Clinical Evaluation on Using Personal Face Masks With Spectacles Versus Contact Lenses: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Clinical Evaluation on Using Personal Face Masks With Spectacles Versus Contact Lenses (NCT04658797), a randomized na study. The primary outcome is Visual Acuity - High Contrast.

2. Clinical Question

3. Trial Design

This completed clinical study used randomized allocation and a parallel design, with no masking. The registry lists 30 participants enrolled. The arm descriptions identify daily disposable contact lenses and single-vision spectacles as the vision-correction approaches being compared. The study summary describes spectacle wearers randomized either to continue wearing spectacles or to be fitted with daily disposable contact lenses.

The listed intervention was somofilcon A daily disposable contact lenses in the contact-lens arm and single-vision spectacles in the spectacle arm. A personal facemask is also listed as an intervention. The registry record does not provide further detail about the mask-use procedures or the way mask use was incorporated into the assessment.

The study started on 2020-11-01, and the primary completion date was 2021-04-15. Its status is completed. The phase is listed as NA. CooperVision, Inc. is the listed sponsor. The condition recorded is myopia.

The primary outcome is baseline high-contrast visual acuity, not a change from baseline or a later follow-up measurement. The record lists 33 outcome measures, but it does not post secondary results. The study summary emphasizes satisfaction with vision correction and ease of use of personal face masks; those outcomes are not reported in the registry record. Details such as eligibility criteria, follow-up procedures, and the original design assumptions are also 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.

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 Visual Acuity - High Contrast, measured over Baseline.

The primary endpoint is high-contrast visual acuity measured with a logMAR visual acuity chart. The registry identifies the outcome as a mean with standard deviation and gives the timeframe as baseline. It is therefore a description of visual acuity at baseline in each assigned arm, not a comparison of change over time.

Visual acuity is a clinical measurement of how clearly a person can see under specified testing conditions. High-contrast testing uses clearly defined visual targets against a contrasting background. LogMAR is a scale used to express visual acuity; as a general interpretation, lower logMAR values correspond to better acuity.

This endpoint gives a quantitative measure of vision at the time of baseline assessment. It does not directly measure satisfaction with vision correction, comfort, or ease of using a personal face mask. Those topics appear in the study’s stated aim, but related results are not reported in the registry record. The baseline means were -0.06 logMAR for the contact-lens arm and -0.07 logMAR for the spectacle arm, with standard deviations of 0.07 and 0.05, respectively.

7. Results Posted in the Registry

• Single Vision Spectacle for Vision Correction: mean -0.07 versus -0.06 on control; difference -0.01 (95% CI -0.05 to 0.03), standardized effect d = -0.16; z-test p = 0.653.

8. Statistical Interpretation

9. Statistical Methods Explained

The outcome is continuous: visual acuity is recorded numerically on a logMAR scale. The registry reports the mean and standard deviation for each arm. A mean describes the group’s average value. A standard deviation describes how spread out individual measurements are around that group average. These statistics answer different questions: the mean describes the location of the measurements, while the standard deviation describes their variability.

What does the mean difference describe?

The comparison is a mean difference, with the spectacle arm compared against the daily disposable contact-lens arm. The posted estimate is -0.01 logMAR. In general, a mean difference expresses the distance between group averages in the measurement’s original units. Its sign depends on the order of the groups in the comparison. Here, the registry gives the group means as -0.07 logMAR for spectacles and -0.06 logMAR for contact lenses, and labels the comparison as spectacles relative to contact lenses.

A difference in means does not itself indicate whether the difference is important to participants or clinically meaningful. That interpretation depends on context, including what size of difference would matter and how the measurement was collected. Such a threshold is not reported in the registry record. The numerical result should therefore be described as the observed difference in group averages, without assigning it a clinical meaning that the record does not establish.

How should the p-value be read?

