Prazosin for Treating Noncombat Trauma Post-Traumatic Stress Disorder: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Prazosin for Treating Noncombat Trauma Post-Traumatic Stress Disorder (NCT00183430), a randomized na study. The primary outcome is Clinical Global Impression of Change.

2. Clinical Question

3. Trial Design

This was a randomized, parallel-group trial with quadruple masking, according to the registry record. The two described arms were prazosin plus psychotherapy and placebo plus psychotherapy. The record lists the study phase as NA. The sponsor was the Seattle Institute for Biomedical and Clinical Research.

The listed enrollment was 20. That figure is the registry enrollment entry; the outcome results separately show 3 participants analyzed in the prazosin group and 11 in the placebo group. The registry says that the number analyzed for the primary measure equals the number able to complete that assessment at Week 8. The listed enrollment should therefore not be interpreted as the number contributing primary outcome data.

The study start is recorded as 2003-10 and primary completion as 2009-05. Its status is TERMINATED. The reason for termination, whether recruitment or follow-up was completed as planned, and the timing of termination are not reported in the registry record. The record does not describe the randomization sequence, allocation concealment, masking procedures, treatment duration beyond the primary outcome timeframe, or whether any participants changed assigned treatment.

The primary outcome timeframe was baseline to Week 8. The posted results provide a mean and standard deviation for each arm. No inferential analysis is posted, and no analysis population beyond the assessment-completion definition is described. The registry lists three outcome measures overall, but the details of the other measures are not part of the primary result. No protocol-level statistical plan is reported in the registry record.

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: no significant events.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Number of participants analyzed equals the number of participants who were able to complete this assessment at Week 8.

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 Clinical Global Impression of Change, measured over Baseline to Week 8.

The primary endpoint was the Clinical Global Impression of Change, a clinician-rated global measure of change compared with baseline. Its seven response levels range from markedly improved to markedly worse, with no change at the midpoint. This scale is intended to capture whether overall well-being and functioning have changed in a way that is meaningful and distinct, rather than measuring a single symptom in isolation.

The registry describes the endpoint as evaluated from baseline to Week 8. It reports the outcome in units on a scale and summarizes each group with a mean and standard deviation. The scale direction matters when reading those means: lower scores correspond to more improvement, while higher scores correspond to more worsening. A score at the no-change category provides a reference for interpreting the group summaries, but a group mean does not show how many individual participants improved, stayed the same, or worsened.

The registry defines the number analyzed as the number able to complete the assessment at Week 8. It does not report separate baseline and Week 8 values, individual participant responses, or a distribution across the response categories. The measure is used because a global rating can reflect change in overall functioning and well-being; it does not, by itself, identify which symptoms or aspects of functioning account for a rating.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary result is a continuous outcome summarized by a mean and standard deviation in each group. A mean describes the arithmetic center of the observed scores. A standard deviation describes how spread out scores are around that mean. These summaries are useful for describing each analyzed group, but they are not, by themselves, a complete comparison of the groups. The posted results do not include a test or interval estimate for the contrast.

What would an uncertainty interval add?

General statistical explanation: a confidence interval gives a range of values compatible with the data and a specified statistical procedure. For a treatment comparison, an interval would communicate the precision of the estimated contrast as well as its direction. A narrow interval would indicate greater precision than a wide interval, although an interval still depends on the assumptions and analysis used to construct it. No confidence interval for the primary comparison is reported in the registry record, so its precision cannot be read directly from the posted means and standard deviations.

Why is the outcome scale direction important?

The endpoint is a seven-point global change scale, with 1 denoting markedly improved, 4 denoting no change, and 7 denoting markedly worse. Lower ratings therefore represent more improvement on this measure. The group means can be interpreted against those category meanings, but a mean is not an individual response category. It does not show the number of participants in each category or whether the mean reflects a broadly similar response or a mix of very different responses. The registry does not report those individual-level distributions.

What can the standard deviations tell us?

The standard deviations describe observed variability within the analyzed groups. They do not measure the uncertainty of a treatment effect in the same way as a confidence interval for a between-group contrast. General statistical explanation: uncertainty about a group mean or contrast depends on both variability and the amount of information available. This is why the standard deviations should be read alongside the group counts, and why the small analyzed group in particular limits how much can be inferred from its summary. No separate variance model or distributional assessment is reported.

Why is there no recalculated comparison?

