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

1. Trial at a Glance

This page covers the registry results for Comparison of Two Daily Disposable Soft Contact Lenses (NCT03779503), a randomized na study. The primary outcome is Lens Fit - Horizontal Centration.

2. Clinical Question

In broad terms, the study set out to examine short-term clinical performance and subjective acceptance of two daily disposable lenses. The brief summary describes that aim, while the registered primary outcome focuses specifically on the horizontal position of the lens on the eye. These are related but distinct questions: a lens-fit assessment is not itself a complete measure of subjective acceptance, and the presence of registered subjective outcomes does not supply their results.

The registry also lists Subjective Score for Vision twice among the secondary outcomes. It does not explain whether these entries represent different assessments, time points, or duplicated labels. The exact question, scoring scale, and comparison intended for those outcomes are not reported in the registry record.

3. Trial Design

The study is listed as randomized, double-masked, and crossover, with enrollment of 55. It compares two devices: midafilcon A and somofilcon A. In a crossover design, a participant receives each study treatment in separate periods, so comparisons can be made within the same participant. This can reduce the influence of stable differences between participants, but it also makes period, sequence, and carryover considerations relevant to interpretation.

The registry arm descriptions state that participants would be randomized to wear each lens for one week of daily wear during the study. The record does not describe the order in which lenses were worn, how randomization sequences were generated or concealed, whether a washout period was used, or how the study handled changes between lenses. Those details are important for understanding whether the period with one lens could affect observations during the period with the other.

Double masking is recorded, but the registry does not identify which study personnel or participants were masked, nor how masking was maintained for visibly or perceptibly different lenses. The record lists the study as completed and gives a start date of 2019-02-08 and a primary completion date of 2019-07-30. The phase is listed as NA.

The primary measure is described as a baseline assessment of horizontal centration. The registry does not clarify how a baseline assessment aligns with the crossover periods or identify whether separate assessments were planned for each lens period. This limits the ability to reconstruct the intended comparison from the registration alone.

The record lists 10 outcome measures and zero analysis entries. The absence of analysis entries does not show that no analyses were conducted; it means the registry record does not include analysis-level results. It also does not give a statistical analysis plan, a sample-size justification, or details of the planned model. These omissions matter because crossover studies can require methods that account for within-participant correlation, treatment sequence, and period effects.

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.

First Intervention

Reasons for not completing this period:

Second Intervention

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 Lens Fit - Horizontal Centration, measured over Baseline.

The primary endpoint is titled “Lens Fit - Horizontal Centration.” It assesses the horizontal position of a lens, using the categories extremely nasal, slightly nasal, optimum, slightly temporal, and extremely temporal. The unit is recorded as percentage of lenses, and the timeframe is baseline.

Lens centration is a descriptive aspect of fit: the categories indicate where the lens sits relative to the eye’s horizontal center. Recording the distribution across ordered categories can show whether lens positions tend toward nasal or temporal placement and how often the position is judged optimum. The registry record does not report the category frequencies, the criteria used to assign categories, or a threshold for a clinically meaningful difference.

General statistical context: a categorical endpoint preserves distinctions among the possible fit assessments. Reducing those categories to one value or one contrast requires an explicit analysis choice, such as comparing the full distribution or defining a particular category as favorable. Different choices answer different questions, and the registry does not report such a reduction or a single comparison for this endpoint.

The baseline timeframe also needs context. The registry does not explain whether baseline means before either lens was worn, after a fitting procedure, or a particular point in a crossover sequence. Nor does it report separate results by lens. Without those details and the observed category counts, the endpoint description identifies what was intended to be measured but does not establish the comparative findings.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Randomization assigns participants to treatment sequences by chance, aiming to reduce systematic differences between groups or sequences. Here, randomization is recorded and the study is described as a crossover. The registry does not report the sequence-generation method, allocation concealment, or the number of participants assigned to each sequence. These details would help assess how assignment was implemented and whether selection could have influenced sequence allocation.

What does crossover mean statistically?

General statistical context: in a crossover study, each participant receives more than one intervention in different periods. A comparison can use the participant as their own control, which can account for characteristics that remain stable over the study. Observations from the same participant are correlated rather than independent. An analysis that treats all observations as independent can misstate uncertainty because it does not account for that within-participant relationship.

Crossover designs also require attention to period and sequence. A period effect is a change associated with when an observation is made, rather than with the lens itself. A sequence effect may arise if the order of the lenses matters. Carryover occurs when the effect of one period persists into the next. These are general design considerations, not reported findings about this study. The registry does not describe a washout, report period-specific results, or specify whether these effects were assessed.

How should a categorical endpoint be analyzed?

The primary outcome is a set of five horizontal-centration categories, reported as a percentage of lenses. General statistical context: categorical outcomes can be summarized by counts or proportions in each category. If the categories are ordered, an analysis may use their ordering, but that requires an explicit model and assumptions about how category spacing should be treated. Another approach could compare the overall distribution without assuming equal distances between categories. The registry does not report which approach was planned or used.

