Subjective Evaluation of a Commercially Marketed Contact Lens Amongst a Subset of the Contact Lens Wearing Population: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Subjective Evaluation of a Commercially Marketed Contact Lens Amongst a Subset of the Contact Lens Wearing Population (NCT01007916), a randomized na study. The primary outcome is Comfort Upon Insertion.

2. Clinical Question

3. Trial Design

The registry describes a randomized, single-masked crossover study comparing Lotrafilcon B contact lenses with participants’ habitual contact lenses. The enrollment was 50, the study status is completed, and the listed phase is NA. The record identifies CIBA VISION as the sponsor and gives a start of 2009-10 and primary completion of 2010-01.

In a crossover design, participants receive each of the compared conditions in sequence. The registry lists two sequences: Lotrafilcon B followed by habitual lenses, and habitual lenses followed by Lotrafilcon B. This structure can allow a participant’s experience under one condition to be considered alongside their experience under the other. The registry does not report the sequence allocation details, the timing or duration of each period beyond the primary outcome’s four weeks of wear, or any washout procedures.

The study is listed as single-masked, but which people were masked and how masking was maintained are not reported in the registry record. Both lens products were worn bilaterally at a frequency and in a modality typical for habitual lenses, as prescribed by the participant’s regular eye care practitioner; extended wear was described as not exceeding 6 nights.

The primary outcome analysis was per protocol, with exclusions for major protocol deviations determined by masked review. The registry does not report the specific deviations or the detailed analysis model. The primary outcome is continuous and summarized by means and standard deviations. The record lists one outcome measure and no posted secondary outcomes. It lists no analyses 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: One participant was enrolled but not dispensed due to failing inclusion/exclusion criteria. This participant is included in the Actual Enrollment calculation, but not Participant Flow or Baseline Characteristics calculations.

Period 1, 4 Weeks of Wear

Reasons for not completing this period:

Period 2, 4 Weeks of Wear

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Analysis conducted per protocol, with exclusions due to major protocol deviations as determined by masked review.

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Comfort Upon Insertion, measured over 4 weeks of wear.

The primary endpoint was comfort upon insertion, assessed after four weeks of wear. Participants recorded a single retrospective evaluation on a 10-point questionnaire scale, with 1 indicating poor comfort and 10 indicating excellent comfort. The endpoint therefore captures participants’ own assessment of insertion comfort over the stated wear period; it is not an objective clinical measurement.

A continuous rating can be summarized by a mean, which represents the average recorded score, and a standard deviation, which describes how dispersed scores were around that average. The registry reports a Lotrafilcon B mean of 8.7 with a standard deviation of 2.0 and a habitual-lens mean of 9.2 with a standard deviation of 0.9. These summaries describe the analyzed groups’ recorded scores, but do not show the distribution of individual responses or how scores changed over time.

A participant-reported comfort endpoint is relevant to a study asking about subjective lens experience. It also has limits: ratings can vary between participants, and a retrospective single assessment may not capture every experience during wear. The registry does not report questionnaire validation, details of how the retrospective rating was elicited, or whether participants completed repeated ratings during the four-week period.

7. Results Posted in the Registry

• Habitual: mean 9.20 versus 8.70 on control; difference 0.50 (95% CI -0.13 to 1.13), standardized effect d = 0.32; z-test p = 0.119.

8. Statistical Interpretation

9. Statistical Methods Explained

What does a mean describe?

For a continuous outcome such as a questionnaire score, the mean is the arithmetic average of the observed ratings in the analysis group. It offers a compact description of the group’s central score, but it does not show every participant’s response. The reported means were 8.7 for Lotrafilcon B and 9.2 for habitual lenses. Since the outcome scale runs from 1, poor, to 10, excellent, higher scores correspond to better-rated comfort on this questionnaire.

What does the standard deviation describe?

The standard deviation describes the spread of observations around a group mean. The posted standard deviations were 2.0 for Lotrafilcon B and 0.9 for habitual lenses. A larger standard deviation indicates more dispersion in recorded scores; it does not mean that every participant’s score differed by that amount, and it is not a confidence interval for the mean. The registry does not provide score distributions or individual observations.

How is the mean difference oriented?