The registry record indicates that values are missing or not estimable for a two-arm comparison of this continuous endpoint. It reports no analysis results, and the registry entries do not include a sponsor-reported test or adjusted treatment estimate. Accordingly, there is no recalculated unadjusted comparison to describe. A fresh calculation from group summaries would not supply the missing analysis plan, would not address incomplete outcome data, and would not establish which estimand the trial intended to estimate. The sponsor’s own analysis does not appear as a posted result in the registry record.

How should planning illustrations be understood?

General statistical explanation: a sample-size planning illustration asks how much information a future study might need under stated assumptions. The registry’s description says its planning approach uses the observed effect, a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation; the target effect is a stated fraction of the observed effect. Such an illustration is not an observed power calculation and is not evidence that the completed trial was adequately powered. Its interpretation depends on the assumptions, including the observed effect used for planning. The registry record does not report the trial’s own sample-size justification or whether these assumptions were part of its original design.

General statistical explanation: over-dispersion means that observed variability is greater than a chosen model expects. When present, standard errors based on an overly restrictive variance assumption can be too small, making uncertainty appear less than it is. The posted primary endpoint is continuous and is reported with standard deviations; the record does not report an over-dispersion assessment or a variance adjustment. This concept should not be taken to mean that over-dispersion was present in this trial.

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("Prazosin", "Placebo")
n   <- c(3, 11)
m   <- c(2.33, 3.27)
sp  <- c(0.58, 0.9)
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  Prazosin  3  2.330  0.580  0.889  3.771
CARM  Placebo  11  3.270  0.900  2.665  3.875

11. Multiplicity, Missing Data and Analysis Populations

The registry lists three outcome measures overall and reports zero secondary outcomes posted. It also reports zero analyses. The record does not identify a multiplicity procedure, a hierarchy among outcomes, or a plan for controlling the chance of false-positive findings across multiple analyses. With no inferential results posted, there are no reported p-values for the primary or other outcomes to interpret. The registry record does not establish whether additional analyses were performed outside the posted results.

For the primary endpoint, the analysis population is described as participants able to complete the assessment at Week 8. The reported counts are 3 in the prazosin group and 11 in the placebo group. The registry does not explain why other enrolled participants are not represented in those endpoint counts, whether the participants were randomized before exclusion from analysis, or whether any missing assessments were imputed. Reasons for missing outcomes and the handling of missing data are not reported in the registry record.

These omissions matter because analysis restricted to assessment completers can differ from an analysis that includes all randomized participants under a defined missing-data approach. General statistical explanation: when outcome availability is related to a participant’s condition, treatment experience, or other factors, complete-case summaries can represent a selected subset. That possibility cannot be confirmed or ruled out from the registry information.

The record does not state whether the primary analysis followed an intention-to-treat principle, whether treatment adherence was considered, or how protocol deviations were handled. It also does not describe imputation, sensitivity analyses, or interim analyses. None of these methods should be assumed to have been used.

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 reports zero serious adverse events among the 3 participants at risk in the prazosin group and zero among the 11 participants at risk in the placebo group. These are the serious-event counts recorded for the stated risk groups. The record lists no serious adverse event terms. Death counts are not reported in the registry record.

Other adverse events are reported for 2 of 3 participants in the prazosin group and 8 of 11 participants in the placebo group. These counts should be kept distinct from the serious adverse event counts: they describe the registry’s other-adverse-event category, not serious events. The record does not provide event-level descriptions for these other events, their severity, timing, duration, or relationship to assigned treatment.

Safety counts in small groups are descriptive. A zero serious-event count does not establish that serious events could not occur, and the listed counts do not support a precise comparison of safety between arms. The registry does not report further detail about monitoring, event definitions, or whether all participants contributed safety information for the same duration. These figures describe what was posted, not a complete account of every possible safety outcome.

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

The registry offers a limited account of a randomized comparison of prazosin plus psychotherapy with placebo plus psychotherapy in a noncombat-trauma PTSD study. For the primary outcome, it reports group means and standard deviations among participants who completed the Week 8 assessment. The scale’s direction makes lower scores more favorable in terms of rated change, but the posted summaries are descriptive and do not include an inferential comparison.

The results do not establish the size or precision of a treatment effect. No test, confidence interval, or adjusted estimate is reported, and the record identifies no completed analyses. The mean scores cannot show how many individuals improved or worsened, and the standard deviations do not replace an uncertainty estimate for the contrast. The registry entries also do not explain why the endpoint analysis groups were smaller than the listed enrollment.

