Switching Anti-TNF-Alpha Agents in Rheumatoid Arthritis (RA): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Switching Anti-TNF-Alpha Agents in Rheumatoid Arthritis (RA) (NCT00796705), a randomized phase 4 study. The primary outcome is Change in the Disease Activity Score Using C-reactive Protein (DAS28[CRP]) From Baseline to Week 12 in Non-Switchers Versus Switchers..

2. Clinical Question

The study addresses a treatment-strategy comparison for people whose rheumatoid arthritis had not responded adequately to a TNF-alpha inhibitor. Its primary outcome is a continuous measure of disease activity, so the central descriptive comparison is the mean change in score in the non-switcher and switcher groups. The record reports a mean change of -1.4 for non-switchers and -1.7 for switchers. These are group summaries, not an inferential estimate of the difference between strategies.

The registry also lists outcomes based on DAS28[CRP] thresholds at Week 12, a decrease in the score, and ACR response criteria. The record does not post analysis results for those secondary outcomes. The trial is marked terminated, and the registry record does not explain the reason for termination. The clinical question can therefore be described, but the posted information does not establish whether the strategies differ statistically or what the results imply for treatment decisions.

3. Trial Design

The registry describes a randomized, double-masked, parallel-group phase 4 study. Enrollment is listed as 13, and the status is terminated. The study began in 2008-11, with primary completion in 2010-10. The sponsor is the National Institute of Allergy and Infectious Diseases (NIAID). The registry record does not report why the study was terminated or give further details about the conduct of randomization or masking.

The comparison is between continuing an existing TNF-alpha inhibitor and switching to the alternative agent. The non-switcher group is described as receiving adalimumab or etanercept. The switcher group is described as changing from adalimumab to etanercept or from etanercept to adalimumab. The arm descriptions specify subcutaneous injections over 12 weeks; for adalimumab and placebo, injections are described as blinded and alternating. The registry does not provide enough detail to infer additional features of the dosing or allocation procedures.

For the primary outcome, the posted groups are Non-Switcher/Adalimumab or Etanercept and Switcher/Adalimumab to Etanercept or Etanercept to Adalimuma. The respective group sizes are 7 and 6. Their mean changes in DAS28[CRP] are -1.4 and -1.7, with standard deviations of 0.9 and 1.09. The record identifies the primary analysis population as intent-to-treat.

Six secondary outcomes are listed, covering low disease activity, remission, a decrease in DAS28[CRP], and ACR 20, ACR 50, and ACR 70 responses at Week 12. The record lists no analyses for these outcomes. It does not report a sample-size justification, a detailed statistical analysis plan, allocation concealment procedures, or a schedule of interim analyses.

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: Each subject signed an informed consent prior to undergoing any screening procedures. At the screening visit, subjects underwent procedures to establish inclusion/exclusion criteria.

Overall Study

Analysis population for the primary outcome, as defined in the registry: Intent-to-treat

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 the Disease Activity Score Using C-reactive Protein (DAS28[CRP]) From Baseline to Week 12 in Non-Switchers Versus Switchers., measured over Baseline, Week 12.

The primary endpoint is change in the Disease Activity Score using C-reactive protein, DAS28[CRP], from baseline to Week 12. It is reported as a mean with a standard deviation, and its unit is scores on a scale. The registry identifies the primary outcome population as intent-to-treat.

DAS28 is described as a composite score on a scale from 0 to 10. It incorporates the number of tender joints out of 28, the number of swollen joints out of 28, serum C-reactive protein in mg/L, and the participant’s assessment of disease activity on a 100 mm visual analogue scale. The registry description identifies scores >5.1 as high disease activity, scores <=3.2 as low disease activity, and scores <2.6 as remission.

A change score expresses how the measured score at follow-up differs from its baseline value; a negative mean change indicates a decrease in the score over the measurement period. A continuous endpoint preserves information about the amount of change rather than reducing the outcome to whether a participant crossed a threshold. A group mean describes the average change, while the standard deviation describes variability among participant-level changes around that mean.

DAS28[CRP] is used to summarize several aspects of rheumatoid arthritis disease activity in one measure. That composite can help characterize the overall pattern of change, but it does not show which component contributed to a change in the total score. The posted primary results do not include confidence intervals or an inferential comparison, so they describe the group averages and their variability without quantifying the precision of the between-group contrast.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a mean change describe?

