A Study to Evaluate the Safety and Efficacy of Abatacept in Patients With Diffuse Systemic Sclerosis (Scleroderma): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Study to Evaluate the Safety and Efficacy of Abatacept in Patients With Diffuse Systemic Sclerosis (Scleroderma) (NCT00442611), a randomized phase 1, phase 2 study. The primary outcome is Change in Modified Rodnan Skin Score.

2. Clinical Question

3. Trial Design

The registry record describes a randomized, triple-masked, parallel-group pilot study of abatacept and IV fluid placebo in people with systemic sclerosis. It lists Phase 1 and Phase 2 and an enrollment of 10. Stanford University is named as the sponsor. The recorded study start is 2008-11, primary completion is 2011-06, and status is completed.

Participants were assigned to an abatacept arm or an IV fluid arm. Abatacept was dosed based on weight and given intravenously. Both treatment descriptions specify administration on days 1, 15, 30 and monthly thereafter for a total of 7 doses. The comparator was described as placebo to match abatacept. The record labels the study triple-masked, but which groups of people were masked is not reported in the registry record. The specific randomization procedure and allocation-concealment details are also not reported in the registry record.

The trial's stated focus was safety and efficacy in diffuse systemic sclerosis, with the primary outcome defined as change in Modified Rodnan Skin Score at 6 months. The registry record also lists five secondary outcomes, covering oral aperture, hand extension, digital ulcerations, pulmonary function tests, and the Scleroderma Health Assessment Questionnaire. These additional measures give context to the study's scope, but their outcome values and analyses are not included in the posted results.

The design is a small pilot comparison. Its arm-level summaries can describe the recorded outcomes, but the registry record does not provide a reported inferential comparison for the primary continuous endpoint. The record also does not report a protocol-level sample-size justification, a detailed statistical analysis plan, or the specific analysis population.

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.

6. Primary Endpoint

The registry lists the primary outcome as Change in Modified Rodnan Skin Score, measured over 6 months.

The primary endpoint is change in Modified Rodnan Skin Score, abbreviated MRSS, at 6 months. MRSS measures skin thickness by rating 17 surface anatomic areas on a 0-3 scale. The scale anchors are 0 for normal skin, 1 for mild thickness, 2 for moderate thickness, and 3 for severe thickness with inability to pinch the skin into a fold. The total score ranges from 0 to 51, with 0 described as the best possible outcome and 51 as the worst possible outcome.

A change score expresses how the measure differs from its baseline value over the stated follow-up period. The registry record reports arm-level mean changes and standard deviations. A negative mean change indicates a decrease in the score over that period, while the standard deviation describes how dispersed individual changes were around the arm mean. The summary does not show the individual values or their distribution.

MRSS is used as a measure of skin involvement in systemic sclerosis, allowing skin thickness to be represented on a consistent score scale. The endpoint's relevance follows from the study's stated interest in skin thickening and fibrosis. It captures the skin-score outcome, not every feature of systemic sclerosis or every potential benefit or harm. The registry record does not report a threshold for a clinically meaningful change, so the clinical importance of a particular change cannot be determined from the posted score summaries alone.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous: each participant has a numerical MRSS change score, and the registry record summarizes those scores by the mean and standard deviation in each arm. The posted mean is the arithmetic average of the recorded changes in that arm. The standard deviation describes how far individual changes tend to lie from the arm mean. It reflects variability among observations, not the uncertainty in the mean itself. A confidence interval for a mean or a contrast would address estimation uncertainty, but no confidence interval is reported in the registry record.

For a randomized comparison, the central inferential question is generally the difference in outcomes between the assigned arms, interpreted with its uncertainty. A formal analysis can account for the observed variability and the amount of outcome information available. However, the registry record does not post an estimable two-arm comparison for this continuous outcome. It states that values are missing or not estimable for such a comparison. No test result, interval estimate, adjustment method, or model specification for the primary contrast is reported. Accordingly, the posted arm means should be read descriptively rather than as a complete comparative analysis.

In general, a confidence interval gives a range of values compatible with the data under a specified statistical procedure. Its width reflects precision: wider intervals indicate less precise estimates. An interval for each arm mean would not be a substitute for an interval for the between-arm contrast. The registry record reports neither kind of interval for the primary result, so the precision of the apparent arm separation cannot be evaluated from the posted summary statistics alone.

In general, standard deviations matter because greater spread makes a mean less precisely estimated when the amount of available information is limited. Strong skew, outliers, or other departures from assumptions may also affect how well a simple normal-based analysis describes a continuous outcome. The registry record gives arm-level standard deviations but does not provide individual data, distributional diagnostics, or an analysis method. It is therefore not possible to assess whether a particular model's assumptions were checked or whether an alternative method was considered.

