Topical Antibiotics and Intravitreous Injections: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Topical Antibiotics and Intravitreous Injections (NCT00410891), a na phase 4 study. The primary outcome is Positive Culture.

2. Clinical Question

In plain terms, the study asks whether bacterial culture was positive after participants received topical gatifloxacin in the setting of intravitreous injections. A positive culture is a binary outcome for each participant: the culture is either classified as positive or it is not. Across a group, the outcome can be summarized as the percentage with a positive culture.

The record does not describe a control condition, such as no topical antibiotic or another treatment. As a result, the central question that can be read from the record concerns the observed culture outcome after treatment, not a comparative treatment effect. The study description does not establish how the culture result would differ without gatifloxacin.

The registry lists 129 participants as enrolled, but does not report how many contributed a culture result to the primary outcome. The precise analysis population and the number with evaluable cultures are not reported in the registry record. Accordingly, the clinical question is identifiable, while its numerical answer and precision cannot be determined from the posted results.

3. Trial Design

This is a Phase 4, single-group study sponsored by Stanford University. The registry record lists enrollment of 129 and identifies the intervention as topical gatifloxacin, described as topical antibiotic use 4 times per day. The study was marked completed. Its recorded start was 2008-07, and its primary completion was 2009-12.

The study model is single group, and allocation is listed as NA. Masking is listed as none. These design details indicate that the record does not describe randomized assignment, blinding, or a concurrent comparator arm. The registry explicitly cautions that this is not a randomized comparison and that arms are not a like-for-like control comparison. The record therefore supports describing a treated group and its recorded outcome, but not attributing a difference to treatment relative to a control group.

The brief description says the study evaluates the efficacy of topical preoperative antibiotics in patients undergoing intravitreous injections. The primary outcome is positive bacterial culture after administration of study treatment. Its stated timeframe is Study day 1, assessed following administration of study treatment. The record does not provide further detail about the precise timing of treatment relative to injection or culture collection, the culture procedures, or participant eligibility.

Enrollment is not itself evidence that all enrolled participants were included in the primary analysis. The number with outcome data, exclusions from analysis, and analysis population are not reported in the registry record. The record lists one outcome measure and no analysis records. It does not report the statistical plan, a sample-size justification, or whether any interim analysis was planned or conducted. Those omissions limit interpretation of how the outcome was analyzed and how its precision was assessed.

Separate from the actual single-group design, the posted planning illustrations use a hypothetical two-arm framework, equal allocation, a two-sided significance level of 0.05, and a normal approximation. They are described as planning illustrations based on a fraction of the observed effect, not as the study's design or observed power. Such illustrations should not be mistaken for evidence that participants were actually randomized or assigned equally between two groups.

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.

Population: patient undergoing IVT

6. Primary Endpoint

The registry lists the primary outcome as Positive Culture, measured over Study day 1, assessed following administration of study treatment.

The primary endpoint is the percentage of patients with a positive bacterial culture following administration of study treatment. The outcome is defined for an individual as positive or not positive; the group-level percentage describes how common a positive result was among the participants included in the analysis. The registry record places assessment on Study day 1, following administration of study treatment.

A culture outcome can provide a structured way to record whether bacteria were detected in the relevant sample. Expressing the result as a percentage makes the outcome interpretable at the group level. General: for a binary endpoint, the percentage is a measure of the frequency of the event in the population being analyzed. Its meaning depends on the outcome definition, the time of assessment, and which participants have usable measurements.

The registry description does not specify culture collection procedures, laboratory methods, criteria for a positive result, or whether culture assessment was blinded. Those details are not reported in the registry record. The analyzed denominator and observed percentage are also not reported, so the result's precision and the extent of missing outcome data cannot be assessed.

