A Clinical Comparison of Two Daily Disposable Soft Contact Lenses: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Clinical Comparison of Two Daily Disposable Soft Contact Lenses (NCT04005885), a randomized na study. The primary outcome is Subjective Scores of Comfort on Insertion.

2. Clinical Question

This is a comparison of reported comfort under the study’s lens-wearing conditions, not a general evaluation of every aspect of lens performance. The primary outcome focuses on the experience of putting in the lens; separate listed outcomes address overall comfort, comfort before removal, and lens centration. The registry record does not report a prespecified threshold for a meaningful difference in comfort scores. Therefore, the numerical contrast can be described, but the record does not establish how large a difference participants would consider important.

3. Trial Design

The study is registered as completed, with 55 participants enrolled. It is described as randomized, double-masked, bilateral, and crossover, with a direct refit from existing comfilcon A monthly-lens wear. The registry lists the start date as 2019-03-01 and the primary completion date as 2019-11-08. Phase is listed as NA.

Participants first wore comfilcon A on a daily-wear, reusable basis for 1 month. They were then randomized to one of two sequences: somofilcon A followed by stenfilcon A, or stenfilcon A followed by somofilcon A. Each daily disposable test lens was worn for 1 week. Because each participant was assigned a sequence of both test lenses, the crossover structure is central to understanding the design: measurements under the two lenses arise from different periods of the same study and the order was randomized.

The primary outcome summaries list 51 participants for somofilcon A and 52 for stenfilcon A. Those arm-level counts need not equal the enrollment count, and the registry record does not explain the difference or give a participant-flow account. It also does not report whether or how an analysis accounted for repeated measurements within participants, period effects, or sequence effects. The posted comparison should therefore be read in light of the crossover design without assuming a particular model for it.

The record identifies CooperVision, Inc. as the sponsor and names comfilcon A, somofilcon A, and stenfilcon A as device interventions. Detailed protocol procedures beyond the recorded wear sequence, masking, and design description 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: All subjects were fitted with comfilcon A for one month and then the subjects were randomized to wear two daily disposable lenses for one week.

First Intervention

Reasons for not completing this period:

Second Intervention

Reasons for not completing this period:

Third Intervention

Analysis population for the primary outcome, as defined in the registry: One subject discontinued after dispensing visit.

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 Subjective Scores of Comfort on Insertion, measured over 1 week.

The primary endpoint is the mean subjective comfort score on insertion after 1 week. Participants rated comfort on a scale from 0 to 100: 0 is described as causing pain and being intolerable, while 100 is described as excellent and not felt. The endpoint therefore captures the participant’s reported experience when inserting the lens, rather than an objective measure of lens fit or a clinical examination finding.

A mean summarizes the average score in each lens group. The standard deviation describes how spread out individual scores are around that group mean; it is not the uncertainty in the mean itself. Considering both values helps distinguish the average rating from the variability of participants’ experiences.

Comfort on insertion is one dimension of lens experience. It is accompanied in the registry by other subjective comfort measures and lens-centration outcomes, which can describe related but distinct aspects of wearing the lenses. The primary endpoint’s use does not mean it captures every possible benefit, drawback, or safety outcome. The registry record does not report a threshold defining a clinically important score difference or explain why this particular comfort measure was selected as primary.

7. Results Posted in the Registry

• Stenfilcon A Contact Lens: mean 90.40 versus 90.30 on control; difference 0.10 (95% CI -4.81 to 5.01), standardized effect d = 0.01; z-test p = 0.968.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Subjective Scores on Overall Comfort

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Stenfilcon A Contact Lens: mean 85.70 versus 84.00 on control; difference 1.70 (95% CI -4.14 to 7.54), standardized effect d = 0.11; z-test p = 0.568.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Stenfilcon A Contact Lens and the control. The interval gives the range of effects that remain compatible with the data.

Subjective Scores on Comfort Before Removal

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Stenfilcon A Contact Lens: mean 79.30 versus 77.60 on control; difference 1.70 (95% CI -5.06 to 8.46), standardized effect d = 0.10; z-test p = 0.622.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Stenfilcon A Contact Lens and the control. The interval gives the range of effects that remain compatible with the data.

The posted secondary comfort summaries show group averages that are close, with intervals that include zero. Taken together, they do not present a clear pattern of separation between the two daily disposable lenses on the subjective comfort measures. The listed lens-centration outcomes address a different aspect of performance, but detailed results for every listed secondary measure are not available in the registry record.

This broad pattern is consistent with the primary comparison, where the mean insertion-comfort scores are also close and the interval includes zero. Consistency across related comfort measures can provide context, but it does not turn several uncertain estimates into proof of equivalence. Nor does it establish that any possible difference is unimportant; the registry record does not report a threshold for a meaningful difference.

