Study of the Medication Prazosin for Alcohol Dependence: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Study of the Medication Prazosin for Alcohol Dependence (NCT00762710), a randomized phase 2 study. The primary outcome is Alcohol Consumption.

2. Clinical Question

3. Trial Design

This was a phase 2, randomized, double-masked, parallel-group trial comparing prazosin medication with placebo medication. Random allocation is intended to make the assigned groups comparable on average, while masking is intended to reduce the influence of treatment knowledge on participants’ experiences, care, and outcome assessment. The registry identifies the design features but does not report the method used to generate or conceal the allocation sequence, or details about how masking was maintained.

The registry reports enrollment of 92. The stated schedule in both arms consisted of a 2-week titration, 10 weeks of stable dosing, and study visits at least weekly for 12 weeks. It also describes a final follow-up one month after the medication phase was discontinued. The primary outcome timeframe is 12 weeks, but the registry’s outcome description says Form 90 assessed alcohol and drug use for the preceding 90-day period at baseline and at the final medication visit. These descriptions do not specify in detail how the assessment periods were aligned with the treatment period.

The study is marked completed. Its listed start is 2008-01 and its primary completion is 2014-06. The sponsor is the Seattle Institute for Biomedical and Clinical Research. These administrative details describe the trial record; they do not provide evidence about the outcome of the treatment comparison. The registry lists one outcome measure but no analysis entries, and it does not report a usable estimate of the primary comparison in the information available for this trial.

The primary-outcome population is described as participants in each group who completed titration and provided baseline and last-week medication information. That is a specific population description, not a statement that all randomized participants contributed to the primary outcome. The record does not explain the allocation process, deviations from assigned treatment, or how participants who did not complete titration were handled in an analysis.

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: Of the 151 consented into the study, 59 did not go onto be randomized because of the following: Declined after screen (N=11) (includes missing baseline/first medication appointment) Ineligible at screen (N=48) * PTSD (N=11) * Acute illness (N=7) * Drug dependence (N=4) * Drinking inclusion not met (N=20) * Other (N=6)

Overall Study

Analysis population for the primary outcome, as defined in the registry: Providing baseline and last week of medication information for all participants that completed the titration period (40 in each group).

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 Alcohol Consumption, measured over 12 weeks.

The primary endpoint is alcohol consumption expressed as the percentage of days with heavy drinking. It is described as a mean continuous measure, with standard deviation as the measure of dispersion, and a 12-week timeframe. The registry says Form 90 was used at baseline and the final medication visit to assess alcohol and drug use over the preceding 90-day period. It also describes the primary-outcome population as participants who completed titration and had baseline and last-week-of-medication information.

A measure based on heavy-drinking days focuses on the frequency of heavy drinking rather than simply whether any drinking occurred. A mean gives a group-level summary of the measured outcome, while a standard deviation describes how spread out individual measurements are around that mean. Both can be useful for comparing groups: the mean addresses the average outcome, and the dispersion indicates how much participants’ measurements varied.

The registry’s description does not define the threshold used to classify a day as a heavy-drinking day, and that detail is not reported in the registry record. Nor does it specify the exact calculation used to turn the assessments into the endpoint comparison. Although the endpoint and its measurement instrument are identified, the posted record does not provide the group means, standard deviations, an effect estimate, or an uncertainty interval for the primary comparison. The endpoint’s relevance therefore can be described, but its observed result cannot be interpreted from the registry information available.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies the study as randomized, double-masked, and parallel-group. These design terms describe how the comparison was organized; they do not, by themselves, tell readers how the primary outcome was analyzed. The registry record does not report a statistical analysis plan or the method used to estimate the treatment contrast.

What does randomization contribute?

In general, random assignment helps balance both measured and unmeasured participant characteristics between groups across repeated use of the same design. It supports a causal comparison when assignment is implemented as intended and when the analysis respects the randomized groups. Randomization does not guarantee identical groups in a particular trial, and it does not address missing outcome data automatically. The registry labels allocation as randomized but does not describe sequence generation, concealment, stratification, or the analysis according to assignment.

What does masking contribute?

Double masking is intended to reduce bias arising when participants or study personnel know which treatment was assigned. This may matter for reported behavior and for study interactions. The registry identifies the masking category but does not describe which individuals were masked, how masking was maintained, or whether it was assessed. The label alone cannot establish that expectations or other influences were fully controlled.

How should the continuous endpoint be understood?