The reported comparison is habitual minus Lotrafilcon B. Its estimate of 0.5 is consistent with the posted means, with the habitual-lens mean higher. Keeping the comparison’s direction explicit is important: reversing the subtraction would reverse the sign, even though the underlying group means would not change. The estimate describes the observed difference in means, not a percentage change or a probability that one lens condition is better.

What does the confidence interval add?

A confidence interval expresses uncertainty around an estimate under the statistical procedure used to construct it. The reported interval extends from -0.128 to 1.128. Its inclusion of zero means that a zero difference is among the values compatible with this interval. The interval also allows values on either side of zero, so the direction of the underlying difference is not determined precisely by this comparison. The registry does not state the interval construction method or identify a crossover-specific model.

What does the p-value mean?

The unadjusted p-value was 0.119. In general, a p-value describes how compatible data are with a specified null hypothesis under the assumptions of a statistical test; it is not the probability that the null hypothesis is true, nor a measure of the size or practical importance of an effect. Because the registry does not report the test specification or full analysis plan, the p-value should be interpreted with that limitation in mind. It is labeled unadjusted, and the record does not describe adjustments for multiple testing.

Why does the crossover structure matter?

In general, crossover studies can make use of within-participant comparisons because the same participant experiences both conditions. This can help account for stable differences between people. It also makes the analysis sensitive to the relationship between a participant’s ratings under each condition and to possible sequence or period effects. The registry lists randomized sequences but does not report how the comparison accounted for paired responses, sequence, period, or carryover. No particular analysis method should be assumed from the design label alone.

What is the role of the analysis population?

The primary outcome analysis is described as per protocol, with participants excluded for major protocol deviations as determined by masked review. Such an analysis describes outcomes among those retained under the stated protocol criteria, rather than necessarily including every enrolled participant. The registry does not give the deviation criteria or explain how missing endpoint scores were handled. The outcome arm counts are 47 for Lotrafilcon B and 46 for habitual lenses; these counts should not be treated as a complete account of enrollment or of all participants’ data.

These statistical summaries describe the posted observations and comparison. They cannot resolve the unreported details of model specification, missing-data handling, or crossover analysis. Those details would be needed to fully assess whether the statistical approach matched the design and analysis population.

10. Confidence Intervals and Precision

The reported mean difference is 0.5, with a confidence interval from -0.128 to 1.128. This interval communicates uncertainty in the estimated difference rather than the range of individual participant scores. The interval crosses zero, leaving the direction of the difference uncertain: values consistent with the interval include a small difference favoring Lotrafilcon B, no difference, and a difference favoring habitual lenses under the stated comparison orientation.

The endpoints are separated enough that the estimate is not highly precise about the size or direction of the contrast. The interval does not establish that the conditions are equivalent, nor does it show that any possible difference would be important to participants. A conclusion about equivalence would require an appropriate prespecified margin and analysis, neither of which is reported in the registry record.

The posted standard deviations, 2.0 for Lotrafilcon B and 0.9 for habitual lenses, also show that observed scores varied, particularly in the Lotrafilcon B group. These group-level summaries do not reveal how the paired scores varied within participants. Because the study is a crossover, the within-participant association can affect the precision of a paired comparison. The registry does not report that association or the method used to incorporate it.

The unadjusted p-value of 0.119 is another summary of uncertainty under a test, but it does not replace the interval or clarify the range of plausible effect sizes. The statistical test and interval method are not reported. Taken together, the estimate and interval warrant a cautious descriptive interpretation rather than a precise claim about the difference between lens conditions.

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 sample-size figures are planning illustrations, not observed enrollment results or observed power. They express participants per arm for 80% power and participants per arm for 90% power under the stated planning assumptions. The registry’s planning illustration uses a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is defined as the stated fraction of the observed effect.

For planning for 100% of the observed effect, the illustration gives 153 participants per arm for 80% power and 204 participants per arm for 90% power. For planning for 75% of the observed effect, it gives 271 participants per arm for 80% power and 363 participants per arm for 90% power. For planning for 50% of the observed effect, it gives 609 participants per arm for 80% power and 815 participants per arm for 90% power.

