This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record.
1. Trial at a Glance
GATSBY was a completed phase 1/2, single-group trial evaluating gevokizumab in participants with scleritis. The registry records 8 participants, 1 arm, no masking, and a treatment-focused primary purpose. Its registered primary endpoint assessed whether scleral inflammation improved by at least 2 grades or reached Grade 0 by the Week 16 visit.
| Feature | GATSBY |
|---|---|
| Phase | Phase 1/2 |
| Status | COMPLETED |
| Condition | Scleritis |
| Design model | SINGLE_GROUP |
| Allocation | NA |
| Masking | NONE |
| Primary purpose | TREATMENT |
| Enrollment | 8 |
| Number of arms | 1 |
| Intervention | Gevokizumab (device) |
| Lead sponsor | National Eye Institute (NEI) |
| Sponsor type | NIH |
| Start date | 2013-03 |
| Primary completion date | 2014-07 |
| Results posted | Yes |
| ClinicalTrials.gov | NCT01835132 |
2. Clinical Question
The registered clinical question can be framed as whether treatment with gevokizumab is associated with improvement in scleral inflammation in the study eye or eyes by the Week 16 visit among participants with scleritis.
Population
Participants with scleritis enrolled in the GATSBY study.
Intervention
Gevokizumab (device).
Comparator
There was no comparator arm. The trial used a single-group design.
Primary question
How many participants had at least a 2-step reduction or reduction to Grade 0 in scleral inflammation on or before the Week 16 visit?
3. Trial Design
Gevokizumab
- Intervention: Gevokizumab (device)
- 8 participants enrolled
- No separate comparator arm
- Primary assessment at the Week 16 visit
No control group
- The design is single-group
- Allocation is recorded as NA
- Masking is recorded as NONE
- Between-group treatment effects therefore cannot be estimated from this design
4. Endpoints
| Endpoint | Registry definition | Time frame |
|---|---|---|
| Primary endpoint | Number of Participants With at Least a 2-step Reduction or Reduction to Grade 0 in Scleral Inflammation in the Study Eye (or Eyes), According to the National Eye Institute (NEI) Photographic Scleritis Grading System, on or Before the Week 16 Visit. | Baseline and Week 16 |
NEI Photographic Scleritis Grading System
Scleral inflammation was graded following 10% Phenylephrine application using an ordinal scale ranging from Grade 0 through Grade 4+. The registered description defines Grade 0 as no scleral inflammation with complete blanching of vessels. Grade 0.5+ represents minimal or trace inflammation, Grade 1+ mild inflammation, Grade 2+ moderate inflammation, Grade 3+ severe inflammation, and Grade 4+ necrotizing inflammation.
| Grade | Registry description |
|---|---|
| 0 | No scleral inflammation with complete blanching of vessels. |
| 0.5+ | Minimal/trace inflammation with localized pink appearance of the sclera around minimally dilated deep episcleral vessels. |
| 1+ | Mild inflammation with diffuse pink appearance of the sclera around mildly dilated deep episcleral vessels. |
| 2+ | Moderate inflammation with purplish pink appearance of the sclera with tortuous and engorged deep episcleral vessels. |
| 3+ | Severe inflammation with diffuse significant redness of sclera; the details of superficial and deep episcleral vessels can't be observed. |
| 4+ | Necrotizing inflammation with diffuse redness of the sclera with scleral thinning and uveal show. |
The primary endpoint is therefore a responder definition built from an ordinal clinical grading system. A participant qualifies for the endpoint if the observed change satisfies either part of the registry definition: at least a 2-step reduction, or reduction to Grade 0, on or before Week 16.
5. Results
The ClinicalTrials.gov record indicates that results were posted, but no formal statistical analyses were posted to ClinicalTrials.gov. The registry reports enrollment and safety information, but it does not report a numerical outcome estimate for the registered primary endpoint.