The primary outcome is described as the mean percentage of days with heavy drinking, with standard deviation. A mean summarizes the center of a set of measurements; the standard deviation describes their spread around that center. In a treatment comparison, the difference between group means is one common way to express an average contrast, but the registry does not report such a contrast for this outcome. It also does not state whether the analysis used change from baseline, a final measurement, repeated observations, or another summary. These possibilities can answer different questions and should not be assumed.

As a general statistical consideration, a percentage outcome is bounded and may have a distribution that is not well represented by a simple normal model, especially when observations cluster near a boundary. Analysts may examine the observed distribution and choose a model or summary suited to the data. The registry does not report distributional checks, model choice, transformations, or any approach to potential over-dispersion. Over-dispersion, in general, means that observed variability is greater than a model expects; accounting for it can affect uncertainty estimates. This is a general issue, not a claim that over-dispersion occurred in this trial.

What can a confidence interval or p-value add?

In general, an effect estimate describes the magnitude and direction of a comparison, and a confidence interval conveys its precision. A p-value addresses compatibility between the data and a specified null model under stated assumptions; it does not measure the probability that a treatment works, nor does it describe the importance of an effect. For this trial’s primary outcome, the registry does not report an estimate, confidence interval, or p-value. There is consequently no basis for interpreting statistical significance or precision.

What do planning assumptions mean?

The registry’s planning description specifies a two-sided significance level of 0.05, equal allocation, and a normal approximation, with the effect to detect expressed as a fraction of the observed effect. These are planning assumptions, not evidence that a particular sample size was justified in the original protocol or that the trial had a particular observed power. The record does not provide a sample-size justification or an original statistical plan. Any sample-size figures based on an observed effect would be planning illustrations, not observed power. The primary outcome’s missing single comparison also means that no observed effect for that endpoint can be interpreted from the registry information available.

Finally, a statistical method is only interpretable when the outcome definition, analysis population, model, and handling of incomplete data are clear. The registry provides the outcome’s broad definition and a population description, but not the analysis details needed to evaluate assumptions or reproduce the primary comparison. Those omissions limit the statistical conclusions that can be drawn, even though the trial design and endpoint are identified.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists one outcome measure, but it also states that the primary outcome has several categories or time points and was not reduced to one comparison. It lists no analysis entries. A single registered outcome label therefore does not mean that only one statistical test or one analysis was conducted. When multiple time points, categories, outcomes, or analyses are examined, the chance of finding an apparently notable result by chance can increase. Statistical approaches can account for multiplicity, but the registry record does not report whether any adjustment or prespecified hierarchy was used.

Missing-data handling is also not reported in the registry record. The primary-outcome population is described as participants who completed titration and provided baseline and last-week medication information, 40 in each group. The record does not say how many randomized participants lacked those measurements, why information might be missing, or whether any imputation or sensitivity analysis was used. These omissions matter because a complete-case comparison can be affected if the availability of measurements is related to participants’ outcomes or treatment experience.

The registry does not report whether the primary analysis followed intention-to-treat principles, analyzed participants as randomized, or used a different population. Nor does it explain how discontinuation, adherence, or protocol deviations were treated. Consequently, the exact population represented by any analysis cannot be established from the posted record. The stated population description should be read as the participants identified for the outcome information, not as proof of a particular statistical analysis set.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

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: inpatient alcohol detoxification (4.2%), death (2.3%), medical hospitalization (2.3%), medical hospitalization (2.1%).

The registry reports serious adverse events affecting 3 of 48 at risk in the prazosin group and 2 of 44 at risk in the placebo group. Other adverse events affected 28 of 48 at risk in the prazosin group and 15 of 44 at risk in the placebo group. Deaths are listed as 0 in the prazosin group and 1 in the placebo group. These are the registry’s group-level counts; they are not a primary alcohol-consumption result.

The record also lists serious-event terms with percentages: inpatient alcohol detoxification, 4.2%; Death, 2.3%; medical hospitalization, 2.3%; and Medical hospitalization, 2.1%. The registry does not explain the denominator or relationship between these term-level percentages and the group-level affected counts in the information available. The two hospitalization entries use different capitalization, and the record does not clarify whether they refer to separate coded terms.

Counts and listed terms do not establish that an event was caused by the assigned medication. They also do not describe event timing, duration, severity beyond the serious-event classification, or how events were adjudicated. The figures should be interpreted as safety reporting in the registry, not as proof of comparative risk or causation.

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

The record documents a randomized, double-masked comparison of prazosin with placebo and identifies alcohol consumption as the primary outcome. It describes the endpoint, measurement instrument, timeframe, and a population with outcome information. These details make the intended clinical question understandable: whether the assigned groups differed in the frequency of heavy-drinking days during treatment.