In general, power is the chance that a specified analysis would detect an effect of a chosen size if that effect were present, given the planning assumptions. The 80% and 90% columns represent different target chances of detection under those assumptions; targeting the higher power generally requires more participants. The illustrations also show that smaller effects need more participants to detect, because the groups’ outcomes are expected to be harder to distinguish when the target effect is smaller.

These figures are based on the observed effect and should not be read as the trial’s original design calculation. The registry does not report the trial’s own sample-size assumptions or justification. The figures are not a retrospective measure of the probability that this completed study detected an effect.

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 = 0.500; pooled standard deviation σ = 1.556.
2. n = 2 × (1.96 + 0.842)² × 1.556² / 0.500² = 152.1, rounded up to 153 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 <- 0.5                      # observed difference in means
sigma <- 1.55644706704965                     # 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(1007916)
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 = 153 (80% power), 204 (90% power)
 75% of observed effect: n per arm = 271 (80% power), 363 (90% power)
 50% of observed effect: n per arm = 609 (80% power), 815 (90% power)
power.t.test: 153.1 
Simulated power at n = 153 per arm: 0.800 (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 lists one outcome measure, Comfort Upon Insertion, and no posted secondary outcomes. It lists no analyses in the registry record. The comparison reports an unadjusted p-value of 0.119, but the record does not state whether other outcomes, time points, subgroup analyses, or interim comparisons were planned or conducted. A multiplicity adjustment or strategy is not reported. With no further analysis plan available in the record, it is not possible to determine how the reported comparison fits into any broader set of statistical tests.

The primary outcome population is described as per protocol, with exclusions for major protocol deviations determined by masked review. The record does not define those deviations, give the review criteria, or report how many participants were excluded from the primary analysis. It also does not explain whether the analysis population was defined before outcome data were reviewed.

Missing-data handling is not reported in the registry record. The available outcome summaries list 47 participants for Lotrafilcon B and 46 for habitual lenses, but the record does not explain whether all unavailable ratings were missing, whether any scores were imputed, or how incomplete crossover participation was treated. It also does not provide a participant flow description for the outcome analysis.

The design is randomized and crossover, but the statistical plan is not reported. The registry does not say whether the primary comparison used a paired model, accounted for period or sequence, or assessed carryover. The masking label is single, but who was masked is not reported. The record also does not describe any interim analyses, and none should be assumed.

These omissions limit assessment of the analysis’s alignment with the design and of possible bias from exclusions or missing scores. They do not change the posted descriptive values, but they constrain how confidently those values can be interpreted as an estimate of the intended crossover comparison.

14. Safety Results

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

Other (non-serious) adverse events

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

The registry’s safety entries list 0 serious adverse events affecting participants in the Lotrafilcon B group, among 49 at risk, and 0 in the habitual-lens group, among 48 at risk. It also lists 0 other adverse events affecting participants in each group, with the same respective at-risk counts. No serious adverse-event terms are listed. Death counts are not reported in the registry record.

These entries describe what was recorded for the listed groups and categories; they do not establish that no events of any kind occurred. The at-risk counts differ from the outcome-analysis counts, and the registry does not explain the relationship between those populations. It also does not provide event definitions, event timing, severity detail for other adverse events, or a fuller account of safety collection and follow-up.

Accordingly, the safety figures should be read narrowly as registry-reported counts of participants affected in the specified categories, not as a comprehensive safety assessment or a basis for comparing risks.

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

The registry reports participants’ retrospective comfort ratings after four weeks of wear. The mean score was 8.7 with Lotrafilcon B and 9.2 with habitual lenses. The mean difference, habitual minus Lotrafilcon B, was 0.5. The confidence interval ranges from -0.128 to 1.128, and the unadjusted p-value is 0.119. These statistics describe the posted comparison and its uncertainty.

The interval includes zero and values on both sides of zero. Therefore, the estimate does not precisely settle which condition had the higher underlying mean rating. It also does not demonstrate that the conditions are equivalent. The record does not state an equivalence margin or a non-inferiority objective.

The endpoint was subjective and retrospective, and the analysis was per protocol. The registry does not report full questionnaire details, the analysis model, missing-data procedures, or how the crossover pairing was handled. These limitations matter when considering what the estimated contrast represents. The result should not be extended beyond the specific comfort rating, analyzed population, and wear period described in the record.