The reported unadjusted p-value is 0.653. In general, a p-value describes how compatible the observed data are with a specified null model, under the assumptions of the statistical test. It is not the probability that the null hypothesis is true, nor does it measure the size or importance of a difference. The registry does not report the full statistical test specification, so the p-value should be read as the posted unadjusted result rather than as evidence of a more detailed analysis than the record documents.

The p-value does not replace the estimated mean difference or its confidence interval. The estimate describes the direction and size of the observed contrast; the interval communicates uncertainty around that estimate. A result that does not meet a conventional significance threshold does not prove that the groups are identical. It can also occur when data are too limited to distinguish a modest difference from no difference.

Why does variability matter?

Participants within an arm may have different acuity measurements. Standard deviations summarize this within-arm spread. Greater variation generally makes it harder to estimate a group mean precisely, while less variation can support a more precise estimate, all else being equal. The registry reports standard deviations of 0.07 for contact lenses and 0.05 for spectacles. Those summaries describe the observed spread, but they do not explain its sources or show the distribution of individual measurements.

In general, over-dispersion means that observed variability is greater than expected under a model. When a model fails to account for that extra variability, its uncertainty estimates can be too small and its inferential results can be misleading. The registry record does not report an over-dispersion assessment or a model that would require such an assessment. This concept is relevant as a general statistical consideration, not as a claim that over-dispersion occurred in this study.

The comparison is described as unadjusted. An adjusted analysis can account for specified covariates, but the record does not report such an analysis or identify adjustment variables. The registry also does not report the exact statistical test, handling of any missing measurements, assumptions checked for the primary analysis, or a prespecified analysis plan. These omissions limit what can be concluded about the analytic details beyond the posted summary statistics.

Randomization describes how participants were allocated, whereas the mean difference and p-value describe the outcome data. The registry lists randomized allocation, but does not report allocation-concealment procedures. Masking is listed as none. In general, lack of masking can affect outcomes that depend on participant or assessor judgment; visual acuity is measured with a chart, but the record does not say whether assessors were masked or describe quality-control procedures. No assumptions about those procedures should be inferred.

10. Confidence Intervals and Precision

The estimated baseline mean difference is -0.01 logMAR, comparing spectacles with daily disposable contact lenses. The registry reports a confidence interval whose lower endpoint is negative and whose upper endpoint is positive; it therefore includes zero. The interval allows for uncertainty in the estimated difference in both directions rather than fixing the result at the observed mean difference.

In general, a confidence interval gives a range of values compatible with the data under the method used to construct it. A narrower interval indicates greater precision, while a wider interval indicates less precision. The registry’s interval spans zero, so the posted result does not rule out no difference in baseline mean acuity. It also allows for differences in either direction. The interval is more informative about uncertainty than the point estimate alone.

The arm sizes for this outcome are 15 participants each. Those group sizes help explain why the result should be read with attention to uncertainty, but they do not by themselves determine the interval width; variability and the analysis method also matter. The registry provides standard deviations for both arms and an unadjusted p-value of 0.653. It does not report a clinically important threshold for logMAR differences, so the precision of the estimate cannot be translated into a judgment about whether a difference would matter to participants.

Because the endpoint is measured at baseline, this interval concerns the difference between baseline group means. It does not quantify uncertainty about a change from baseline or a later treatment effect. Nor does it provide precision information for satisfaction or ease-of-use outcomes, which are not 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 estimates are participants per arm, not total events. They are illustrations based on the observed effect, not the original design assumptions for this trial; those original assumptions are not reported in the registry record. The planning calculation uses a two-sided significance level of 0.05, equal allocation between the arms, and a normal approximation. The effect to detect is set to the stated fraction of the observed effect.

For planning at 100% of the observed effect, the estimate is 581 participants per arm for 80% power and 778 participants per arm for 90% power. At 75% of the observed effect, the estimates are 1,033 participants per arm for 80% power and 1,383 participants per arm for 90% power. At 50% of the observed effect, the estimates are 2,324 participants per arm for 80% power and 3,111 participants per arm for 90% power.