However, the posted registry information does not provide a single primary-outcome comparison. It says that the outcome has several categories or time points and was not reduced to one comparison, and it lists no analysis entries. No group means, treatment-effect estimate, confidence interval, or p-value is reported for the primary outcome. The record therefore does not show the direction, magnitude, or precision of an observed difference.

This absence must not be interpreted as evidence that the groups were the same, or as evidence that one group did better. A finding of no difference would require an analysis with an estimate and uncertainty; a claim of equivalence would require an appropriate design and prespecified margin. Neither is reported in the registry information available. Similarly, the fact that the trial is marked completed does not supply an outcome result.

The adverse-event figures provide a separate description of events reported for each group. They do not resolve the primary efficacy question, and the registry counts alone cannot establish whether treatment caused an event. The study’s design, endpoint, and safety listings can be described, but a treatment conclusion cannot be drawn without interpretable outcome results and sufficient information about the analysis.

Accordingly, the most defensible reading is limited: this completed phase 2 trial was designed to compare prazosin and placebo on heavy-drinking days, but the posted registry record does not allow a quantitative assessment of that comparison. Clinical conclusions should not be inferred from the design description or from the absence of a reported estimate.

13. Why This Trial Matters Statistically

This trial is statistically informative as an example of the difference between a clearly stated research question and a reportable treatment estimate. The registry identifies a randomized, double-masked comparison and defines a clinically relevant behavior-based endpoint. Those features describe the intended experiment, but they are not enough to evaluate the magnitude or precision of its findings.

Endpoint construction is particularly important in behavior measures. The registry refers to percentage of days with heavy drinking and identifies Form 90 assessments over a preceding 90-day period. It also specifies a 12-week timeframe and describes baseline and final medication information. Readers need to know how these assessment windows were translated into the final analysis measure, which comparison was primary, and how repeated or categorical information was handled. Those details are not reported in the registry record.

The trial also illustrates why an analysis population matters. Its outcome population is described as participants who completed titration and had the relevant measurements. Without a clear account of the randomized population, missing information, and analysis strategy, it is difficult to judge how representative an estimate would be, even if one were posted.

Finally, safety counts and efficacy results serve different purposes. The registry supplies serious and other adverse-event counts but does not provide the primary outcome comparison. Statistical interpretation requires each result to be connected to its endpoint, denominator, analysis population, and uncertainty. In this case, those principles point to a cautious conclusion: the design and question can be understood, while the primary treatment effect cannot be evaluated from the registry record.

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 most consequential limitation is that the registry does not report a single interpretable primary-outcome comparison. It identifies the endpoint but notes that it spans several categories or time points and is not reduced to one comparison. No analysis entries are listed. The absence of group summaries, an effect estimate, and uncertainty measures prevents assessment of the direction, size, or precision of any difference.

The endpoint description leaves important operational details unclear. Form 90 is named, and assessments are described for baseline and the final medication visit, covering the preceding 90-day period. The outcome timeframe is stated as 12 weeks, while the population description refers to baseline and last-week medication information. The registry does not explain how these elements were aligned or how the final endpoint value was calculated. The threshold defining a heavy-drinking day is also not reported in the registry record.

The analysis population is described as participants who completed titration and posted the specified outcome information, 40 in each group. The registry does not explain how participants without that information were handled, whether analyses followed randomized assignment, or how deviations and discontinuations were treated. It also does not report model assumptions, multiplicity procedures, or a prespecified analysis plan.

The registry’s adverse-event summaries have separate interpretive limits. They do not provide event timing or establish causation, and the relationship between term-level percentages and group-level counts is not clarified. These gaps do not invalidate the reported counts, but they limit what can be concluded from them.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Study of the Medication Prazosin for Alcohol Dependence — NCT00762710.
• Registry record last updated 2020-06-04; status last verified 2020-06.
• Results first posted 2020-06-04.
• 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.

18. Record Summary

NCT00762710 is a completed phase 2, randomized, double-masked, parallel-group study sponsored by the Seattle Institute for Biomedical and Clinical Research. It enrolled 92 and compared prazosin with placebo for alcohol dependence. Both arms are described as having a 2-week titration and 10 weeks of stable dosing, with visits at least weekly during the 12-week study period and a final follow-up one month after the medication phase.

The primary outcome was the mean percentage of days with heavy drinking, assessed using Form 90 and described with standard deviation. The registry identifies a population of participants who completed titration and had baseline and last-week medication information, 40 in each group. It does not report a single primary comparison or analysis entries, so the treatment effect and its precision cannot be interpreted from the posted record. Serious and other adverse-event counts are listed separately.