The endpoint is an outcome after treatment, not by itself a comparison of treatment strategies. Without a concurrent comparator, a positive-culture percentage cannot establish how the result would have differed under another approach. The posted results do not report the numerical endpoint value, so no conclusion about its observed frequency can be drawn from this record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The available information allows a limited explanation of the statistical concepts relevant to this study, but not a reconstruction of its analysis. The primary measure is described as a percentage of patients with a positive culture. The registry record does not state a statistical analysis method, a model, a test, an effect estimate, or an uncertainty interval. These details are not reported in the registry record.

What a binary percentage represents

General: a binary outcome has two possible categories for each person, such as positive or not positive. A group percentage expresses the share of people in the analysis population who experienced the event. For this study, the event is a positive bacterial culture following study treatment. To interpret such a percentage, the reader needs both the count of positive results and the number of participants whose results were assessed. Neither is reported for the primary endpoint.

The enrollment count of 129 does not establish the denominator for the culture result. Some participants could lack an assessable measurement, or the analysis population could be defined differently from enrollment; the record does not say whether this occurred. It does not report how missing culture observations were handled. Consequently, there is no basis to infer a positive-culture count, denominator, or percentage.

Estimation and uncertainty

General: an observed percentage is an estimate of the event frequency in the population represented by the analyzed participants. Its precision depends in part on the amount of outcome information and the event frequency. A confidence interval expresses uncertainty around an estimate under specified statistical assumptions. It is not a guarantee about the result and does not account automatically for bias from selection, measurement, or study design.

No primary-outcome percentage or confidence interval is reported in the registry record. Precision therefore cannot be assessed. If an interval were available, it would still need to be interpreted in light of the single-group design, outcome ascertainment, and analysis population. An interval around an outcome frequency would describe uncertainty in that frequency; it would not create a missing control comparison.

Hypothesis tests and p-values

General: a hypothesis test evaluates data against a specified null hypothesis using a statistical model and test procedure. A p-value describes how unusual data at least as incompatible with that null hypothesis would be under the model if the null were true. It is not the probability that a treatment is effective, nor does it measure the size or clinical importance of an effect.

The registry record reports no p-value, null hypothesis, or test for the primary outcome. In a single-group study, a test would need a defined reference value or some other explicit comparison to answer a statistical question. No such reference or test is reported. It would be inappropriate to infer one from the outcome name alone.

Over-dispersion and model choice

General: over-dispersion arises when observed variation is greater than a statistical model expects. It can affect uncertainty estimates and tests in settings where outcomes are modeled as counts or proportions, particularly when observations are more variable than the assumed model allows. Assessing it requires a specified model and relevant data. The registry record does not report a model or diagnostics, so it is not possible to say whether over-dispersion was relevant or assessed in this study.

The endpoint is described as a percentage, but that description alone does not identify the model used to estimate or test it. Analyses might differ in assumptions, handling of covariates, or treatment of missing results. None of those choices is reported. General statistical explanations therefore clarify possible concepts but should not be mistaken for the study's actual methods.

Planning illustrations are not trial analyses

The record describes planning illustrations computed from the observed effect, not from the trial's own design. Their stated assumptions include a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect to detect defined as a stated fraction of the observed effect. For non-time-to-event outcomes, the illustrations are expressed as participants per arm. The study itself is single-group, so the hypothetical equal-allocation framework is not its recorded design.

General: a sample-size calculation asks how much information a hypothetical study would need under specified assumptions. It is not a result observed in participants. A planning calculation based on an observed effect is particularly dependent on that effect estimate and on the assumptions used. The record's planning assumptions do not establish the trial's original sample-size rationale, which is not reported in the registry record.

These planning illustrations are not observed power. Observed power is not a substitute for examining an effect estimate and its uncertainty, and the registry record does not report an endpoint estimate or confidence interval. The illustrations should therefore be interpreted only as hypothetical planning exercises under their stated assumptions, not as evidence about the study's outcome or design.

