon A control and somofilcon A test lenses. The stated objective was to compare subjective comfort over 8 hours among daily disposable hydrogel lens wearers and frequent replacement lens wearers after refitting.

The primary outcome is mean comfort on a 0-100 scale. Four listed arms report means of 83.0, 77.0, 83.0, and 83.0, with standard deviations of 17.0, 22.0, 14.0, and 16.0. Recalculated unadjusted mean differences are -6.0 for the habitual etafilcon A comparison and 0.0 for each frequent replacement comparison; all reported confidence intervals include zero.

The registry record lists 6 outcome measures, zero analyses, and no posted secondary results. It reports zero affected participants in the serious and other adverse event categories for each listed group. Important details about the original analysis plan, missing data, multiplicity, and the handling of eye-level assignment are not reported in the registry record.