Tolcapone Treatment of Pathological Gambling: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Tolcapone Treatment of Pathological Gambling (NCT00927563), a na phase 2 study. The primary outcome is Clinical Global Impression Scale (CGI).

2. Clinical Question

3. Trial Design

The registry identifies NCT00927563 as “Tolcapone Treatment of Pathological Gambling,” with the official title “Tolcapone Treatment of Pathological Gambling: An Open-Label Study.” It is listed as a phase 2 study sponsored by the University of Chicago. The study status is completed; the recorded start is 2009-06 and primary completion is 2012-05.

The design is described as single-group, with allocation marked not applicable and masking listed as none. Tolcapone is the sole listed intervention, described at 100-300mg/day. The record lists enrollment of 24, but does not explain how many participants began treatment, completed follow-up, or contributed data to each outcome.

The registry’s stated goal is to evaluate efficacy and safety in pathological gambling. The primary outcome is the Clinical Global Impression Scale at Visit 5, identified as the final visit. The record also names the Yale Brown Obsessive Compulsive Scale Modified for Pathological Gambling and the Gambling Symptom Assessment Scale as secondary outcomes. Although three outcome measures are recorded, the record lists zero analyses.

Because there is no concurrent control group, the design can describe outcomes among participants assessed during the study but cannot by itself separate an intervention-associated change from other explanations for change over time. The record does not report a protocol, detailed schedule of assessments, eligibility criteria, or statistical analysis plan. Those design details should not be inferred from the study title or its stated aim.

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: Subjects could not be using concomitant use of psychotropic medications with possible effects on PG symptoms (i.e. antidepressants, opioid antagonists)(due to possible interference of results) or have had previous treatment with tolcapone.

Overall Study

Reasons for not completing this period:

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 Scale (CGI), measured over Visit 5 (final visit).

The primary endpoint is the Clinical Global Impression Scale (CGI), reported as a mean with standard deviation, in units on a scale. The record describes it as the clinician’s overall impression of the subject’s severity. Scores range from 1 to 7, with 1 indicating not ill at all and 7 indicating one of the worst cases seen. The CGI is assessed at visits 1-5, but the outcome specified for reporting is the score at Visit 5, the final visit.

A clinician-rated global measure can provide an overall judgment of clinical severity rather than a score focused on a single symptom. A mean gives a measure of the group’s central value, while the standard deviation describes the spread of individual scores around that mean. These summaries can help characterize the observed group, but they do not show the distribution of scores in full or explain why participants differ.

The registry record does not report the final-visit mean, standard deviation, number assessed, or a comparison with an earlier score. It therefore does not establish the direction or magnitude of any change in CGI scores. The score’s range and anchors explain what the measure is intended to represent; they are not themselves evidence about the study’s outcome.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry record describes the primary outcome as a continuous measure summarized by a mean and standard deviation. It does not report the outcome values, an analysis method, or an uncertainty estimate. The concepts below are general explanations of how these methods are commonly understood; they are not claims about analyses conducted in this study.

What does a mean describe?

General: A mean is a summary of the central level of a measured outcome across the observations included in an analysis. For the CGI, the record specifies a score on a scale from 1 to 7 and identifies the final visit as the primary assessment. A group mean would summarize the scores included at that visit, but it would not indicate that every participant had a score close to the mean. It also would not show the full distribution or identify individual trajectories.

The mean is interpretable in relation to the scale’s anchors. The registry describes 1 as not ill at all and 7 as one of the worst cases seen. Knowing a mean alone would not describe how scores were distributed between those anchors, and the record does not give the observed mean.

What does the standard deviation add?

General: The standard deviation describes the spread of observations around their mean. A larger standard deviation indicates more dispersion of observed values; a smaller one indicates that values are more concentrated around the mean. It is not the same as the standard error, which describes the precision of an estimated mean and depends on the number of observations analyzed. Neither quantity is reported for the primary outcome in the registry record.

A standard deviation is descriptive, not a measure of treatment effect. It does not show whether scores changed from baseline, and it does not distinguish intervention effects from other explanations for outcomes. To evaluate a mean difference or change, the relevant values, analysis population, and method would need to be reported. Those details are not reported in the registry record.

What would a confidence interval convey?

General: A confidence interval expresses the uncertainty around an estimated quantity under the assumptions of the statistical method used. An interval for a mean or mean change can communicate which values are compatible with the data and method. It is not a guarantee that the true value lies inside a particular calculated interval, nor does it resolve bias from an uncontrolled design. The registry record does not report a confidence interval for the CGI or the secondary outcomes.