Overall, the statistical concepts can explain what a binary outcome, uncertainty interval, hypothesis test, or planning calculation would mean in general. The actual analysis choices and numerical primary-outcome findings are not reported in the registry record.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Topical Antibiotic")
n      <- c(129)
events <- c(10)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Topical Antibiotic  129  10  7.8  3.8  13.8  4.3  13.7  4.3  13.7

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists one outcome measure, identified as Positive Culture. That does not establish that only one outcome was collected or considered during the study; it describes what is listed in this record. No analysis records are listed. The record does not report whether multiple hypotheses, endpoints, subgroups, or time points were tested, or whether any adjustment for multiple testing was used. Multiplicity procedures are not reported in the registry record.

General: when several statistical questions are tested, the chance of at least one apparently notable result can rise if each test is interpreted separately. Adjustments or a prespecified hierarchy can help address that issue, but the appropriate approach depends on the analysis plan. Since the record does not report the full analysis plan or testing procedures, it is not possible to assess multiplicity handling for this study.

The record lists enrollment of 129 but does not report the number of participants with an evaluable primary outcome. Missing culture data, withdrawals, exclusions, and reasons for missingness are not reported in the registry record. The approach to missing data—including whether any imputation or sensitivity analysis was used—is also not reported. It is therefore not possible to determine how missing outcome observations could affect the reported result.

The analysis population is not described. The record does not say whether the primary analysis included all enrolled participants, only participants who received treatment, or only those with a culture measurement. Those populations can differ, and their definitions matter when interpreting a percentage.

The record does not report a statistical analysis plan, interim analyses, or a sample-size justification. The planning illustrations described separately are hypothetical calculations and do not establish the study's original design rationale or analysis decisions. These omissions leave the handling of multiplicity, missing outcomes, and analysis populations uncertain.

12. 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 0% reporting threshold.

The adverse-event record lists a Topical Antibiotic group with 129 participants at risk for serious adverse events and 0 affected. It also lists 129 at risk for other adverse events and 0 affected. These are the figures recorded for the group; they should be read as reported counts, not as proof that no adverse events of any kind occurred beyond what the record captures.

Deaths are listed as null rather than as a numeric count. A null entry is not the same as a reported zero. The number of deaths is not reported in the registry record. No serious adverse-event terms are listed.

General: a count of affected participants is interpretable in relation to the population at risk and the way events were defined and collected. The record does not provide further detail about event definitions, follow-up duration for safety, ascertainment procedures, or missing safety data. It also does not report comparative safety data from a control group. The reported counts therefore describe the registry's entries for this treated group, not a comparison between treatment strategies.

These safety entries do not resolve the missing primary outcome result. They concern adverse-event reporting, whereas the primary endpoint is positive bacterial culture. The registry record does not report the numerical primary endpoint or a statistical analysis relating culture results to safety outcomes.

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

The record establishes that a completed Phase 4, single-group study evaluated topical gatifloxacin in patients undergoing intravitreous injections. It identifies positive bacterial culture following study treatment as the primary outcome and gives Study day 1 as the assessment timeframe. It also records enrollment of 129 participants and describes topical use 4 times per day.

What the record does not establish is the observed frequency of positive cultures. No count, percentage, confidence interval, or p-value for that outcome is reported. The record also does not provide the number of participants whose culture results were analyzed. It is therefore not possible to quantify the observed outcome or its precision from the posted results.

The study design places a further limit on interpretation. It is single-group, with no comparator described, allocation listed as NA, and masking listed as none. An outcome measured after treatment can describe what was observed in the treated group, but without a concurrent control group it does not show how outcomes would have differed under another treatment condition. The record explicitly warns against treating arms as a like-for-like control comparison.

General: an association between an intervention and an outcome in a single group does not by itself establish that the intervention caused the outcome. Other factors, the natural course of events, measurement procedures, and participant selection may influence the observations. A randomized comparative design can address some causal questions more directly, but the registry record does not describe such a design.

The safety record lists 0 participants affected by serious adverse events and 0 affected by other adverse events among 129 at risk in each category; deaths are not reported as a numeric value. These entries should be interpreted as registry reporting, not as a complete account of all possible outcomes or as comparative safety evidence.