Secondary results generally carry less weight than the primary outcome when many outcomes are examined, especially if no analysis hierarchy or multiplicity adjustment is reported. Testing multiple outcomes creates more opportunities for chance findings. The registry lists 21 outcome measures and 19 posted secondary outcomes, but multiplicity procedures and the prespecified status of each analysis are not reported. The secondary results should therefore be viewed as supporting context rather than definitive confirmatory evidence.

Some listed secondary outcome titles refer to comfort after the comfilcon A wear period, while the posted comparisons include overall comfort and comfort before removal after one week of test-lens wear. Those measures do not all represent the same time point or question. The registry record does not provide enough detail to reconstruct a complete analysis plan or determine how every listed endpoint relates to the primary hypothesis.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Subjective Scores on Overall Comfort After 4 Weeks of Comfilcon Use
• Subjective Scores on Overall Comfort
• Subjective Scores on Comfort Before Removal After 4 Weeks of Comfilcon Use
• Subjective Scores on Comfort Before Removal
• Number of Participants With Horizontal Lens Centration Grade
• Number of Participants With Horizontal Lens Centration Grade After 4 Weeks of Comfilcon A Wear
• Number of Participants With Horizontal Lens Centration Grade
• Number of Participants With Vertical Lens Centration Grade

9. Statistical Interpretation

10. Statistical Methods Explained

What does a group mean describe?

A mean is the arithmetic average of the recorded scores in a group. For the primary outcome, it summarizes participants’ reported comfort on insertion after one week of lens wear. A mean is useful for comparing groups, but it does not show whether all participants gave similar ratings or whether responses varied substantially. The standard deviation addresses that spread: a larger standard deviation indicates more dispersion of individual scores around the mean. It is not a confidence interval and does not indicate the range containing every participant’s score.

What is a mean difference?

The primary comparison is expressed as stenfilcon A minus somofilcon A. A positive estimate indicates a higher average score for stenfilcon A in this contrast, while a negative estimate would indicate a higher average score for somofilcon A. The reported estimate is 0.1 units. Because the scale runs from 0 to 100, the estimate is expressed in score units on that scale. The registry does not report a clinical-importance threshold for interpreting the size of this difference.

How should the interval be read?

An interval around an estimate represents uncertainty in the estimated contrast under the method used to construct it. A narrower interval indicates greater precision than a wider interval, all else being comparable. The primary interval extends from -4.805 to 5.005. Because it includes zero, the posted comparison is compatible with no difference as well as with modest differences in either direction. An interval does not guarantee that the true value lies within its limits, and its interpretation depends on the statistical method and confidence level. The confidence level and detailed method are not reported in the registry record.

What does the p-value add?

The unadjusted p-value for the primary comparison is 0.968. In general, a p-value measures how unusual the observed data, or data more extreme, would be under a specified null hypothesis and statistical model. It is not a measure of the size or importance of an effect, and it is not the probability that the null hypothesis is true. A p-value should be read alongside the estimated contrast and its interval. Here, the estimate is close to zero and the interval spans zero, so the p-value is consistent with the lack of a clear statistical separation in the posted comparison.

The word unadjusted matters because it indicates that the reported p-value is not described as corrected for testing multiple outcomes. The registry lists many outcome measures, but a multiplicity plan is not reported. Repeated testing can increase the chance of finding at least one apparently unusual result by chance. This is one reason to give greater weight to a prespecified primary outcome than to exploratory or unadjusted secondary findings.

Why does the crossover design matter?

In a crossover study, participants receive more than one study intervention in a planned sequence. Each person can contribute observations under both test conditions, so results from the same participant may be related. A statistical analysis can account for that dependence and may also consider period or sequence effects. Ignoring within-person correlation can affect the estimated uncertainty, while differences across periods or sequences can complicate interpretation. The registry describes randomized order and a crossover design, but does not report the model or methods used to address these features. The arm-level summary comparison should not be assumed to be a paired crossover analysis.

The reported counts for the primary outcome are 51 for somofilcon A and 52 for stenfilcon A. These summaries do not explain whether all participants completed both periods or how incomplete observations were handled. The record does not report the analysis population, missing-data methods, or a participant-flow description. Those omissions limit assessment of whether the posted results represent all randomized participants or a subset with available measurements.

What can the planning calculations tell readers?

The sample-size illustrations use the observed contrast as a planning reference and consider smaller fractions of that effect. They are not evidence about the trial’s original design and are not observed power. The calculations use a two-sided significance level of 0.05, equal allocation between groups, and a normal approximation. For the continuous outcomes, the figures are participants per arm. They illustrate that a smaller effect to detect requires more participants under the stated assumptions. The original protocol’s sample-size justification and design assumptions are not reported in the registry record.

