This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for D-Cycloserine Enhancement of Exposure in Social Phobia (NCT00633984), a randomized phase 4 study. The primary outcome is Liebowitz Social Anxiety Scale (LSAS).
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00633984 |
| Phase | Phase 4 |
| Condition | Social Anxiety Disorder |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Triple |
| Enrollment | 169 |
| Arms in the primary outcome | 2 |
| Lead sponsor | Massachusetts General Hospital |
| Results posted | Yes |
2. Clinical Question
Population
People with social anxiety disorder, also called social phobia in the registry description. The record describes persistent fear of social or performance situations and avoidance that can affect quality of life and relationships. Further eligibility details are not reported in the registry record.
Intervention
Cognitive Behavioral Group Therapy combined with 50mg D-Cycloserine. The drug was intended to be added to the behavioral therapy.
Comparator
Cognitive Behavioral Group Therapy combined with 50mg Placebo. Both groups therefore received the group therapy intervention, with D-Cycloserine or placebo as the accompanying drug intervention.
Primary question
At Week 13, what were the mean Liebowitz Social Anxiety Scale scores in the group receiving D-Cycloserine and the group receiving placebo alongside therapy? The registry record posts group means and 95% confidence intervals; it does not post a comparative test result.
The trial addresses whether adding D-Cycloserine to cognitive behavioral group therapy is associated with a different social-anxiety symptom score than adding placebo to the same type of therapy. The outcome is a continuous scale score, so the posted comparison concerns group averages rather than the proportion of participants who met a response or remission definition. Although the scale description defines remission as a score < 30, remission results are not reported in the registry record.
The record describes the study as randomized and parallel, with triple masking. It reports enrollment of 169 participants. The registry description does not specify further population characteristics, the randomization procedure, or which groups of people were masked. Those details are not reported in the registry record.
3. Trial Design
This was a randomized, parallel-group, Phase 4 study of D-Cycloserine enhancement of exposure in social phobia. The record lists Massachusetts General Hospital as the sponsor and Social Anxiety Disorder as the condition. The study started in 2007-03, reached primary completion in 2012-03, and is listed as completed. Enrollment was 169.
The two listed groups received Cognitive Behavioral Group Therapy plus 50mg D-Cycloserine or Cognitive Behavioral Group Therapy plus 50mg Placebo. Thus, the comparison is an adjunctive-treatment contrast: the behavioral group therapy was part of both arms, while the accompanying drug intervention differed. The registry record does not report the number of therapy sessions, their schedule, or other delivery details.
Randomization means participants were assigned to groups by a chance-based process, in contrast to choosing treatment based on participant or clinician preference. In general, random assignment can help make groups comparable on average, including for characteristics that were not measured. It does not ensure that the groups are identical, and it does not by itself resolve questions about adherence, missing outcome data, or how an analysis handled participants after assignment. The particular randomization method and allocation ratio are not reported in the registry record.
The study is described as triple masked. The record does not identify which parties were masked or explain how masking was maintained, so the label cannot be used to infer the roles of participants, therapists, outcome assessors, or analysts. The registry record also does not report the protocol’s planned analysis methods, sample-size justification, interim analyses, or rules for handling deviations from assigned treatment.
At Week 13, the posted primary outcome includes 87 participants in the D-Cycloserine group and 82 in the placebo group. The meaning of those outcome counts in relation to the full enrollment, including any losses or exclusions, is not specified in the registry record. There are 2 outcome measures listed, but no secondary outcome results are posted.
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
| Stage | Cognitive Behavioral Group Therapy + 50mg D-Cycloserine | Cognitive Behavioral Group Therapy + 50mg Placebo |
|---|---|---|
| STARTED | 87 | 82 |
| COMPLETED | 78 | 69 |
| NOT COMPLETED | 9 | 13 |
Reasons for not completing this period:
| Reason | Cognitive Behavioral Group Therapy + 50mg D-Cycloserine | Cognitive Behavioral Group Therapy + 50mg Placebo |
|---|---|---|
| Lost to Follow-up | 0 | 6 |
| Withdrawal by Subject | 8 | 7 |
| Hospitalized | 1 | 0 |
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.