Random allocation is intended to support fair comparisons by reducing systematic differences in treatment assignment. The record labels the study randomized, but details of sequence generation, allocation concealment, and implementation are not reported in the registry record. It is also labeled triple-masked. Masking can limit the influence of treatment knowledge on care, outcome assessment, or reporting, but the record does not identify which people were masked or describe whether masking was maintained.

The registry record lists planning assumptions for an illustrative sample-size calculation: a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation. It describes the effect to detect as a stated fraction of the observed effect. These are planning assumptions, not a report of the trial's original design calculation, and the record does not report a protocol sample-size justification. No numerical planning results are included in the registry record described for this analysis. Any such illustration is prospective planning information, not observed power or evidence about the result.

In general, a sample-size calculation depends on the effect a future study aims to detect, the variability of the outcome, the chosen significance level, and the desired probability of detecting that effect if it is present. Changing the target effect changes the planning requirement. Planning for a fraction of an observed effect explores a different target from planning to reproduce the full observed effect. In a pilot study, an observed effect estimate can be unstable, so planning values based on it should be treated cautiously. The registry record does not report enough detail to evaluate its own original recruitment target or design rationale.

Over-dispersion is a concept most often applied when observed count data vary more than a chosen statistical model expects. It can lead a model to understate uncertainty if ignored. The primary outcome in this study is a continuous score change, not a count outcome, and the registry record does not report an over-dispersion analysis. More generally, model choice should reflect the outcome's scale and observed distribution; the record does not provide the details needed to assess that choice.

Finally, statistical significance and clinical importance are different questions. A statistical test assesses compatibility with a specified null hypothesis under its assumptions. Clinical importance asks whether the size of a change matters in the context of the condition and measurement. No formal test or clinical-importance threshold is reported for the primary endpoint. The record's arm summaries therefore support a description of observed changes, but they do not provide a complete basis for either inferential or clinical conclusions.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Abatacept", "IV Fluid")
n   <- c(7, 3)
m   <- c(-8.6, -2.3)
sp  <- c(7.5, 15)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Abatacept  7  -8.600  7.500  -15.536  -1.664
CARM  IV Fluid  3  -2.300  15.000  -39.562  34.962

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists five secondary outcomes in addition to the primary MRSS change outcome. Because evaluating several outcomes can increase the chance of at least one apparently notable result when many tests are conducted, a statistical plan may specify how multiplicity is handled. No multiplicity procedure, testing hierarchy, or adjustment strategy is reported in the registry record. The record lists no analysis entries for these outcomes, so it does not establish which comparisons were conducted or how their results should be interpreted together.

Missing-data handling is also not reported in the registry record. There is no description of whether participants with unavailable follow-up scores were excluded, imputed, or handled using another method. The primary outcome population field contains no description. Although arm-level sample sizes are posted with the outcome summaries, the record does not explain how those numbers relate to enrollment, randomization, missing measurements, or the analysis population. It is not possible to determine from the registry record whether the reported summaries use an intention-to-treat population, a per-protocol population, or another defined group.

These omissions limit interpretation. Missingness can affect a comparison if availability of outcome measurements is related to treatment assignment or to the outcome itself. Multiplicity can affect the interpretation of findings across several outcomes. Without a stated analysis plan, missing-data method, and defined population, readers cannot assess whether those issues were anticipated or how they may have influenced the reported results. The registry record does not report interim analyses or other analysis-planning details.

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.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: infection (14.3%).

The registry record lists serious adverse events for the abatacept arm as affecting 1 participant among 7 at risk, and for the IV fluid arm as affecting 0 participants among 3 at risk. These are counts within the posted safety groups. They should not be confused with the primary MRSS outcome counts or interpreted as a comparative safety test. No confidence interval or formal statistical comparison of serious adverse events is reported in the registry record.

The record also lists other adverse events affecting 6 participants among 7 at risk in the abatacept arm and 3 among 3 at risk in the IV fluid arm. These broader event counts are distinct from the serious-event counts. The most frequent serious-event term listed is Infection, at 14.3%. The registry record does not provide enough detail in the stated details to attribute that term to a particular arm or to interpret its denominator. Death counts are not reported in the registry record.

Safety counts in a small pilot study are descriptive. They do not establish that an event rate is higher or lower in one arm, and the absence of a recorded serious event in an arm does not establish absence of risk. The registry record does not provide event-level timing, severity grading beyond the serious classification, relatedness judgments, or a detailed accounting of recurrent events. Those details are not reported in the registry record.

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

The posted primary-outcome data describe mean MRSS changes over 6 months in the abatacept and IV fluid arms. The means were -8.6 and -2.3, respectively, with standard deviations of 7.5 and 15.0. These summaries show the observed average change and the variation among the measurements represented in each arm. They do not provide a formal estimate of the treatment contrast or its precision.

