The Clinical Comparison of Narafilcon A and Stenfilcon A Contact Lenses: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The Clinical Comparison of Narafilcon A and Stenfilcon A Contact Lenses (NCT02920970), a randomized na study. The primary outcome is Ocular Physiology.

2. Clinical Question

The study’s stated aim was to compare clinical performance and subjective acceptance of the two lenses under daily-wear, daily-disposable use. The record identifies ocular physiology as the primary outcome, but it does not specify a single summary result for that comparison. It also does not provide a detailed definition of subjective acceptance or identify a particular acceptance measure among the outcomes.

In general, a crossover design compares conditions within participants across different periods, rather than assigning each participant to only one condition throughout. That design can make within-participant comparisons useful, but interpretation depends on the sequence, timing, and analysis of the periods. Those details are not reported in the registry record. The available information therefore establishes the study question and broad design, but not how the primary clinical comparison was estimated.

3. Trial Design

The trial is identified as NCT02920970 and is titled “The Clinical Comparison of Narafilcon A and Stenfilcon A Contact Lenses.” It is listed as randomized, single-masked, and crossover, with completed status. The sponsor is CooperVision, Inc. The condition is myopia, and enrollment is listed as 72.

The record lists narafilcon A and stenfilcon A as device interventions. In each description, participants are randomized to wear a lens pair for one week during the crossover study. The brief description says the comparison concerns clinical performance and subjective acceptance when the lenses are used on a daily-wear, daily-disposable basis. The record does not describe the randomization sequence, the order in which each participant wore the lenses, or whether a washout period was used.

The study start is listed as 2016-09-01, and primary completion is listed as 2016-12-22. These dates describe the registry record’s timing; they do not establish when each participant completed each lens-wearing period. The masking field says single, but which people were masked is not reported in the registry record. No additional details about masking procedures are given.

In general, random allocation is intended to reduce systematic differences in how study conditions are assigned. In a crossover trial, the participant serves as a reference for comparisons across conditions, but the analysis must account for the paired or repeated nature of the observations. Period effects, order effects, and carryover are also relevant considerations in general. The registry record does not report how these features were addressed, so the design label alone cannot establish the analysis used or the validity of a particular estimate.

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: There were 72 participants were enrolled in the study, of which 70 were dispensed a contact lens to wear and 2 failed screening.

First Intervention

Reasons for not completing this period:

Second Intervention

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: There were 2 participants excluded from the analysis for narafilcon A due to protocol deviations

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 Ocular Physiology, measured over 1 week.

The stated primary endpoint is ocular physiology assessed by biomicroscopy. The registry description gives a scale from 0 to 4 in 0.25 steps, where 0 is normal and 4 is severe. The unit is described as units on a scale, and the summary parameter is the mean with standard deviation. The timeframe is one week.

In general, a clinical scale translates observations into ordered values so that findings can be described consistently. A mean can summarize the average recorded score, while a standard deviation describes how dispersed individual scores are around that mean. These summaries can help readers understand both the central level and the variability of measurements, although a mean does not show the full distribution or the pattern of individual observations.

Biomicroscopy is the method named for the ocular physiology assessment in the record. The registry does not provide further detail about the specific observations scored, the assessor procedures, or the interpretation of changes on the scale. It also does not report a single reduced comparison of the lens groups for this endpoint. The record notes that 2 participants were excluded from the narafilcon A analysis due to protocol deviations, but it does not state the corresponding analysis population or explain how the exclusion affected the endpoint estimate.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The study is listed as randomized, single-masked, and crossover. These labels describe broad design features but do not supply the analysis details. The registry record does not report the randomization procedure, masking roles, treatment sequence, period structure, or statistical model used for the primary outcome.

What does randomization contribute?

In general, randomization assigns study conditions using a chance-based process. Its purpose is to reduce systematic differences in assignment that could otherwise influence comparisons. Randomization does not guarantee that every characteristic will be balanced, and it does not by itself remove bias from missing data, deviations, or measurement. The record says the trial was randomized, but details of the procedure and allocation concealment are not reported in the registry record.

How does a crossover design affect analysis?

In general, a crossover design observes participants under more than one condition. Measurements from the same participant are usually correlated, because they share participant-specific characteristics. A within-participant analysis can account for this pairing and may be more precise than a comparison that ignores it. At the same time, interpretation can depend on treatment order, time period, and whether an earlier condition influences observations in a later period. The registry record does not report the sequence details, washout arrangements, or the model used to account for these features.

What does the endpoint summary represent?

The primary outcome is described as a mean on a biomicroscopy scale, with standard deviation as the measure of dispersion. In general, the mean summarizes the average of recorded values, and the standard deviation describes how spread out those values are. A scale score is not automatically a direct measure of a participant’s overall experience; it represents the observations defined by the assessment instrument. The registry record gives the scale anchors and increments but does not explain which specific ocular findings were scored or how the score was constructed.