What the registry reports
| Measure | Reported information |
|---|---|
| Enrollment | 8 participants |
| Primary endpoint result | No numerical outcome estimate reported in the registry record |
| Formal statistical analysis | No formal statistical analysis posted to ClinicalTrials.gov |
| Serious adverse events | Gevokizumab: 0/8 affected / at risk |
Typical analysis for the primary endpoint
For a single-group endpoint defined as the number of participants meeting a responder criterion, the most direct descriptive analysis would be the responder count and responder proportion among the evaluable participants. With a small sample such as 8 participants, an exact binomial confidence interval would generally be preferable to relying on a large-sample normal approximation.
The clinically meaningful quantity is the proportion of participants satisfying the prespecified response definition. An exact confidence interval can communicate the substantial sampling uncertainty that accompanies a small denominator.
Because the registry does not report the primary endpoint outcome, neither a responder proportion nor a confidence interval for that proportion is available from the registry record.
6. Safety Results
The registry reports serious adverse events by arm as 0 of 8 participants in the gevokizumab arm.
Serious adverse events
Gevokizumab: affected / at risk
| Safety measure | Gevokizumab |
|---|---|
| Serious adverse events | 0/8 |
This is a descriptive safety result rather than a comparative treatment effect because there was no comparator group. The observation of 0 affected participants also should not be interpreted as proof that the intervention has no risk. With only 8 participants, uncommon events may not appear even when they can occur in a larger treated population.
7. Statistical Methodology
Single-group estimation
The central statistical feature of GATSBY is its single-group structure. Every enrolled participant received the same study intervention, so the primary analysis is naturally framed around estimation of the observed response frequency rather than comparison of two randomized treatment groups.
The parameter p represents the underlying probability that a participant satisfies the registered responder definition under the population and treatment conditions represented by the study.
Responder analysis
The primary endpoint converts the ordinal inflammation measurement into a binary clinical response indicator. A participant either meets the specified threshold of improvement or does not. This makes a binomial framework a natural way to summarize the endpoint.
Exact binomial confidence intervals
When the sample size is small, the uncertainty around a response proportion can be large. Exact binomial intervals avoid the poor coverage that can arise from simple normal-approximation intervals when the denominator is small or when the observed proportion is near 0 or 1.
If X is the number of responders among n evaluated participants, the binomial model provides a direct probability model for the responder count.
Ordinal measurement versus binary endpoint
The underlying scleral inflammation scale contains multiple ordered grades, from 0 through 4+. The primary endpoint does not retain every distinction in that ordinal scale. Instead, it defines a clinically meaningful threshold and summarizes whether that threshold was achieved.
Baseline-to-Week-16 assessment
The registry specifies the time frame as Baseline and Week 16. Statistically, the response definition therefore depends on comparing the participant's inflammation grade over the specified assessment period and determining whether the prespecified reduction criterion is met on or before the Week 16 visit.
8. Statistical Methods Explained
Why is this a single-group analysis?
The registry identifies the design model as SINGLE_GROUP and records 1 arm. There is therefore no randomized control group against which the observed response rate can be contrasted.
Why is the primary endpoint binary if the inflammation scale is ordinal?
The underlying measurement is ordinal because its categories have an ordered clinical meaning. The registered primary endpoint then applies a response threshold: at least a 2-step reduction or reduction to Grade 0. That threshold turns the underlying assessment into a yes-or-no responder outcome.
What does a responder proportion tell us?
A responder proportion describes the fraction of evaluated participants who satisfy the predefined clinical response criterion. It does not by itself describe the magnitude of improvement for every participant, the durability of improvement beyond the specified assessment period, or how the result compares with another treatment.
Why use an exact binomial interval with a small sample?
With only 8 enrolled participants, large-sample approximations can be unreliable. Exact binomial methods directly account for the discrete nature of the responder count and are therefore well suited to small single-arm studies.
Why can't a treatment hazard ratio be calculated here?