The most defensible conclusion is about the record's scope: it specifies the question and design, but does not report the primary numerical result or its analysis. It neither supports a numerical claim about positive cultures nor establishes a comparative treatment effect. The missing result should not be mistaken for a favorable or unfavorable finding.

14. Why This Trial Matters Statistically

This study is statistically instructive because it separates a clearly stated endpoint from the information needed to interpret that endpoint. Positive bacterial culture is defined as the primary outcome, and its assessment timing is identified. Yet the registry record does not give the outcome frequency, analysis denominator, or uncertainty estimate. A defined endpoint alone is not enough to judge the size or precision of a finding.

The design also matters to the kind of inference available. A single-group study can record an outcome in participants who received an intervention. Without a comparator, it cannot directly estimate a difference between treatment conditions. The record's warning that this is not a randomized comparison reinforces why observed outcomes should not be converted into comparative or causal claims.

The enrollment count illustrates another basic statistical distinction: enrollment and analysis sample size are not necessarily the same. The registry lists 129 participants, but does not say how many had assessable primary outcomes. Without the denominator and missing-data information, even a reported percentage would require context to judge its completeness and representativeness.

The planning illustrations offer a separate lesson. They use hypothetical assumptions that include equal allocation between two arms, although the recorded study is single-group. Planning calculations are conditional on their assumptions; they do not describe the actual design, observed power, or the study's original sample-size justification. Keeping planning scenarios separate from trial findings prevents a hypothetical design calculation from being mistaken for evidence.

Finally, the safety counts and primary endpoint address different questions. Counts of adverse events do not supply the missing culture result, and the absence of a reported comparison limits safety interpretation as well. Together, these features show why statistical reading depends not only on an endpoint label but also on outcome data, analysis population, uncertainty, and design.

15. 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 central limitation for interpreting the primary outcome is that its numerical result is not reported in the registry record. The record gives the endpoint definition and timeframe but no positive-culture count, percentage, confidence interval, or test result. The number of participants contributing to that outcome is also not reported, despite an enrollment count of 129.

The single-group design limits comparative interpretation. No concurrent control group is described, allocation is listed as NA, and masking is listed as none. The record does not support a direct estimate of how the outcome would differ under another treatment condition. The registry itself cautions that the study is not a randomized comparison.

Important operational details are also absent. Eligibility criteria, culture collection and laboratory procedures, the criteria for a positive culture, and the exact relationship between treatment and assessment are not reported in the registry record. These details can affect how an outcome is measured and which population the results represent.

The record does not report the analysis population, exclusions, missing outcome data, or methods for handling missingness. It also does not report the statistical analysis plan, inferential methods, multiplicity handling, interim analyses, or sample-size justification. Without these details, the analysis cannot be independently understood from the registry record.

Safety interpretation has related limits: the record lists zero affected for serious and other adverse events, but does not give further information about event ascertainment or safety follow-up. Deaths are not reported as a number. No comparative safety group is described. These limitations do not imply that unreported events occurred; they define what cannot be determined from the record.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Topical Antibiotics and Intravitreous Injections — NCT00410891.
• Registry record last updated 2017-11-06; status last verified 2017-10.
• Results first posted 2014-06-12.
• 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.

19. Record Summary

The registry record describes NCT00410891, “Topical Antibiotics and Intravitreous Injections,” as a completed Phase 4, single-group study sponsored by Stanford University. It lists enrollment of 129, a recorded start of 2008-07, and primary completion of 2009-12.

The intervention was topical gatifloxacin, described as topical antibiotic use 4 times per day. The primary outcome was the percentage of patients with a positive bacterial culture following study treatment, assessed on Study day 1. The record lists one outcome measure and no analysis records, but does not report the primary outcome result or its analysis population.

Allocation is listed as NA and masking as none; no comparator is described. The record cautions that this is not a randomized comparison. For safety, 0 of 129 at risk were listed as affected by serious adverse events and 0 of 129 by other adverse events; deaths are not reported as a numeric count. The record does not report the statistical plan, missing-data handling, or sample-size justification.