For a crossover comparison, the analysis would also need to account for repeated observations within participants if both lenses contribute outcomes. The record does not report the statistical model, the unit of analysis, or how multiple lenses or eyes per participant were handled. It therefore is not possible to infer whether the intended analysis used a paired comparison, a repeated-measures model, or another method.

What do masking and allocation establish?

The registry design labels are randomized and double-masked. General statistical context: random allocation and masking can reduce some forms of bias, but the labels alone do not explain their implementation. Masking can limit the influence of expectations on assessments, while randomization can reduce systematic assignment differences. The registry does not identify who was masked, how masking was maintained, or whether assessors were masked when judging centration. These implementation details are not reported in the registry record.

What can be said about precision and planning?

General statistical context: precision is commonly communicated with an uncertainty interval around an effect estimate. More precise estimates generally have narrower intervals, while less precise estimates have wider intervals. The registry gives no primary-outcome estimate or interval, so precision cannot be assessed from its results. Nor does it report a sample-size justification or the assumptions used when planning enrollment.

A planning illustration based on an observed effect is not an observed result and is not the trial’s own sample-size justification. Such an illustration depends on assumptions about the target effect, significance level, allocation, and statistical model. The stated planning convention uses a two-sided significance level of 0.05, equal allocation, and a normal approximation; the effect to detect is defined as a stated fraction of the observed effect. For non-time-to-event outcomes, the convention describes participants per arm. These assumptions do not establish that the trial was designed with those assumptions or that it had a particular probability of detecting an effect.

In general, over-dispersion occurs when outcome variability exceeds what a chosen statistical model expects. If present, ignoring it can produce uncertainty estimates that are too small. The registry does not report evidence of over-dispersion or an analysis model for the categorical endpoint; this is a general consideration, not a claim about the study data.

What analysis details are absent?

The record contains zero analysis entries. It does not report an analysis plan, model specification, covariates, handling of missing values, adjustment for multiple outcomes, or treatment of protocol deviations. It also does not give outcome estimates or tests. Without those details, readers cannot reproduce or evaluate an inferential analysis from the registry record. These gaps limit interpretation but do not establish that the investigators did not perform analyses outside the registry.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists 10 outcome measures, including Subjective Score for Vision twice, and gives zero analysis entries. It does not specify which outcomes were primary or secondary beyond the recorded primary measure and secondary-outcome list, nor does it explain why the subjective outcome label appears twice. The exact outcome definitions, assessment times, and planned contrasts are not reported in the registry record.

General statistical context: when several outcomes or comparisons are tested, the chance of at least one apparently notable result can increase if each test is interpreted separately. A prespecified multiplicity strategy can help control that risk, but the registry does not report one. No conclusion about whether any correction was used can be drawn from the record.

The registry does not report missing outcome counts, reasons for missingness, or how incomplete observations were handled. It also does not define an analysis population, such as whether analyses were intended to follow randomized assignment or include only participants with measurements under both lenses. These choices can affect which observations contribute to a crossover comparison and how results should be interpreted.

General statistical context: missingness can be related to observed or unobserved characteristics, and different assumptions about that process can lead to different estimates. Complete-case analyses, imputation, and model-based approaches rely on different assumptions. No method can be attributed to this study from the registry record.

The record also does not report deviations from the assigned lens sequence, exclusions, or protocol adherence. Without this information, it is not possible to determine how the analysis population related to the randomized participants or to assess the sensitivity of results to missing data and deviations.

11. 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 zero serious adverse events and zero deaths in each lens group. It also lists zero other adverse events in each group. The listed number at risk is 55 for Midafilcon A and 55 for Somofilcon A for both serious and other adverse events.

These are registry-recorded counts, not estimates of comparative safety. The record does not provide event descriptions, event timing, severity categories beyond the serious-versus-other distinction, or an analysis comparing the lenses. It also does not explain how adverse events were collected or whether the at-risk counts represent exposure during the crossover periods or another reporting convention.

General statistical context: observing no recorded events does not prove that the underlying event risk is zero. The strength of a safety conclusion depends on the number of observations, exposure duration, event definitions, completeness of follow-up, and the precision of an estimate. No uncertainty interval or formal safety comparison is reported in the registry record.

Because this was a crossover study and both lens groups have a listed at-risk count of 55, those group counts should not be added to infer the number of distinct participants. The record does not describe whether the same participants contributed safety information during both lens periods. The adverse-event entries therefore should be read as the counts recorded for each listed group, not as a basis for a broader claim that either lens is free of risk.

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

The registry record establishes that a randomized, double-masked crossover study compared midafilcon A and somofilcon A, with each described for one week of daily wear. It identifies a primary lens-fit measure and states that the study aimed to examine short-term clinical performance and subjective acceptance. These registry entries describe the design and purpose; they are not a report of comparative effectiveness.