For a continuous endpoint, a mean change summarizes the average participant-level change in a group. In this study, the outcome is change in DAS28[CRP] from baseline to Week 12. The posted mean changes are -1.4 among non-switchers and -1.7 among switchers. A negative sign indicates a decrease in the score. The group mean does not reveal whether most participants had similar changes or whether a smaller number of larger changes influenced the average.

The standard deviation is a measure of spread among individual observations around the group mean. The posted standard deviations are 0.9 and 1.09 for the non-switcher and switcher groups, respectively. A standard deviation is not a confidence interval and does not directly express uncertainty about the mean or the difference between groups. It describes variability in the observed participant-level changes.

Why compare groups rather than means alone?

The clinical question concerns the contrast between continuing and switching, not simply whether either group’s average changed from baseline. A direct comparative analysis would estimate how the outcomes differ between the assigned strategies and describe uncertainty around that estimate. The registry record gives the group-level means and standard deviations but lists no analyses. A between-group estimate, its confidence interval, and its p-value are not reported in the registry record.

In general, a confidence interval gives a range of values compatible with the observed data and the assumptions of the analysis. Its width reflects precision: a wider interval indicates greater uncertainty about the estimated effect. A p-value, when used, assesses the compatibility of data with a specified null hypothesis under the analysis assumptions; it does not measure the size or clinical importance of an effect. Neither type of inferential result is posted for the primary comparison, so neither should be inferred from the group summaries.

What does randomization contribute?

In general, random allocation aims to make the comparison less vulnerable to systematic differences in participant characteristics at the start of a trial. It does not guarantee that groups will be balanced on every characteristic, particularly when the groups are small. The record identifies the study as randomized, double-masked, and parallel-group, but it does not describe the randomization sequence, allocation concealment, or details of masking. Those procedures are therefore not reported in the registry record.

A parallel-group design assigns participants to a strategy and follows the assigned groups over the study period. The posted endpoint compares change from baseline to Week 12. The record does not explain how adherence, treatment changes, or departures from assigned treatment were incorporated into the primary analysis. The primary population is identified as intent-to-treat, but further operational details are not reported.

How should variability and precision be understood?

Continuous outcomes can show variation among participants. In general, the standard deviation helps describe that variation, while the standard error and confidence interval are used to describe uncertainty in an estimated mean or contrast. These quantities answer related but different questions. A large spread among participant outcomes can coexist with a relatively well-estimated mean in a sufficiently informative study; conversely, a small study can leave substantial uncertainty even when the observed group averages look different.

Over-dispersion is a general concern when observed variation is greater than a statistical model expects. A model that understates variability may produce overly narrow uncertainty intervals or overly optimistic tests. The registry record does not report a model, a variance assessment, or an adjustment for over-dispersion. Given the limited group sizes, the mean and standard deviation are useful descriptive summaries, but they do not show whether model assumptions would be adequate for an inferential analysis.

What do the sample-size calculations mean?

Sample-size calculations in this setting are planning illustrations based on the observed effect, not evidence that the study had a particular probability of detecting an effect. The stated assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. Calculations are framed around detecting a stated fraction of the observed effect. A figure labelled participants per arm for 80% power is a planning quantity under those assumptions, not observed power and not a result from the trial.

Observed power is not a substitute for an uncertainty interval around an estimated effect. In general, planning estimates depend on the assumed effect size, variability, significance level, and desired power. When an observed effect from a small study is used as the planning basis, the estimate can be unstable. The registry record does not report that these planning assumptions were the original design assumptions, and they should not be interpreted as the trial’s prespecified sample-size justification.

What can be inferred from the registry analysis record?

The registry lists 0 analyses. This means that the posted record does not supply inferential analysis results for the primary comparison. It does not establish that no analysis was conducted outside the registry; details of any such analysis are not reported in the registry record. For interpretation of the posted results, the group summaries remain descriptive, and no recalculated comparison should be substituted for a sponsor analysis. The record does not mark a discrepancy between the posted summaries and a sponsor analysis.

In general, recalculations from summary statistics are unadjusted and cannot reproduce an analysis that uses participant-level data, covariates, missing-data methods, or other model features. They can also rely on assumptions that are not verifiable from group summaries alone. The posted information does not include a recalculated primary comparison, so the appropriate conclusion is to describe the available means and standard deviations without presenting a new test or estimate.