In general, over-dispersion means that variability is greater than expected under a model’s assumptions. When variability is larger, estimates can be less precise and a study may need more participants to detect a given effect. The primary score summaries include standard deviations, but the registry does not report an over-dispersion assessment or a model that makes such an adjustment. This general concept should not be mistaken for a finding about this trial.

11. Confidence Intervals and Precision

The primary mean difference is 0.1 units, with an interval from -4.805 to 5.005. This range includes zero and extends in both directions, so the posted estimate does not tightly distinguish a small advantage for either lens from no difference. The interval is the main guide to precision: it shows uncertainty around the estimate rather than just its direction.

The group standard deviations are 12.6 for somofilcon A and 12.8 for stenfilcon A. These describe variation among individual comfort scores, whereas the interval concerns uncertainty in the between-lens mean difference. Keeping those concepts separate is important: participant-to-participant variability can be substantial even when group means are close, and a standard deviation is not a substitute for an interval around a comparison.

The registry does not report the confidence level or detailed procedure used to construct the interval, nor does it provide a paired crossover analysis description. The interval should therefore be interpreted as the posted comparison’s uncertainty summary, without assuming an unreported model. The record also gives no prespecified boundary for a difference that would be important to participants. Statistical precision and practical importance are related but distinct: an interval can describe uncertainty, but judging importance requires a meaningful threshold that is not reported in the registry record.

12. 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 event counts. They use the observed effect as a reference and also consider planning for 75% of the observed effect and 50% of the observed effect. 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 original trial’s sample-size assumptions and justification are not reported in the registry record.

The 80% power column gives the number of participants per arm that the planning calculation estimates would be needed for an 80% chance of detecting the stated effect under its assumptions, if that effect were the true one. The 90% power column gives the corresponding planning number for a 90% chance. These are design illustrations, not descriptions of the enrolled trial’s ability to detect an effect after the fact.

The figures increase as the target effect becomes smaller: a smaller difference is harder to distinguish from random variation, so the planning calculation calls for more participants. The listed values are especially sensitive when the observed effect used as the starting reference is small. They should not be treated as a recommendation for a future study without a separately justified target effect and design.

These calculations are not observed power. They do not show the probability that the completed trial detected a real effect, and they do not change the interpretation of the posted estimate and interval. The registry record does not report whether its original planning used the same assumptions or methods.

13. 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 = 0.100; pooled standard deviation σ = 12.701.
2. n = 2 × (1.96 + 0.842)² × 12.701² / 0.100² = 253,244.3, rounded up to 253,245 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 <- 0.100000000000009                      # observed difference in means
sigma <- 12.7013837244157                     # 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(4005885)
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 = 253,245 (80% power), 339,023 (90% power)
 75% of observed effect: n per arm = 450,213 (80% power), 602,707 (90% power)
 50% of observed effect: n per arm = 1,012,978 (80% power), 1,356,090 (90% power)
power.t.test: 253245.3 
Simulated power at n = 253,245 per arm: 0.804 (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.

14. Multiplicity, Missing Data and Analysis Populations

The registry record lists 21 outcome measures and 19 posted secondary outcomes. It does not report a multiplicity adjustment, a testing hierarchy, or a plan specifying which secondary comparisons were confirmatory and which were exploratory. When many outcomes are tested, the chance of at least one apparently notable result can increase even if no corresponding effect exists. Adjustment or a prespecified hierarchy can help control how results are interpreted, but no such approach is described in the registry record.

The primary comparison has an unadjusted p-value. The posted secondary comparisons are also described with unadjusted p-values. They should not be interpreted as though the number of outcomes tested had no bearing on evidential strength. The registry record does not report a broader statistical analysis plan or explain whether any analyses were conducted but not posted.

Missing-data handling is not reported in the registry record. The primary outcome summaries include 51 participants for somofilcon A and 52 for stenfilcon A, while enrollment is 55. The record does not explain the difference between those counts, whether participants contributed data under both test lenses, or how incomplete observations were treated. The specific analysis population—such as all randomized participants or participants with available measurements—is also not reported.

These details matter especially in a crossover study, where a participant may have data for one lens period but not the other. Without the analysis population, missing-data approach, and model specification, readers cannot determine whether the posted comparison accounts for within-person dependence or whether missing observations could affect the result. The registry record also does not report interim analyses or other monitoring details; no conclusions about those procedures can be drawn from the available record.

15. Safety Results

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

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 5% reporting threshold.

The registry records zero participants affected by serious adverse events among 55 at risk in the comfilcon A group, 53 at risk in the somofilcon A group, and 53 at risk in the stenfilcon A group. It also records zero participants affected by other adverse events in each of those groups, using the same at-risk counts, and zero deaths in every group. No serious adverse-event terms are listed.