The primary outcome is a distribution across horizontal-centration categories, but the registry does not report category results or reduce the outcome to one comparison. No estimate, confidence interval, or test result is available for that endpoint. The record therefore does not show the direction or size of a difference, or how precisely any difference was estimated.

Likewise, the listed subjective vision outcome does not come with scores or a defined comparison. The registry’s safety entries show zero recorded serious adverse events, zero recorded other adverse events, and zero deaths in each listed lens group. Those entries are limited to the registry counts and do not establish that adverse events could not occur or provide a comparative risk estimate.

General statistical context: a lack of a statistically significant result, if one had been reported, would not by itself establish equivalence. Equivalence requires a prespecified margin and an analysis showing that uncertainty is sufficiently contained within that margin. Neither an equivalence objective nor an equivalence analysis is reported in the registry record. Similarly, a planning calculation is not evidence about an observed treatment effect.

The record does not support a claim that one lens is superior, that the lenses perform identically, or that either lens is safer. It supports a narrower conclusion: a completed study was registered with a crossover comparison and specified outcomes, while the registry record does not include analysis results needed to judge comparative findings.

13. Why This Trial Matters Statistically

This trial is statistically notable because a crossover design compares lenses within participants rather than relying only on comparisons between separate groups. General statistical context: this structure can make efficient use of participant information when measurements are available under each intervention and when period and carryover effects are appropriately handled. It also creates analytic requirements that differ from those of a simple parallel-group trial.

The endpoint adds another important issue: horizontal centration is recorded in multiple categories, not as a single continuous measurement or a single reported contrast. The categories preserve detail about nasal and temporal placement, but an inferential comparison must define what aspect of that distribution is being tested. The registry record does not provide the reduction or model needed to interpret one comparative result.

The listed design features—randomization and double masking—are relevant to the credibility of measurements, particularly for an assessment that may involve judgment. Yet design labels are not substitutes for implementation details. The record does not identify who was masked or describe how the crossover sequence was managed.

The study also illustrates the difference between registering outcomes and reporting analyses. Ten outcome measures are listed, but zero analysis entries appear in the registry record. Without outcome estimates, uncertainty measures, and analysis methods, readers cannot assess effect size, precision, multiplicity, or the handling of incomplete data. The issue is not merely the absence of a p-value; the underlying results and their analysis are not available in the registry record.

For biostatistical interpretation, the central lesson is to separate design information from evidence about outcomes. The record specifies a comparative question and a categorical endpoint, but it does not provide the results needed to answer that question. A careful reading avoids turning an intended comparison or a zero event count into a broader conclusion than the recorded data support.

14. 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 does not report the observed results for the primary lens-fit outcome. It provides neither category-specific percentages nor a defined single comparison, and it does not include estimates of uncertainty. This is the most direct limitation for interpreting the comparative question.

The crossover description is incomplete for statistical evaluation. Although the arm descriptions specify one week of daily wear for each lens, the record does not give treatment sequence details, any washout arrangements, period-specific assessments, or an analysis of possible carryover. It also does not report how repeated measurements within participants were modeled.

The primary outcome is described at baseline, but the record does not clarify how that timeframe relates to the lens periods. It does not provide operational criteria for assigning the five centration categories or specify whether assessments were made for one or both eyes. The unit is percentage of lenses, but the underlying number of lens assessments and the denominator for any outcome are not reported.

Other limitations include the absence of an analysis plan, sample-size justification, analysis population, missing-data methods, and multiplicity strategy. The registry lists Subjective Score for Vision twice, without explaining whether the entries differ. It also does not report results for these or the other registered outcomes.

The safety entries contain event counts but no event details, follow-up completeness, or uncertainty estimates. The registry record does not explain the relationship between the at-risk counts and crossover exposure. These limitations mean that the listed zero counts should be interpreted narrowly, not as a definitive comparative safety assessment.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Comparison of Two Daily Disposable Soft Contact Lenses — NCT03779503.
• Registry record last updated 2020-10-08; status last verified 2020-09.
• Results first posted 2020-10-08.
• 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.

18. Record Summary

The registry record describes a completed randomized, double-masked crossover study of midafilcon A and somofilcon A daily disposable soft contact lenses in people with bilateral astigmatism. Enrollment was 55. The arm descriptions specify one week of daily wear for each lens. The study dates are 2019-02-08 for start and 2019-07-30 for primary completion.

The primary outcome is baseline horizontal centration, expressed as percentage of lenses across five nasal-to-temporal categories. The registry lists 10 outcome measures, including Subjective Score for Vision twice, and zero analysis entries. It does not report a reduced primary comparison, outcome results, statistical methods, or missing-data handling.

The listed serious adverse events, other adverse events, and deaths are zero in each lens group. These registry counts do not establish a comparative safety estimate. Overall, the record documents the design and intended measurements but does not report the analyzed results required to assess comparative lens fit, subjective vision, or precision.