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("Non-Switcher/ Adalimumab or Etanercept", "Switcher/ Adalimumab to Etanercept or Etanercept t")
n   <- c(7, 6)
m   <- c(-1.4, -1.7)
sp  <- c(0.9, 1.09)
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  Non-Switcher/ Adalimumab or Etanercept  7  -1.400  0.900  -2.232  -0.568
CARM  Switcher/ Adalimumab to Etanercept or Etanercept t  6  -1.700  1.090  -2.844  -0.556

11. Multiplicity, Missing Data and Analysis Populations

The registry lists six secondary outcomes: DAS28[CRP] low disease activity at Week 12, DAS28[CRP] remission at Week 12, a decrease in DAS28[CRP] greater than 1.2 from baseline to Week 12, and ACR 20, ACR 50, and ACR 70 responses at Week 12. Numerical results for these outcomes are not reported in the registry record. The record does not describe a multiplicity adjustment or identify a hierarchy among the secondary outcomes.

In general, testing several outcomes creates more opportunities for chance findings than focusing on a single prespecified comparison. A multiplicity strategy can help control the interpretation of those tests, for example by defining which outcomes are primary or adjusting inference across a family of comparisons. Without a reported strategy and without posted secondary analyses, these outcomes cannot be used to support claims about statistical significance.

The primary outcome population is identified as intent-to-treat. This label generally refers to analyzing participants according to randomized assignment, but the registry does not state how the analysis handled participants with missing Week 12 measurements, deviations from assigned treatment, or incomplete follow-up. The number of missing primary endpoint observations and the methods used to address missing data are not reported in the registry record. Missingness should not be assumed either to have occurred or not to have occurred based on the posted summaries.

The record also does not report a detailed statistical analysis plan, interim analyses, or the timing of any analysis decisions. These omissions limit assessment of prespecification and the potential influence of analytic choices. The terminated status is recorded, but the reason for termination and its relationship, if any, to analysis or follow-up are not reported in the registry record.

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 5% reporting threshold.

Most frequent non-serious adverse event terms

The registry lists serious adverse event counts separately for four groups. In the Non-Switcher/Adalimumab group, 0 serious adverse events are listed among 3 at risk. In the Non-Switcher/Etanercept group, 0 are listed among 4 at risk. In the Switcher/Adalimumab to Etanercept group, 0 are listed among 4 at risk. In the Switcher/Etanercept to Adalimumab group, 0 are listed among 2 at risk.

These figures describe the counts entered in the registry for the listed groups. They do not establish that a serious event was impossible, and they do not support a precise comparative safety estimate. The number at risk is small in each listed group, and the record does not provide confidence intervals or a statistical comparison for serious adverse events.

For other adverse events, the registry lists 3 affected among 3 at risk in the Non-Switcher/Adalimumab group, 3 among 4 in the Non-Switcher/Etanercept group, 4 among 4 in the Switcher/Adalimumab to Etanercept group, and 2 among 2 in the Switcher/Etanercept to Adalimumab group. These are counts, not evidence that the groups differ in risk. Death counts are not reported in the registry record. The record lists no top serious-event terms.

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

The posted primary results show a decrease in mean DAS28[CRP] from baseline to Week 12 in both randomized groups: -1.4 among non-switchers and -1.7 among switchers. The associated standard deviations are 0.9 and 1.09, and the group sizes are 7 and 6. These summaries describe the observed group-level changes and the spread of observations within each group.

They do not quantify the uncertainty around the contrast between groups. No confidence interval, p-value, adjusted estimate, or formal test is reported in the registry record. The difference in the direction or magnitude of the posted means is not, by itself, evidence that one strategy is superior. Nor do the data establish that the strategies are equivalent: an equivalence or non-inferiority framework and its required analysis are not reported.

The endpoint is a composite measure of rheumatoid arthritis disease activity. A mean change in this score does not show how every participant changed, which component of the composite contributed to the result, or how many participants reached the registry’s low-disease-activity or remission thresholds. Although those threshold outcomes and ACR response outcomes are listed as secondary measures, their numerical results are not reported in the registry record.

The randomized, double-masked design describes the intended trial structure, but the registry record does not provide enough detail to assess implementation, missing outcome data, adherence, or the analysis procedures. The trial is marked terminated, and the reason is not reported. Those limitations matter when interpreting the posted summaries, particularly because the groups are small and no inferential analysis is posted.