When two means are compared, an estimated contrast and its uncertainty are usually needed to judge the direction and precision of the difference. The record does not include the means, standard deviations, or an estimated contrast for the primary outcome. Because the outcome is flagged as involving several categories or time points and is not reduced to one comparison, interpreting a single mean contrast would also require knowing which category or time point it represents. Those details are not reported in the registry record.

Why does over-dispersion matter in general?

Over-dispersion occurs when the observed variability is greater than a statistical model assumes. In general, a model that understates variability can produce uncertainty estimates that are too narrow and tests that are too optimistic. The primary endpoint is described with a mean and standard deviation, but the registry record does not report model diagnostics or indicate whether over-dispersion was considered. It is therefore not possible to say whether this issue arose or how it was handled in the trial analysis.

What do p-values and confidence intervals add?

In general, a confidence interval expresses uncertainty about an effect estimate under the assumptions of the analysis. A narrow interval indicates greater precision than a wide interval, though precision does not establish clinical importance. A p-value measures how compatible the observed data are with a specified null model; it does not give the probability that the null hypothesis is true. Neither statistic is reported for the primary comparison in the registry record, so no inferential conclusion can be reconstructed from the design description alone.

How should the planning description be read?

The record describes planning illustrations based on the observed effect, a two-sided significance level of 0.05, equal allocation, and a normal approximation. It also says the effect to detect is a stated fraction of the observed effect. No numerical planning results are included in the registry record for interpretation. In general, planning calculations estimate the sample size needed under chosen assumptions; they are not observed power and do not establish that a completed study had adequate precision. The registry record does not report the trial’s own sample-size justification, so the planning description cannot be treated as that justification.

The record lists 0 analyses. This means the registry entry does not include analysis records for the outcomes; it does not establish that no analysis was conducted outside the registry. The methods actually used for the primary endpoint, including any adjustment, handling of repeated measurements, or sensitivity analysis, are not reported in the registry record. Consequently, the outcome description supports an account of what was intended to be measured, but not a reconstruction of the statistical analysis.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists 11 outcome measures, while the primary outcome is flagged as involving several categories or time points and not being reduced to one comparison. It does not report how the primary comparison was selected from those categories or time points, whether multiple comparisons were planned, or whether any multiplicity adjustment was used. The number and structure of secondary comparisons are not described in the available record.

In general, when several hypotheses are tested, the chance of obtaining at least one apparently unusual result can increase if each test is interpreted separately. Multiplicity procedures can control that concern, but they involve choices about which outcomes or comparisons belong to the same testing family. Without the trial’s statistical analysis plan or analysis details, it is not possible to determine what approach, if any, was used.

The record states that 2 participants were excluded from the narafilcon A analysis due to protocol deviations. It does not report the reasons in detail, the number of participants with missing measurements for each outcome, or the handling of missing data. The analysis population definitions are not reported in the registry record. It is also unclear whether the excluded participants contributed observations for the other lens condition.

In general, missing-data methods rely on assumptions about why measurements are unavailable and how missingness relates to observed or unobserved outcomes. Excluding observations can change the population represented by an analysis, while imputation or model-based approaches require their own assumptions. Because the registry record does not describe a missing-data strategy or analysis populations, the influence of exclusions and missing observations cannot be assessed.

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.

Most frequent non-serious adverse event terms

The registry lists serious adverse events separately from other adverse events for each lens group. For stenfilcon A, 70 participants were at risk for serious events and 0 were affected; 70 were at risk for other events and 2 were affected. For narafilcon A, 70 were at risk for serious events and 0 were affected; 70 were at risk for other events and 6 were affected. Deaths are listed as 0 in both groups.

These are descriptive counts, not a statistical comparison. The record does not report the types or severity details of the other adverse events, and serious-event terms are not reported in the registry record. The listed counts do not establish whether each affected participant experienced one or multiple events, nor do they provide timing or duration. Those definitions and details are not reported in the registry record.

The study is a crossover trial, and the registry lists at-risk counts for each lens group. The record does not explain how exposure periods or adverse-event attribution were handled for these summaries. The counts should therefore be read as the registry’s group-specific figures rather than as a complete account of comparative safety. They do not answer the primary ocular physiology question or establish a causal difference between lenses.

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

The record establishes that a randomized, single-masked crossover study compared narafilcon A and stenfilcon A contact lenses, with ocular physiology listed as the primary outcome. It also documents a biomicroscopy scale, the one-week timeframe, and a protocol-deviation exclusion from the narafilcon A analysis. These details identify the intended comparison and some features relevant to interpretation.