A point estimate and its interval answer different questions: the estimate gives the central result, while the interval describes its statistical precision. Precision should not be confused with clinical importance. The meaning of a score difference also depends on the scale and context, neither of which is quantified further in the record.

How should the planning illustration be read?

The record describes a planning illustration based on the observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It specifies that the effect to detect is a stated fraction of the observed effect. Such calculations are planning scenarios, not results from participants. They are not observed power and do not establish that the study had a particular ability to detect an effect.

The assumed equal allocation between two arms does not match the registered single-group study. It should therefore be read as a hypothetical planning framework, not as a description of the trial’s actual design. The record does not report the trial’s own sample-size justification or design assumptions. It also does not report the observed effect needed to evaluate the basis for the illustration.

General: Planning calculations depend on assumptions about the outcome, variability, effect size, statistical test, and study design. If those assumptions differ from the eventual data or design, the planning estimate may not describe the study’s actual precision. A sample-size illustration cannot substitute for the trial’s observed results, uncertainty estimates, or a clearly reported analysis.

Why does the single-group design matter?

General: A concurrent control group can help distinguish changes associated with an intervention from changes that might have occurred without it. A single-group study lacks that direct comparison. Repeated observations may describe the course of scores over time, but interpreting a difference requires the observation times, available participant data, and analysis method. The registry record does not report these details for the primary endpoint beyond identifying the final visit.

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("Tolcapone")
n   <- c(22)
m   <- c(2.88)
sp  <- c(1.3)
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  Tolcapone  22  2.880  1.300  2.304  3.456

11. Multiplicity, Missing Data and Analysis Populations

The registry lists three outcome measures: the CGI as primary, and the Yale Brown Obsessive Compulsive Scale Modified for Pathological Gambling and Gambling Symptom Assessment Scale as secondary outcomes. It records zero analyses. The registry record does not report a statistical analysis plan, which outcome comparisons were intended, or whether any adjustment for multiple testing was planned or performed.

General: When several outcomes or comparisons are examined, the chance of finding an apparently notable result by chance can increase. Statistical approaches can address this issue, but their appropriateness depends on which outcomes and comparisons were planned and how they were analyzed. Without an analysis plan and reported results, it is not possible to determine how multiplicity was handled in this study. The outcome list alone does not establish that all listed measures were analyzed.

Missing-data methods and analysis populations are also not reported in the registry record. Enrollment is recorded as 24, but the number with a final-visit CGI assessment is not reported. The record does not explain withdrawals, missed visits, exclusions, or whether analyses included all enrolled participants or only those with available measurements. These omissions matter because the analyzed group may differ from the enrolled group, and the interpretation of a mean depends on which observations contributed to it.

The registry record does not state whether any interim analyses were planned or conducted, nor does it provide a statistical analysis plan. Those details cannot be inferred from the study’s phase, completion status, or listed outcomes. In the absence of reported analysis methods, missing-data handling, and population definitions, the registered endpoint cannot be linked to a reproducible estimate of the outcome.

12. Safety Results

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

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry lists 0 affected among 24 at risk for serious adverse events in the tolcapone group. It lists 10 affected among 24 at risk for other adverse events. These are the counts recorded for the listed categories; they should not be read as a comparison with another group, because the study is registered as single-group and no comparator is listed.

The serious adverse event terms are not listed in the registry record. The deaths field is not reported in the registry record, so it should not be interpreted as a count of zero. The record also does not provide event-level details such as timing, duration, severity, outcome, or attribution to tolcapone. A count of affected individuals does not indicate how many events each person experienced.

General: Safety counts describe what was recorded under the registry’s categories and reporting practices. They do not, by themselves, establish that an event was caused by an intervention or quantify comparative risk. Interpretation is limited when event definitions, follow-up completeness, and comparator data are unavailable. The safety figures should therefore be read as descriptive registry counts, not as a controlled estimate of risk.

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

The registry record establishes that this was a completed, open-label, single-group study of tolcapone in pathological gambling, with enrollment of 24. It identifies a final-visit CGI score as the primary outcome and names two secondary measures. It also records adverse-event counts for the tolcapone group. These details describe the registered study and its intended measurements.

The record does not report the primary outcome result, secondary outcome results, or statistical analyses. It therefore does not show the observed CGI mean, its variability, any score change, or the precision of an estimated effect. Although the study’s stated goal was to evaluate efficacy and safety, that goal is not itself a finding. No conclusion about whether scores improved or worsened, or by how much, can be drawn from the outcome information reported in this registry record.