The study status is TERMINATED, but the reason is not reported in the registry record. Without that information, the termination should not be attributed to a particular result, safety issue, recruitment problem, or administrative decision. The record likewise does not provide enough information to characterize missing outcomes or determine how they might affect the observed summaries.

General statistical explanation: a randomized design is intended to support a fair comparison by assigning participants to groups, but the strength of conclusions also depends on outcome completeness, analysis methods, and precision. The registry entry identifies randomization and masking but does not provide the details needed to assess those processes fully. The posted findings therefore describe the available endpoint data; they do not, on their own, settle whether the groups differed beyond the observed summaries or whether the results would generalize to other populations.

14. Why This Trial Matters Statistically

This trial is statistically informative as an example of the difference between a planned randomized comparison and the information available in a registry result. Randomization and quadruple masking are recorded design features, but the posted primary result consists of group-level descriptive summaries, with no inferential analysis. Readers can see the scale direction and the reported scores, yet cannot assess the precision of a between-group estimate from a confidence interval or test because neither is reported.

The endpoint analysis counts also illustrate why enrollment and outcome denominators should not be treated as interchangeable. The listed enrollment is 20, while the primary outcome population is defined by Week 8 assessment completion and the posted group counts are 3 and 11. The registry does not explain the difference. That gap limits interpretation of who the observed means represent and how missing outcome information might affect the comparison.

The record also separates an endpoint summary from a full statistical analysis plan. It does not report the trial’s sample-size justification, handling of missing data, multiplicity approach, or interim analyses. These details are important for understanding how an analysis was intended to be conducted and how much confidence to place in a reported estimate. Their absence means they cannot be reconstructed from the group means and standard deviations.

Finally, the safety entries show why counts need context. Serious adverse event counts are zero in both groups, while other adverse event counts are also recorded. Small denominators and absent event detail limit what those figures can establish. The trial’s posted record supports careful description, but not a strong conclusion about comparative effects or safety.

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 outcome analysis includes only participants able to complete the Week 8 assessment, according to the registry definition. The record gives group counts but does not report reasons for non-completion, the number randomized to each arm, or how missing outcomes were handled. It is therefore not possible to determine whether the analyzed participants represent all randomized participants or whether missingness could affect the observed means.

The endpoint summaries are based on small analyzed groups, and no inferential comparison is posted. There is no confidence interval, p-value, treatment-effect estimate, or description of an analysis model. The reported means and standard deviations do not provide individual response distributions, baseline values by arm, or a separate account of change for each participant.

The registry marks the study TERMINATED but does not report why it ended. The listed enrollment is 20, but the record does not explain how enrollment relates to the primary endpoint analysis counts. The reason for any difference, and whether the planned recruitment or follow-up was completed, are not reported in the registry record.

Important design and conduct details are also absent, including dose and schedule, randomization and masking procedures, treatment adherence, psychotherapy content, and protocol deviations. The registry does not report a sample-size justification, missing-data plan, multiplicity strategy, or interim-analysis plan. These details should not be inferred from the randomized and quadruple-masked labels alone.

Safety interpretation is limited by the lack of event descriptions, timing, severity, and treatment relationship for other adverse events. Death counts are not reported in the registry record. Together, these limitations mean that the available information supports a description of posted outcomes, but not a complete appraisal of the trial’s conduct or the precision and robustness of its treatment comparison.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Prazosin for Treating Noncombat Trauma Post-Traumatic Stress Disorder — NCT00183430.
• Registry record last updated 2018-06-14; status last verified 2018-06.
• Results first posted 2012-11-27.
• 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 NCT00183430, a randomized, quadruple-masked, parallel-group trial of prazosin plus psychotherapy versus placebo plus psychotherapy for PTSD associated with noncombat trauma in individuals taking selective serotonin reuptake inhibitors. Listed enrollment is 20, the status is TERMINATED, and the phase is recorded as NA. The study start is 2003-10 and primary completion is 2009-05.

The primary outcome is the Clinical Global Impression of Change from baseline to Week 8. The registry reports a mean of 2.33 (standard deviation 0.58) for 3 participants assigned to prazosin and a mean of 3.27 (standard deviation 0.9) for 11 assigned to placebo. No inferential analyses are posted. Serious adverse event counts are zero in each group; other adverse events are reported for 2 of 3 and 8 of 11 participants, respectively. The reason for termination, missing-data handling, and death counts are not reported in the registry record.