These figures describe the adverse-event counts recorded for this trial; they do not establish that no events could occur or that the lenses have no risk. The study enrolled 55 participants and used one-week periods for each test lens after a month of comfilcon A wear. The registry record does not give further detail on event definitions, surveillance, or the timing of adverse-event collection. The counts should be interpreted within the scope of the recorded study and not generalized to other settings or durations.

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

The posted results describe similar average comfort-on-insertion scores for somofilcon A and stenfilcon A after one week in this study. The estimated mean difference is small, and its interval includes zero. This means the summary comparison does not establish a clear difference in average scores. It does not prove the lenses produce identical experiences, and it does not establish equivalence or non-inferiority: the registry record does not report a prespecified equivalence margin or non-inferiority design.

The comparison concerns subjective ratings from existing comfilcon A monthly-lens wearers after a particular refit and wear sequence. It does not answer every question about lens performance, longer-term use, other populations, or outcomes not recorded in the registry. Comfort on insertion is only one measure, and the registry’s other listed comfort and centration measures should not be conflated with the primary endpoint.

The study’s crossover structure means participants wore both test lenses in randomized order, but the posted comparison does not describe a model accounting for paired measurements or period effects. The analysis population, missing-data methods, and detailed statistical plan are also not reported. These gaps limit how fully the numerical comparison can be evaluated.

The adverse-event figures record no affected participants or deaths in the listed groups, but the counts do not show that risk is absent. The registry’s results are one set of observations from this completed study. They do not, on their own, establish a broader treatment or safety conclusion beyond the recorded participants, lenses, schedule, and outcomes.

17. Why This Trial Matters Statistically

This trial is a useful example of why design labels matter when reading a statistical comparison. A crossover design assigns participants to sequences of more than one lens, so the two sets of observations may be related within individuals. Arm-level means and standard deviations are informative summaries, but they do not reveal whether the inferential comparison used that within-participant structure. The registry record does not report the analysis method needed to resolve that question.

The result also illustrates the distinction between an estimate and its uncertainty. The primary mean difference is close to zero, while the interval spans values on either side of zero. Reading the estimate alone could suggest a precise answer; considering the interval shows that uncertainty remains. Conversely, a large p-value should not be treated as evidence that two lenses are exactly alike.

Planning illustrations based on a small observed effect can call for very large participant counts, even though the completed trial enrolled 55 participants. That contrast is a statistical feature of planning around the observed effect, not a retrospective judgment that the trial had adequate or inadequate power. The original design assumptions are not reported.

Finally, the registry lists multiple outcomes but does not report multiplicity handling, missing-data methods, or the full analysis population. Such omissions are important for interpreting secondary findings and for understanding how much weight to place on the posted comparisons. The example emphasizes the value of reading outcomes, design, uncertainty, and reporting detail together.

18. Limitations

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

The registry record does not report a full statistical analysis plan, including whether the primary comparison accounted for the crossover structure, within-participant correlation, period, or sequence. The posted summaries are arm-level, and the available comparison does not make clear how repeated observations were handled. This is a particular interpretive limitation for a study in which participants were randomized to sequences of both test lenses.

The primary outcome counts are 51 and 52, compared with enrollment of 55, but the registry does not provide participant flow, reasons for missing measurements, or the analysis population. It does not explain whether participants contributed complete data for both test lenses. Missing-data methods are not reported, so the potential influence of incomplete observations cannot be assessed.

The record also does not report a threshold for a clinically meaningful comfort-score difference, a confidence level or detailed interval-construction method, a multiplicity plan, or the original sample-size justification. Although many outcome measures are listed, the full set of results and analysis details are not described. The registered wear schedule is limited to the specified refit and short test-lens periods; the record does not provide results for longer-term use.

These limitations do not change the posted values, but they restrict what can be concluded from them. In particular, the results should not be described as demonstrating equality, equivalence, or absence of risk.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: A Clinical Comparison of Two Daily Disposable Soft Contact Lenses — NCT04005885.
• Registry record last updated 2021-01-05; status last verified 2020-12.
• Results first posted 2020-12-11.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

22. Record Summary

NCT04005885 is a completed randomized, double-masked crossover study comparing somofilcon A and stenfilcon A daily disposable contact lenses in existing comfilcon A monthly-lens wearers with myopia. The registry records enrollment of 55 participants and a sequence in which each test lens was worn for 1 week after a month of comfilcon A use.

The primary outcome was subjective comfort on insertion after one week. Mean scores were 90.3 for somofilcon A and 90.4 for stenfilcon A; the posted mean difference was 0.1, with an interval from -4.805 to 5.005 and an unadjusted p-value of 0.968. The interval includes zero, and the registry does not report a threshold for a meaningful difference.

Important analysis details—including crossover modeling, missing-data handling, analysis populations, and multiplicity procedures—are not reported in the registry record. Recorded serious and other adverse-event counts and deaths were zero in the listed groups.