| Characteristic | Unit | Cognitive Behavioral Group Therapy + 50mg D-Cycloserine | Cognitive Behavioral Group Therapy + 50mg Placebo | Total |
|---|---|---|---|---|
| Participants analysed | 87 | 82 | 169 | |
| Age, Continuous | years | 34.6 (SD 10.5) | 30.5 (SD 9.8) | 32.6 (SD 10.4) |
| Sex: Female, Male: Female | Participants | 31 | 42 | 73 |
| Sex: Female, Male: Male | Participants | 56 | 40 | 96 |
| Region of Enrollment: United States | participants | 87 | 82 | 169 |
6. Primary Endpoint
The registry lists the primary outcome as Liebowitz Social Anxiety Scale (LSAS), measured over Week 13.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | 95% Confidence Interval |
| Unit | units on a scale |
| Endpoint classification | Continuous Endpoint |
The primary endpoint is the Liebowitz Social Anxiety Scale (LSAS) at Week 13, reported as a mean score in units on a scale with a 95% confidence interval. The LSAS is described as a 24-item measure of fear and avoidance in social and performance situations during the last week. Each item is rated from 0-3 for fear and avoidance, and the scale has a possible score of 144.
The scale is used to quantify symptoms across a range rather than to record only whether a person does or does not have social anxiety. A continuous score can preserve distinctions among participants whose symptom levels differ, and group means provide a concise summary of the average score in each arm. The score’s interpretation still depends on its measurement properties, the population, and the clinical context; the registry record does not report a threshold for a meaningful between-group difference.
The scale description gives severity bands: 55-65 for moderate social phobia, 65-80 for marked social phobia, 80-95 for severe social phobia, and Greater than 95 for very severe social phobia. It also defines remission as a score < 30. The posted primary result is a group mean, not an individual participant’s classification, and the record does not post remission counts. A mean cannot show how scores were distributed around it or how many participants fell within a particular band.
The outcome timeframe is Week 13. The registry record does not report whether that timing was chosen to assess a particular treatment stage or how the measure was administered. The interpretation should therefore remain focused on the reported score and its uncertainty, rather than assuming additional information about assessment procedures.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
At Week 13, the mean LSAS score was 39.19 in the Cognitive Behavioral Group Therapy + 50mg D-Cycloserine arm, based on 87 participants, with a 95% confidence interval from 34.79 to 43.59. In the Cognitive Behavioral Group Therapy + 50mg Placebo arm, the mean was 42.44, based on 82 participants, with a 95% confidence interval from 37.94 to 47.03. The posted group means are descriptive summaries of the observed outcome values.
The D-Cycloserine group’s reported mean is lower than the placebo group’s reported mean. The confidence intervals describe uncertainty around each arm’s mean, not a confidence interval for the difference between arms. They overlap, but that fact alone does not determine whether a formal between-group comparison would be statistically significant. The registry record does not post a comparative estimate, a p-value, or a test result for this outcome.
A confidence interval is a range of values compatible with the observed data under the statistical procedure used to construct it. In general, a narrower interval indicates greater precision for the quantity being estimated, while a wider interval indicates more uncertainty. These intervals concern the separate arm means. Without a reported interval for the between-arm contrast, the precision of that contrast cannot be read directly from the two arm-specific intervals.
The scale description gives score bands and a remission definition, but the reported means alone do not establish how many individuals improved, worsened, or met remission criteria. Nor do they show the distribution of individual scores, changes from baseline, or differences in outcome among subgroups. Baseline scores and changes from baseline are not reported in the registry record.
The results should be read as a Week 13 description of the two groups, not as a complete account of the trial’s statistical analysis. The registry record does not report whether the sponsor’s analysis adjusted for baseline values or other variables, how it handled missing observations, or whether it used an intention-to-treat population. No claim about statistical significance or a causal magnitude of effect can be made from the posted arm means alone.
The comparison also has a specific scope: both groups received cognitive behavioral group therapy, and the contrast was D-Cycloserine versus placebo as the added intervention. These results do not directly compare therapy with no therapy, and the registry record does not post outcomes for other treatment combinations. The clinical importance of the observed means cannot be determined from a threshold for meaningful change because such a threshold is not reported in the registry record.