Nor do these comfort data establish broader product performance or outcomes beyond the measure reported. The record lists no posted secondary outcomes. The safety entries report zero affected participants in the serious and other adverse-event categories for each listed group, but provide limited detail and do not report death counts.

In general, a trial result is one piece of evidence about a defined question; it is not a universal statement about every contact lens wearer or every pattern of lens use. Here, the registry supports a measured description of group ratings and the uncertainty around their reported difference. It does not support a definitive claim that one lens condition is superior, equivalent, or preferable for individuals.

16. Why This Trial Matters Statistically

This study is statistically notable for combining a subjective continuous outcome with a randomized crossover design. A crossover can allow comparisons within participants, but proper interpretation depends on how the analysis handles paired measurements and potential sequence or period effects. The registry gives the design and randomized sequences but does not describe the statistical model, making that distinction central to evaluating the comparison.

The endpoint is a participant rating on a bounded 10-point scale. The mean and standard deviation provide useful summaries, but they do not show the rating distribution, whether scores clustered near the high end, or how participants’ paired ratings related to one another. The different reported standard deviations—2.0 for Lotrafilcon B and 0.9 for habitual lenses—also make it important not to treat the group averages as a complete account of the response patterns.

The per-protocol analysis adds another interpretive consideration. Excluding participants for major protocol deviations may describe a selected analysis population, while the criteria and missing-data handling are not reported. The primary outcome counts differ by condition, but the record does not explain the flow of participants or reasons for unavailable scores.

Finally, the confidence interval covers values on both sides of zero. Its range and the unadjusted p-value of 0.119 call for attention to uncertainty rather than a simple ranking based on the means. The sample-size illustration is explicitly based on the observed effect, not the trial’s original design assumptions. Together, these details show why design, analysis population, and precision matter alongside the headline mean scores.

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 leaves several trial-specific details unreported. It does not describe the criteria used to select the contact lens-wearing population, beyond identifying myopia as a condition. The identity of those masked in this single-masked study and the procedures used to maintain masking are also not reported.

The crossover sequence descriptions establish which lens was worn first and second, but the timing and duration of each period, washout procedures, and handling of possible carryover are not reported. The outcome timeframe is four weeks of wear, but the record does not clarify how that timeframe maps onto each condition or sequence.

The primary endpoint is a participant’s single retrospective comfort rating. The registry does not report questionnaire validation, how the rating was administered, or whether ratings were collected at other points. The analysis population is per protocol, but the specific major deviations, participant flow, and missing-data procedures are not reported.

The record does not provide a detailed statistical analysis plan, including the model for the crossover data, the confidence interval method, or whether sequence and period were addressed. It lists no analyses and no posted secondary outcomes. The trial’s original sample-size assumptions and justification are not reported; the available planning illustration is based on the observed effect.

The safety information is limited to participant counts in adverse-event categories, with no event terms listed for serious events and no death counts reported. These gaps limit the ability to assess the full analysis process and safety experience from the registry record alone.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Subjective Evaluation of a Commercially Marketed Contact Lens Amongst a Subset of the Contact Lens Wearing Population — NCT01007916.
• Registry record last updated 2012-07-10; status last verified 2012-01.
• Results first posted 2011-02-25.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

21. Record Summary

The completed study was a randomized, single-masked crossover comparison of Lotrafilcon B contact lenses and participants’ habitual lenses in a selected contact lens-wearing population with myopia. Enrollment was 50. The primary endpoint was participant-rated comfort upon insertion after four weeks of wear, using a scale from 1, poor, to 10, excellent.

The per-protocol outcome summaries report means of 8.7 for Lotrafilcon B and 9.2 for habitual lenses. The reported mean difference was 0.5 for habitual minus Lotrafilcon B, with a confidence interval from -0.128 to 1.128 and an unadjusted p-value of 0.119. The interval includes zero, and important details of the crossover analysis and missing-data handling are not reported in the registry record.

Safety entries list zero participants affected in the serious and other adverse-event categories for each group. Death counts are not reported. The record lists no posted secondary outcomes and no analyses.