The single-group design also limits causal interpretation. General: Without a concurrent control group, an outcome observed after an intervention cannot by itself establish what would have happened over the same period without that intervention. A change in a measure, even if reported, may have more than one explanation. The record does not supply the comparator needed to estimate a controlled treatment effect.

The safety information is similarly descriptive. The record lists no serious adverse events as affected in the group, while it lists affected individuals for other adverse events. It does not report serious event terms or a death count. These figures do not provide a comparative safety estimate or details of event severity and attribution.

Thus, the available information is useful for understanding the study’s question, design, outcome definitions, and recorded safety counts. It is not enough to assess the magnitude or precision of an efficacy result, to establish a causal effect, or to characterize safety comprehensively. Those conclusions require outcome and analysis details that are not reported in the registry record.

14. Why This Trial Matters Statistically

This study is statistically informative as an example of the distinction between a registered research question and a reported result. The record describes an open-label, single-group study and names a clinician-rated primary endpoint at the final visit. Those details tell readers what investigators intended to measure, but they do not provide the observed endpoint values or an analysis.

The design also makes the role of comparison especially clear. General: A single-group study can describe measured outcomes among its participants, but a concurrent control group provides a reference for separating intervention-associated changes from other changes over time. The registered design has no such comparator. This limits what causal claims could be supported even if changes were reported.

The record also illustrates why outcome definitions and reporting completeness matter. The CGI’s scale range and anchors are stated, and two secondary measures are named, but the registry does not report the results or analysis methods. Without the outcome estimates, their variability, and information about who contributed data, readers cannot judge precision or assess whether the results are representative of the enrolled group.

Finally, the planning illustration is distinct from the actual study design and from observed evidence. Its assumptions describe a hypothetical two-arm framework, whereas the registered study is single-group. General: Sample-size planning helps define a study under specified assumptions; it does not replace outcome reporting or measure the study’s observed power.

The central statistical lesson is that a completed status, stated aim, and defined endpoint do not substitute for analyzable results. For this record, the design and reporting limitations are essential context for interpreting what can—and cannot—be learned from the registry information.

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.

Several limitations are specific to the information recorded for this study. First, the study is open-label and single-group, with no concurrent comparator. As a result, the record does not describe a controlled basis for separating any observed change from other influences. The lack of a control group is a design feature, not a statistical adjustment that can be resolved from the information.

Second, the primary endpoint is specified at Visit 5, but its observed mean and standard deviation are not reported in the registry record. The number assessed at the final visit is also not reported. Without those values, readers cannot assess the outcome level, spread, or precision. The record also does not report baseline values or a comparison between baseline and final assessment.

Third, although secondary measures are listed, their results are absent, and the record lists zero analyses. The statistical analysis plan, handling of missing data, and analysis populations are not reported. It is therefore unclear which observations would contribute to each endpoint or how any incomplete follow-up would be treated.

The description of the intervention gives a dose range of 100-300mg/day but does not report adherence, actual exposure, or dose changes. The registry record does not provide further participant characteristics or eligibility criteria, limiting assessment of whom the results might represent. For safety, serious adverse event terms are not listed, and the deaths field is not reported. Event timing, severity, and attribution are also absent.

These limitations concern both the single-group design and the incompleteness of reported outcome and analysis details. They prevent a precise assessment of efficacy and constrain interpretation of the recorded safety counts.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Tolcapone Treatment of Pathological Gambling — NCT00927563.
• Registry record last updated 2023-02-23; status last verified 2023-02.
• Results first posted 2014-03-06.
• 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

NCT00927563 is a completed phase 2, open-label, single-group study titled “Tolcapone Treatment of Pathological Gambling.” The sponsor is the University of Chicago. The registry records enrollment of 24 and describes tolcapone at 100-300mg/day. The stated aim was to evaluate efficacy and safety in pathological gambling.

The primary outcome is the CGI mean and standard deviation at Visit 5, the final visit. The registry also names two secondary outcomes, but lists zero analyses. The primary and secondary outcome results, analysis methods, missing-data handling, and analysis populations are not reported in the registry record.

For safety, the record lists 0 affected among 24 at risk for serious adverse events and 10 affected among 24 at risk for other adverse events. Serious event terms are not listed, and the deaths field is not reported. The single-group design provides no concurrent control comparison.