In short, the posted summaries show the two group means and their uncertainty at Week 13. They do not provide the comparative statistical test or enough information to reconstruct the full analysis. Any interpretation beyond those descriptive results would require details that are not reported in the registry record.
9. Statistical Methods Explained
The registry record reports a continuous primary outcome, summarized with a mean and 95% confidence interval in each arm. It also identifies the study as randomized, parallel, and triple masked. These are useful design descriptors, but they do not specify the complete statistical methods used to analyze the outcome.
What does a mean summarize?
In general, a mean is the arithmetic average of the observed scores in a group. It gives a compact summary of the group’s central level on a continuous measure. A mean does not describe the full distribution: participants may have scores above or below it, and different distributions can produce the same mean. The registry record does not post individual scores, standard deviations, or other measures of spread for the LSAS outcome.
The arm summaries report the D-Cycloserine group mean as 39.19 and the placebo group mean as 42.44. The accompanying 95% confidence intervals are 34.79 to 43.59 and 37.94 to 47.03, respectively. These are intervals for the arm-specific means, as presented in the record. No separate confidence interval for the difference between groups is posted.
What does a 95% confidence interval mean?
In general, a confidence interval is generated by a statistical procedure that accounts for sampling uncertainty. A 95% confidence level describes the long-run coverage property of that procedure when its assumptions hold: across repeated applications in comparable settings, intervals constructed in this way would contain the target quantity at the stated rate. It is not a statement that there is a 95% probability that this particular fixed mean lies inside the calculated interval.
Confidence intervals help show the precision of estimates. They do not, on their own, identify whether a treatment difference is clinically important, whether the study’s assumptions are satisfied, or whether missing observations could have changed the result. The registry record does not identify the exact method used to calculate these intervals or report diagnostics for its assumptions.
Why is the between-group estimate important?
For a randomized comparison, the central comparative quantity is often an estimate of how the outcome differs between assigned groups. A direct estimate and its confidence interval would show the direction and precision of the contrast in a way that separate arm intervals do not. A formal test may also be reported, but a p-value alone would not communicate the size or precision of an effect. Here, the registry record posts arm means and intervals but does not report a between-arm estimate or p-value, so the formal comparative uncertainty is unavailable.
Randomization supports comparison of assigned groups, but the analysis still matters. For example, baseline adjustment, the definition of the analysis population, and the treatment of missing outcomes can affect the estimate and its uncertainty. The record does not report these analysis details, so no particular approach should be assumed.
What is over-dispersion, in general?
Over-dispersion is a general concern for some outcome models when observed variability is greater than the model assumes. If a model understates variability, standard errors can be too small and confidence intervals can be too narrow. This concept is most directly relevant to outcomes modeled as counts or categories; the primary outcome is described as a continuous scale score, and the registry record does not state that an over-dispersion model was used. It would therefore be inappropriate to infer an over-dispersion issue or a correction from the posted information.
What do planning calculations represent?
Planning calculations use assumptions about the design and an effect to detect to illustrate the amount of information a future study might need. They are not observations from participants and are not the same as the number enrolled. The registry description of the planning illustration states a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation; it also describes the target effect as a stated fraction of the observed effect. The actual planning values are not reported in the registry record.
Such calculations are planning illustrations, not observed power. They do not show the probability that a treatment works, and they cannot replace an estimate with its uncertainty. The record does not report the trial’s own sample-size justification, so the planning illustration should not be interpreted as evidence about the original design rationale.
Overall, the available methods information supports a descriptive reading of the arm-level means and confidence intervals. The registry record does not report the statistical model, the handling of baseline measures, the analysis population, or a comparative hypothesis test. Those omissions limit how fully the posted estimates can be evaluated.
10. Multiplicity, Missing Data and Analysis Populations
The record lists 2 outcome measures and posts a primary outcome result, but it reports 0 secondary outcomes posted. It does not describe a full hierarchy of outcomes, a multiplicity adjustment, or which analyses were designated as confirmatory. A multiplicity plan is not reported in the registry record.