In plain terms, the 80% power column represents the planning size associated with an 80% chance of detecting the specified effect under the calculation assumptions if that effect is truly present. The 90% power column uses a higher target chance of detection. These are planning illustrations, not observed power. Smaller effects require more participants because they are harder to distinguish from random variation. The estimates depend on the observed effect and the stated assumptions; they are not evidence that the original trial was designed with these targets.

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 = -0.010; pooled standard deviation σ = 0.061.
2. n = 2 × (1.96 + 0.842)² × 0.061² / -0.010² = 580.8, rounded up to 581 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 <- -0.01                      # observed difference in means
sigma <- 0.0608276253029822                     # 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(4658797)
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 = 581 (80% power), 778 (90% power)
 75% of observed effect: n per arm = 1,033 (80% power), 1,383 (90% power)
 50% of observed effect: n per arm = 2,324 (80% power), 3,111 (90% power)
power.t.test: 581.8 
Simulated power at n = 581 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 33 outcome measures, but reports no posted secondary results. It also records no analysis entries. The primary outcome is baseline high-contrast visual acuity; the record does not identify a multiplicity procedure for interpreting results across outcomes. Multiplicity arises when several outcomes or comparisons are tested, because interpreting many tests can increase the chance of findings that appear notable by chance. Without a reported analysis plan or correction method, the registry does not establish how multiple outcomes were prioritized or handled.

The study summary states that satisfaction with vision correction and ease of use of personal face masks were aims. However, results for those measures are not reported in the registry record. The available primary result should not be treated as a substitute for those unreported outcomes, because visual acuity and satisfaction or ease of use measure different aspects of experience.

The record does not report missing-data counts, reasons for missingness, or a method for handling missing observations. It also does not identify the analysis population, such as whether the primary analysis included everyone randomized or only participants with an available measurement. The reported arm sizes are 15 for each group, but those counts alone do not describe whether any measurements were missing or how missing values were handled.

Without the analysis population and missing-data methods, it is not possible to determine from the registry whether the posted means include all randomized participants or a subset. The record also does not report a protocol-level statistical analysis plan, prespecified hierarchy of outcomes, or interim analysis procedures. These details are not reported in the registry record, so they should not be inferred from the posted p-value or outcome summaries.

14. 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 lists 15 participants at risk for serious adverse events in the spectacle arm and 15 in the daily disposable contact-lens arm. It records 0 participants affected by serious adverse events in each arm. The listed counts for other adverse events affected are also 0 in both arms, and deaths are recorded as 0 in each arm. No serious adverse event terms are listed.

These are the safety figures reported in the registry record. A zero count means that no events of the listed type were recorded in these results; it does not establish that the risk is absent. The record does not describe the adverse-event collection procedures, reporting period, or completeness of ascertainment. The counts should therefore be read as registry-reported observations, not as proof that no adverse events could occur.

The safety figures do not provide a comparative estimate of risk beyond the counts listed. The registry does not report an inferential safety analysis or further detail on event severity or relatedness. No conclusion about safety outside the scope of these recorded counts follows from the posted information.

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

The posted primary result describes baseline high-contrast visual acuity in participants assigned to daily disposable contact lenses or single-vision spectacles. The group means were -0.06 and -0.07 logMAR, respectively, and the mean difference for spectacles relative to contact lenses was -0.01 logMAR. The confidence interval includes zero, and the unadjusted p-value is 0.653. Taken together, these data do not establish a clear baseline difference between the groups.

This finding does not establish that the approaches are equivalent. Demonstrating equivalence requires a defined margin and an analysis designed to assess whether differences fall within that margin; neither is reported in the registry record. A non-significant result is also not proof that there is no difference. It indicates that the posted data do not provide strong evidence of a difference under the reported comparison.