The absence of a reported two-arm analysis is central to interpretation. The registry record says values are missing or not estimable for a continuous endpoint comparison. Without a reported contrast, confidence interval, or test result, the arm means should not be presented as proof that one assigned treatment changed MRSS more than the other. Nor does the lack of an inferential result establish that the arms were equivalent or that there was no difference. The registry record does not resolve either conclusion.

The trial's stated hypothesis concerned possible reduction in progression of skin thickening and fibrosis. The primary endpoint measures skin thickness using MRSS, but it does not capture the full range of systemic sclerosis manifestations. The registry record lists secondary measures involving oral aperture, hand extension, digital ulcerations, pulmonary function tests, and the Scleroderma Health Assessment Questionnaire; results for these measures are not reported in the registry record for this analysis. A conclusion about the primary score alone would not describe all aspects of the disease or the full set of outcomes.

Likewise, the safety summaries should be read as event counts in a small pilot study, not as definitive comparative safety estimates. The registry record does not report the detail needed to assess event timing, attribution, or a formal between-arm safety comparison. Overall, the results give a limited descriptive account of the posted outcome and adverse-event information. They do not establish efficacy, lack of efficacy, equivalence, or a definitive safety profile.

14. Why This Trial Matters Statistically

This study is statistically instructive because it pairs a randomized, masked design with a very small pilot enrollment and an incompletely reported outcome comparison. Randomization and masking are design features intended to reduce certain biases, but they do not remove the need for transparent reporting of the analysis, missing data, and uncertainty. The registry record identifies the design labels but does not give enough detail to assess their implementation.

The primary measure is continuous and is reported as arm means and standard deviations. Those summaries communicate both average change and variability, but they are not a substitute for the estimated between-arm contrast and its uncertainty. Here, the registry record specifically notes that the two-arm comparison is missing or not estimable. That makes it important to distinguish descriptive results from inferential conclusions rather than treating a visual or numerical difference between arm means as a tested result.

The study also illustrates the limits of using a pilot outcome to guide planning. The registry record describes an illustrative calculation based on a fraction of the observed effect, along with assumptions about significance level, allocation, and approximation. Such planning illustrates how future-study requirements depend on the target effect and variability. It does not indicate that the pilot had adequate power, nor does it turn an imprecise pilot estimate into a stable planning target.

Finally, multiple outcomes and incomplete reporting of missing-data and multiplicity methods affect how much can be learned from registry results. The record identifies secondary outcome topics but supplies no analysis entries for them. Clear reporting of analysis populations, outcome availability, model choices, and uncertainty would be necessary for a fuller statistical assessment. These issues are especially consequential when the primary comparison itself is not reported.

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 primary limitation is that the registry record does not report an estimable two-arm analysis for the continuous primary endpoint. The arm-level means and standard deviations cannot establish the size or precision of a treatment contrast. The record does not provide confidence intervals, a p-value, a test statistic, or the statistical model used for the primary comparison.

The reported outcome summaries are based on small arm sizes. This makes the estimates sensitive to the observed values and leaves limited information for characterizing variability. The record does not report individual data, baseline MRSS summaries, or a clinically meaningful-change threshold. It is therefore not possible to assess baseline score patterns, inspect the distribution of changes, or interpret the observed mean changes against a stated clinical threshold.

Important design and analysis details are not reported in the registry record, including eligibility criteria, the randomization procedure, which people were masked, the analysis population, and the handling of missing measurements. The record also does not state whether multiplicity was addressed across the primary and secondary outcomes. Results for the listed secondary measures are not reported in the registry record described for this analysis.

The study is labeled a pilot, but its protocol-level sample-size justification and detailed statistical plan are not reported in the registry record. The posted illustrative planning assumptions do not substitute for those details. Safety information is also limited: the record does not provide event-level timing, relatedness, or a formal comparison, and death counts are not reported in the registry record. These limitations mean that both effectiveness and safety findings remain descriptive rather than definitive.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: A Study to Evaluate the Safety and Efficacy of Abatacept in Patients With Diffuse Systemic Sclerosis (Scleroderma) — NCT00442611.
• Registry record last updated 2017-10-31; status last verified 2017-09.
• Results first posted 2015-04-24.
• 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 a completed randomized, triple-masked, parallel Phase 1 and Phase 2 pilot study sponsored by Stanford University. It enrolled 10 and compared weight-based intravenous abatacept with IV fluid placebo. Both interventions were scheduled for days 1, 15, 30 and monthly thereafter, for a total of 7 doses.

The primary outcome was change in MRSS at 6 months. The posted mean changes were -8.6 with a standard deviation of 7.5 in the abatacept arm and -2.3 with a standard deviation of 15.0 in the IV fluid arm. The registry record indicates that a two-arm continuous-outcome comparison is missing or not estimable. It does not report a formal primary comparison, confidence interval, or p-value.

Five secondary outcomes are listed, but their results and analyses are not reported in the registry record described for this analysis. The record posts serious and other adverse-event counts, but the small pilot and limited event detail do not support definitive comparative safety conclusions.