In general, multiplicity arises when several outcomes, time points, groups, or analyses are tested. The more opportunities there are to find an apparently unusual result, the more important it is to understand which comparisons were planned and how the analysis controlled the overall error rate. This general issue does not establish that the trial did or did not make additional comparisons; the statistical analysis plan is not reported in the registry record.
Missing-data methods are also not reported. The record gives outcome counts of 87 for the D-Cycloserine group and 82 for the placebo group, alongside overall enrollment of 169, but it does not explain how these counts relate to all randomized participants or whether any outcome values were missing. It does not state whether missing values were imputed, excluded, or addressed using another method.
The analysis population is not reported in the registry record. In general, an intention-to-treat analysis retains participants in the groups to which they were randomized, while other analysis populations may use different inclusion rules. The registry record does not identify which approach was used, whether adherence affected inclusion, or how protocol deviations were handled. These details matter because the analysis population and missing-data assumptions can influence both the estimate and its uncertainty.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Cognitive Behavioral Therapy + DCS | 0 | 87 | 0.0% |
| Cognitive Behavioral Therapy + Placebo | 0 | 82 | 0.0% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Cognitive Behavioral Therapy + DCS | 26 of 87 |
| Cognitive Behavioral Therapy + Placebo | 19 of 82 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Cognitive Behavioral Therapy + DCS | Cognitive Behavioral Therapy + Placebo |
|---|---|---|---|
| General | General disorders | 7 of 87 | 4 of 82 |
| Other | General disorders | 6 of 87 | 5 of 82 |
| Neurological | General disorders | 6 of 87 | 4 of 82 |
| GI | General disorders | 5 of 87 | 4 of 82 |
| Cognitive/Emotional | General disorders | 3 of 87 | 1 of 82 |
| Genitourinary | General disorders | 0 of 87 | 1 of 82 |
The serious adverse event summaries list 0 affected participants among 87 at risk in the Cognitive Behavioral Therapy + DCS group and 0 among 82 at risk in the Cognitive Behavioral Therapy + Placebo group. No serious adverse event terms are listed. The death counts are not reported in the registry record.
These figures are counts for the groups and outcome summaries posted in the registry record. They do not, by themselves, establish that no serious events occurred outside the recorded reporting framework, nor do they give details about event definitions, observation periods, or adjudication. Those details are not reported in the registry record.
The record also lists 26 participants affected by other adverse events among 87 at risk in the D-Cycloserine group, and 19 among 82 at risk in the placebo group. These are counts, not a severity comparison or a statistical test. The record does not provide event-level descriptions in the posted summary, so the types, timing, and duration of these other events cannot be assessed from these figures alone.
Safety counts should be read separately from the primary LSAS outcome. The registry record does not report a formal comparison of adverse-event risk or enough information to interpret differences in event patterns. These summaries describe what is posted; they do not establish a broader safety profile.
12. What the Result Does, and Does Not, Mean
The posted primary outcome describes mean LSAS scores at Week 13 for participants assigned to cognitive behavioral group therapy with D-Cycloserine or with placebo. The D-Cycloserine arm’s mean was 39.19, with a 95% confidence interval of 34.79 to 43.59; the placebo arm’s mean was 42.44, with a 95% confidence interval of 37.94 to 47.03. The registry record does not post a direct estimate or test of the between-arm difference.
These results do not show the individual pattern of change. A group mean cannot tell whether most participants had similar scores, whether a smaller number of very high or low scores influenced the average, or how many participants improved. Baseline values, change scores, response results, and remission counts are not reported in the registry record.
The LSAS description supplies severity bands and defines remission as a score < 30. The posted mean is a group-level summary, not a classification of every participant. It therefore cannot establish how many individuals had scores in any severity band or met the remission definition. The registry record also does not report a threshold for a clinically meaningful difference in the group means.
The trial’s contrast is limited to D-Cycloserine versus placebo when each was paired with cognitive behavioral group therapy. It does not estimate the effect of the therapy compared with no therapy, and it does not address other treatment combinations. Interpretation also depends on design and analysis details—such as missing-data handling and the analysis population—that are not reported in the registry record.