The endpoint is measured at baseline. It does not show the effect of assignment on a later outcome, nor does it address changes in visual acuity. The registry’s stated aim includes satisfaction with vision correction and ease of using a personal face mask, but those results are not reported in the registry record. Accordingly, the baseline acuity result cannot answer whether participants found either approach more satisfactory or easier to use with a mask.

The record describes randomization, but does not report the detailed statistical plan, missing-data methods, or analysis population. These gaps constrain interpretation of the posted summary. The result is best understood as a descriptive baseline comparison with an unadjusted statistical comparison and uncertainty that includes both positive and negative differences. It should not be generalized beyond the outcomes and information recorded in this trial.

16. Why This Trial Matters Statistically

This trial is statistically instructive because its stated aim and its posted primary endpoint address different kinds of questions. The summary emphasizes satisfaction with vision correction and ease of use of personal face masks, while the primary outcome is baseline high-contrast visual acuity. A quantitative acuity measure can describe vision under a specified test condition, but it does not directly measure satisfaction or ease of use. Keeping those outcome concepts distinct prevents the primary result from being used to answer an unreported question.

The endpoint is recorded at baseline, which is also important for interpretation. A randomized design can support comparisons of outcomes after assignment, but a baseline measurement is a description of groups at the start of the assessment rather than an estimate of subsequent change. The posted means and mean difference therefore need to be read in relation to their stated timeframe.

The result also illustrates why a point estimate, confidence interval, and p-value should be considered together. The mean difference is -0.01 logMAR, the interval includes zero, and the unadjusted p-value is 0.653. The estimate alone does not communicate its uncertainty, while the p-value alone does not communicate the size of the difference. The interval makes clear that the posted data are compatible with differences in either direction.

Finally, the registry lists no posted secondary results, despite the study summary’s emphasis on satisfaction and mask-use experience. That distinction matters: outcome aims and outcome results are not interchangeable. Reporting the outcomes relevant to the study question, along with analysis and missing-data details, is important for readers assessing what the evidence can and cannot address.

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 provides a limited account of the study procedures and analysis. It identifies randomized allocation, a parallel design, and no masking, but does not report allocation-concealment methods, participant eligibility details, or the assessment procedures beyond naming a high-contrast logMAR visual acuity chart. The record does not state whether outcome assessors were masked.

The primary outcome is reported at baseline rather than as a follow-up value or a change from baseline. This limits the result to a comparison of baseline group means and does not quantify an outcome after participants followed their assigned vision-correction approach. The study summary focuses on satisfaction and ease of using personal face masks, but those outcomes are not reported in the registry record.

The analysis description is also limited. The registry does not report the statistical test specification, an analysis plan, the analysis population, missing-data methods, or a clinically important threshold for the acuity scale. Although arm sizes and summary statistics are posted, the record does not provide individual-level distributions or explain how the observations were collected and checked.

Masking is listed as none, and the record does not clarify which people involved in the assessments knew the assigned approach. The safety counts are reported without detail about event collection procedures, reporting periods, or completeness. These limitations do not change the posted numbers, but they narrow the conclusions that can be drawn from them.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Clinical Evaluation on Using Personal Face Masks With Spectacles Versus Contact Lenses — NCT04658797.
• Registry record last updated 2021-10-20; status last verified 2021-09.
• Results first posted 2021-10-20.
• 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

NCT04658797 is a completed randomized, parallel study sponsored by CooperVision, Inc. It enrolled 30 participants and compared daily disposable contact lenses with single-vision spectacles among spectacle wearers. Masking is listed as none, and the phase is listed as NA. The recorded condition is myopia.

The primary outcome is baseline high-contrast visual acuity measured in logMAR. The reported group means are -0.06 for contact lenses and -0.07 for spectacles; the mean difference is -0.01, with an unadjusted p-value of 0.653. The confidence interval includes zero. No secondary results are posted in the registry record, and satisfaction and ease-of-use results are not reported. Serious adverse events, other adverse events, and deaths are recorded as 0 in both arms.