A hazard ratio is a comparative time-to-event measure that normally contrasts event hazards between at least two groups. GATSBY has one study arm and its registered primary endpoint is a response count at a defined assessment period, so a hazard ratio is not the natural effect measure for the primary endpoint.
What does 0/8 serious adverse events mean?
It means that the registry reports 0 participants affected among 8 participants at risk for the gevokizumab arm. It is a descriptive observation within this small study and does not establish that serious adverse events cannot occur.
9. Interpreting the Primary Endpoint
The primary endpoint is designed to identify a clinically meaningful improvement in scleral inflammation rather than merely a small numerical change. By requiring at least a 2-step reduction or reduction to Grade 0, the endpoint establishes a threshold that distinguishes responders from nonresponders.
The endpoint does not measure average inflammation across the group, and it does not preserve every level of the underlying ordinal scale in the final responder classification. Two participants with different degrees of improvement can both be counted as responders once they cross the predefined threshold.
Only 8 participants were enrolled. In a sample this small, each individual participant represents a substantial fraction of the observed study population. Consequently, even a seemingly clear responder pattern would have considerable statistical uncertainty when generalized beyond the participants studied.
A confidence interval around the responder proportion would quantify uncertainty due to the small sample. It would not describe the range of responses experienced by individual participants; instead, it would characterize uncertainty around the estimated population response probability under the statistical model.
Because the study contains one treatment arm, the primary endpoint can describe response within the treated group but cannot isolate a between-treatment effect. Without a comparator, observed improvement can be described but cannot be separated statistically from changes that might have occurred in the absence of the intervention using this study alone.
10. What This Design Can and Cannot Establish
What it can estimate
The study can describe the frequency of participants meeting its predefined scleral inflammation response criterion and summarize safety observations within the enrolled group.
What it cannot compare
The single-group design does not provide a randomized comparison of gevokizumab against another intervention or control condition.
What the ordinal scale contributes
The NEI grading system supplies an ordered measure of scleral inflammation that provides the basis for the registered response definition.
Why replication matters
A small single-group study can provide an initial estimate that may inform subsequent research, while larger comparative studies can address questions of relative treatment effect.
11. Analysis Population and Missing Data
The registry identifies an enrollment of 8 participants and provides the primary endpoint time frame as Baseline and Week 16. It does not report a separate analysis-population definition, a missing-data strategy, or an imputation method for the registered primary endpoint.
For a responder endpoint, the handling of participants without a valid Week 16 assessment can materially affect the estimated response proportion. A prespecified analysis would therefore ordinarily define which participants belong in the denominator and how missing or unevaluable assessments are handled.
12. Limitations
- Small sample size: the study enrolled only 8 participants, limiting precision and the ability to characterize uncommon outcomes.
- No comparator: the SINGLE_GROUP design does not provide randomized evidence separating treatment-associated change from changes that might occur without the intervention.
- Ordinal endpoint summarized as response: the primary endpoint reduces a multidimensional ordered grading scale to a binary responder classification.
- Limited reported efficacy detail: the registry does not report a numerical result for the primary endpoint.
- No formal statistical analysis posted: the ClinicalTrials.gov record does not provide a formal statistical analysis for the primary endpoint.
- Missing-data information: the registry does not report a specific imputation or missing-assessment strategy for the primary endpoint.
- Generalizability: the enrollment of 8 participants limits how confidently findings can be generalized to a broader population with scleritis.
- Safety precision: 0 serious adverse events among 8 participants is reassuring as a descriptive observation but cannot reliably characterize uncommon safety events.