For these reasons, the posted values are best understood as descriptive arm-level results with uncertainty around each mean. They do not by themselves establish a statistically significant or clinically important comparative effect. Such conclusions would require a reported between-arm analysis and additional context about the statistical plan and outcome handling.
13. Why This Trial Matters Statistically
This trial illustrates why a randomized design and a reported outcome summary are not the whole statistical story. Random assignment provides a basis for comparing the groups, and the parallel design makes the treatment contrast easy to describe: both arms received cognitive behavioral group therapy, with D-Cycloserine or placebo added. The posted LSAS means then show the average score in each arm at Week 13.
Precision is also central. The registry record reports a 95% confidence interval for each arm mean, making the uncertainty around those individual summaries visible. However, the key comparative question concerns the difference between arms. Without a reported estimate and confidence interval for that contrast, the posted arm summaries do not convey the comparative precision directly. This distinction is important when interpreting any trial that reports group-specific outcomes without a direct comparison.
The record also demonstrates the importance of transparent analysis reporting. The number of participants contributing to each posted arm summary is listed, but the relation of these outcome counts to enrollment and the handling of missing values are not explained. The analysis population, statistical model, and multiplicity procedures are not reported. Those details are relevant for judging how the estimates were produced and whether they address the intended trial question.
Finally, the outcome is a continuous symptom scale, while readers may be interested in clinically interpretable categories such as remission. A group mean does not provide remission frequency or individual-level change. The scale description includes a remission definition, but no remission results are posted. This distinction reinforces a general statistical lesson: the information in an average, an individual threshold, and a treatment contrast is related but not interchangeable.
14. 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 main limitation for interpreting this trial record is that the primary result is reported as separate arm means and confidence intervals without a direct between-arm estimate, confidence interval, or p-value. The posted values describe each group, but do not fully quantify the comparative effect or its precision.
Baseline LSAS scores and changes from baseline are not reported. The record therefore does not show whether the groups began with similar average scores or how the Week 13 scores relate to baseline. The analysis population, model, and handling of missing outcome data are also not reported. Although the record lists 87 participants in the D-Cycloserine arm and 82 in the placebo arm for the primary outcome, it does not explain how those counts relate to the total enrollment of 169.
The registry record does not report the randomization method, allocation ratio, detailed eligibility criteria, or which parties were masked under the triple-masking designation. It also does not report the therapy schedule, adherence, or protocol deviations. These omissions limit evaluation of how participants entered and remained in the analysis and how the assigned interventions were delivered.
The record lists 2 outcome measures but posts 0 secondary outcome results. It does not report a multiplicity plan, the trial’s own sample-size justification, or interim analyses. The posted primary outcome is a Week 13 mean; there are no reported response, remission, or individual-level results, despite the remission definition in the scale description. The serious adverse event summary lists no affected participants in either arm, but event definitions and observation details are not reported in the registry record.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: D-Cycloserine Enhancement of Exposure in Social Phobia — NCT00633984.
- Registry record last updated 2014-05-14; status last verified 2014-04.
- Results first posted 2014-05-14.
- 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.
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18. Record Summary
NCT00633984 is a completed, randomized, parallel, triple-masked Phase 4 study sponsored by Massachusetts General Hospital. It enrolled 169 participants with Social Anxiety Disorder and compared Cognitive Behavioral Group Therapy plus 50mg D-Cycloserine with Cognitive Behavioral Group Therapy plus 50mg Placebo. The study started in 2007-03 and reached primary completion in 2012-03.
The primary posted outcome is the mean Liebowitz Social Anxiety Scale score at Week 13. The D-Cycloserine arm had a mean of 39.19, with a 95% confidence interval of 34.79 to 43.59, among 87 participants. The placebo arm had a mean of 42.44, with a 95% confidence interval of 37.94 to 47.03, among 82 participants. A direct comparative estimate and test are not reported in the registry record.
The record lists 2 outcome measures, with 0 secondary outcomes posted. Serious adverse events affected 0 participants in each group; death counts are not reported in the registry record. Important details about the analysis population, missing data, statistical model, multiplicity, and sample-size justification are not reported in the registry record.