The record does not report numerical primary outcome results or a single reduced comparison. It therefore cannot show the observed mean scores for the lenses, the size or direction of a contrast, or the precision of an estimate. It also does not report a p-value or confidence interval for the primary outcome. No conclusion about the magnitude, statistical significance, or clinical importance of a lens difference can be drawn from the registry information.

In general, a result’s meaning depends not only on an estimate but also on how the outcome was defined, who was analyzed, how repeated observations were handled, and what uncertainty surrounds the estimate. The registry record leaves important aspects of those methods unreported. In particular, the sequence and analysis details for the crossover design, the handling of missing observations, and the multiplicity approach are not described.

The safety counts provide descriptive information about serious and other affected participants, but the record does not report adverse-event terms for the serious-event category or details for the other events. These figures should not be treated as proof of equivalence or of a difference. They are also distinct from the primary efficacy endpoint and do not replace its missing numerical comparison.

The planning description concerns hypothetical calculations under stated assumptions, not observed study performance. Without numerical planning outputs or a reported trial-specific sample-size justification, it cannot establish the achieved precision of the completed study. Overall, the registry record describes the design and intended outcome but does not support a complete statistical interpretation of the primary comparison.

13. Why This Trial Matters Statistically

This trial is statistically notable because its crossover design makes the relationship between repeated observations central to interpretation. In general, comparisons within the same participant can account for stable participant characteristics, but the analysis must preserve the pairing. Sequence, period, and possible carryover effects may also matter. The registry record identifies the crossover design but does not report the details needed to evaluate how these features were handled.

The primary endpoint is a scored biomicroscopy assessment rather than a measurement with a naturally self-explanatory unit. The record provides scale anchors and step size, which help define how scores are recorded, but it does not report the underlying observations or a numerical comparison. That makes the distinction between knowing the endpoint’s measurement framework and knowing the study result especially important.

The record also flags that the primary outcome involves several categories or time points and was not reduced to one comparison. This highlights a common interpretive challenge: a study may collect multiple outcome components, while readers need a clearly defined primary contrast to assess the main question. The registry record does not describe how those components were selected or handled statistically.

Finally, the reported protocol-deviation exclusion and the absence of analysis details illustrate why an outcome label alone is not enough. Readers need to know which observations were analyzed and how missingness, repeated measurements, and multiple comparisons were addressed. Since those details are not reported in the registry record, the available material is most useful for understanding the study’s broad design and measurement plan, not for judging the estimated effect.

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 record does not report numerical results for the primary outcome, including group means, standard deviations, an estimated contrast, or a confidence interval. It also does not reduce the outcome’s several categories or time points to one comparison. This prevents assessment of the primary outcome’s direction, size, and precision.

Although the design is described as randomized, single-masked, and crossover, the record does not report the randomization sequence, the identity of the masked parties, the order of lens exposure, or any washout arrangements. It does not identify the statistical model or explain how repeated observations, period effects, or possible carryover were addressed. These omissions limit appraisal of whether the analysis appropriately reflected the design.

The record notes that 2 participants were excluded from the narafilcon A analysis due to protocol deviations but does not describe the deviations further. Analysis populations, missing-data counts, and missing-data methods are not reported in the registry record. It is therefore unclear how exclusions and unavailable measurements affected the reported analysis, which itself is not numerically available.

The record lists 11 outcome measures and 0 analyses, but does not describe the multiplicity strategy or identify a statistical analysis plan. It does not report the trial’s own sample-size justification. The description of planning illustrations does not include numerical outputs, and those calculations are not a substitute for observed results.

Safety information is limited to group-specific at-risk and affected counts. Serious-event terms and details about other adverse events are not reported in the registry record. These specific reporting gaps restrict both efficacy and safety interpretation.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: The Clinical Comparison of Narafilcon A and Stenfilcon A Contact Lenses — NCT02920970.
• Registry record last updated 2019-01-16; status last verified 2018-07.
• Results first posted 2019-01-16.
• 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

NCT02920970 is a completed, randomized, single-masked crossover study sponsored by CooperVision, Inc., comparing narafilcon A with stenfilcon A contact lenses in participants with myopia. Enrollment is listed as 72. The study start is 2016-09-01, and primary completion is 2016-12-22. Each lens is described as being worn as a pair for one week.

The primary outcome is ocular physiology assessed by biomicroscopy on a 0-to-4 scale in 0.25 steps, with 0 described as normal and 4 as severe. The registry record notes that 2 participants were excluded from the narafilcon A analysis due to protocol deviations. It lists 11 outcome measures and 0 analyses, and does not report a single reduced primary comparison or numerical primary results.

Safety entries list 0 serious-event affected participants in each group and other-event affected counts of 2 for stenfilcon A and 6 for narafilcon A. The record does not provide a detailed statistical analysis, missing-data approach, or multiplicity strategy.