13. Why This Trial Matters Statistically
GATSBY is a useful teaching example because it illustrates a different statistical problem from the large randomized survival trials that dominate many clinical-trial analyses. Its central task is estimation of a clinically defined response in a very small single-group study.
| Concept | How it appears in GATSBY |
|---|---|
| Single-group design | 1 study arm with an enrollment of 8 participants. |
| Responder endpoint | Response is defined by at least a 2-step reduction or reduction to Grade 0. |
| Ordinal measurement | Scleral inflammation is graded from 0 through 4+ using the NEI Photographic Scleritis Grading System. |
| Binary classification | The primary endpoint converts the ordinal assessment into responder versus nonresponder status. |
| Exact inference | An exact binomial framework is appropriate for estimating a response proportion in a very small single-group study. |
| Absolute estimation | The primary estimand is naturally expressed as a response probability rather than a hazard ratio. |
| Uncertainty | A small denominator makes confidence intervals especially important when interpreting an observed response rate. |
| Safety description | Serious adverse events are reported as 0/8 for the gevokizumab arm. |
14. Trial Timeline
Study start
The registry records the GATSBY study start date as 2013-03.
Initial inflammation assessment
The registered primary endpoint uses the baseline scleral inflammation grade as part of the response assessment.
Primary endpoint assessment
The primary endpoint is assessed on or before the Week 16 visit.
Primary completion
The registry records the primary completion date as 2014-07.
15. Statistical Interpretation of the Safety Result
The reported serious-adverse-event result is 0/8 in the gevokizumab arm. This is an observed count, not a probability that serious adverse events have a true rate of zero in the broader population.
With only 8 participants, the study has limited ability to detect uncommon events. The appropriate interpretation is therefore descriptive: no serious adverse events were reported among the 8 participants at risk in the registry's arm-level result.
16. Primary Endpoint: A Deeper Statistical View
The endpoint is a thresholded change score
The underlying NEI grading system is ordered. A participant's baseline and follow-up grades can therefore be viewed as two positions on an ordinal scale. The registered endpoint then asks whether the change satisfies a specific threshold.
This expression describes the structure of the registered endpoint. The actual registry wording specifies the response criterion as at least a 2-step reduction or reduction to Grade 0 on or before Week 16.
This distinction matters because ordinal clinical measurements contain more information than a binary responder indicator. The responder endpoint is easy to communicate and clinically interpretable, but it intentionally compresses information. A full ordinal analysis could potentially distinguish smaller from larger improvements, whereas the registered endpoint focuses on crossing a prespecified response threshold.
Why the endpoint is not a continuous mean
The grades are ordinal categories rather than measurements for which equal numerical distances necessarily have a quantitative interpretation. Treating the categories as a conventional continuous variable and calculating a mean would impose assumptions that are not part of the registered endpoint definition.
Why baseline matters
The primary endpoint explicitly references reduction from the baseline state. This means the same Week 16 grade can have different responder implications depending on the participant's baseline grade. The statistical analysis therefore needs the paired baseline and follow-up assessments rather than the Week 16 grade alone.
17. Results Interpretation vs Statistical Interpretation
Reported result
The registry reports enrollment of 8 participants and serious adverse events of 0/8 for the gevokizumab arm. It does not report a numerical result for the primary scleral-inflammation response endpoint.
Statistical interpretation
The natural efficacy summary is a single-group responder proportion with uncertainty quantified using an appropriate binomial method. No between-group effect can be estimated from the study design.
18. Sources
- ClinicalTrials.gov: GATSBY — NCT01835132.
- PubMed: PubMed record associated with the GATSBY trial.
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19. Record Summary
GATSBY illustrates the statistical structure of a small, single-group clinical trial with an ordinal clinical measurement and a prespecified responder threshold. The study enrolled 8 participants and evaluated gevokizumab for scleritis, with the primary endpoint defined as at least a 2-step reduction or reduction to Grade 0 in scleral inflammation in the study eye or eyes on or before the Week 16 visit.
The key statistical issue is that this endpoint is an estimated response proportion, not a comparative treatment effect. In a study of this size, exact binomial inference is more appropriate than relying on large-sample approximations, and the confidence interval is essential for communicating uncertainty. The absence of a comparator also means that an observed response cannot, from this trial alone, be converted into a randomized estimate of treatment benefit.