The result is therefore best understood as a descriptive account of the recorded mean changes over the stated period. It neither establishes a causal comparative effect with quantified precision nor supports a treatment recommendation. It also cannot resolve whether the observed changes are representative of a broader population of adults with rheumatoid arthritis who have an inadequate response to these agents.

14. Why This Trial Matters Statistically

This trial raises a clinically relevant statistical question: how to compare continuing a TNF-alpha inhibitor with switching to an alternative agent after an inadequate response. The randomized, double-masked, parallel design is intended to make a direct comparison possible. The primary outcome is continuous, allowing the registry to describe the average change in disease activity rather than reporting only a threshold classification.

At the same time, the record illustrates the difference between descriptive results and comparative inference. Group means and standard deviations communicate the observed summaries, but they do not provide an estimate of uncertainty around the contrast. Without an inferential analysis, readers cannot determine how compatible the observed summaries are with a range of possible between-group effects. Statistical interpretation needs both an effect estimate and a measure of its precision, as well as an understanding of the assumptions used.

The small group sizes make careful reporting especially important. General principles of statistical inference indicate that small samples can yield imprecise estimates and that individual observations can strongly influence group summaries. That makes transparent reporting of participant-level flow, missing data, analysis methods, and confidence intervals valuable. Those details are not reported in the registry record.

The listed secondary outcomes also show why planning for multiplicity matters. Multiple disease-activity thresholds and response definitions can describe different aspects of an outcome, but interpreting several tests without a prespecified strategy can be misleading. Here, the registry lists those outcomes but does not post their results or a multiplicity approach. The record thus highlights the need to distinguish an outcome’s presence in a protocol or registry from evidence that its result supports a conclusion.

The main statistical lesson is not a claim about which strategy is preferable. It is that a randomized comparison needs transparent estimates, uncertainty measures, and analysis details to support a precise interpretation. The posted results allow a descriptive comparison, while leaving the comparative inference unresolved.

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 registry marks the study terminated but does not report why it ended. It does not describe whether termination affected recruitment, follow-up, outcome collection, or the planned analysis. Enrollment is listed as 13, and the primary outcome summaries are based on groups of 7 and 6. The record does not provide participant flow or explain whether these group sizes represent all randomized participants or those with available primary outcome data.

The primary outcome is identified as intent-to-treat, but the handling of missing Week 12 measurements is not reported. The record also does not report adherence, withdrawals, protocol deviations, or the method used to define change when a measurement was unavailable. These omissions limit assessment of the population represented by the posted summaries and the possible influence of incomplete follow-up.

Although the study is described as randomized and double-masked, the registry does not report the sequence-generation method, allocation concealment, or details of how masking was maintained. No statistical analysis plan, sample-size justification, interim-analysis plan, or inferential result is posted. The record lists six secondary outcomes but does not report their results or a method for handling multiplicity.

The primary results provide group means and standard deviations, but no confidence interval or formal comparison. As a result, the precision of the between-group contrast is unknown from the registry record. The means alone cannot show participant-level distributions, threshold attainment, or the contributions of the components of DAS28[CRP]. The safety counts are also sparse, and death counts are not reported in the registry record.

These limitations do not change the descriptive values that are posted, but they narrow the conclusions those values can support. In particular, they prevent a well-quantified comparative interpretation and leave important questions about trial conduct, missing data, and analysis methods unanswered.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Switching Anti-TNF-Alpha Agents in Rheumatoid Arthritis (RA) — NCT00796705.
• Registry record last updated 2012-10-04; status last verified 2012-08.
• Results first posted 2012-08-13.
• 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

NCT00796705 is a randomized, double-masked, parallel-group phase 4 trial of switching TNF-alpha inhibitors versus continuing an existing agent in adults with rheumatoid arthritis and an inadequate response. Enrollment is listed as 13; the status is terminated. The primary endpoint is change in DAS28[CRP] from baseline to Week 12 in an intent-to-treat population.

The registry posts mean changes of -1.4 (standard deviation 0.9) for non-switchers and -1.7 (standard deviation 1.09) for switchers, with group sizes of 7 and 6. It lists six secondary outcomes but no analyses. A formal comparison, confidence interval, p-value, missing-data methods, and reason for termination are not reported in the registry record. The posted primary values are descriptive and do not establish a precise comparative effect.