Cannabidiol Treatment of Cognitive Dysfunction in Schizophrenia: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Cannabidiol Treatment of Cognitive Dysfunction in Schizophrenia (NCT00588731), a randomized phase 2 study. The primary outcome is Verbal Short Term Memory.

2. Clinical Question

3. Trial Design

This was a Phase 2 randomized, parallel-group trial comparing cannabidiol with placebo as an addition to stable antipsychotic medication. The registry describes the study as fixed dose and quadruple-masked. Its brief description characterizes the treatment period as six weeks. The registry lists schizophrenia and schizoaffective disorder as the conditions under study and reports enrollment of 41 participants.

The listed groups are cannabidiol and placebo. The adverse-event record gives 21 participants at risk in the cannabidiol group and 20 in the placebo group. These are the group counts for the safety entries; the registry record does not provide further details about allocation procedures or explain whether every enrolled participant contributed data to each efficacy analysis.

The study start is recorded as 2009-02, and primary completion as 2013-12. Its status is completed. Yale University is listed as the sponsor. The record does not report the cannabidiol dose, treatment adherence, concomitant-treatment rules beyond stable antipsychotic medication, or the operational details of masking. It also does not provide a sample-size justification or a fuller account of the protocol. Those omissions limit how much can be inferred about the conduct and intended precision of the trial from the registry entry alone.

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

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.

Population: A total of 36 participants completed all aspects of the study. Higher T-scores represent better outcomes.

6. Primary Endpoint

The registry lists the primary outcome as Verbal Short Term Memory, measured over 6 weeks.

The primary endpoint is verbal short term memory, assessed at 6 weeks with the Hopkins Verbal Learning Test. The registry describes the instrument as having three trials. Each trial has a maximum total score of 12, with a range of 0-12; the maximum across all three trials is 36, with a range of 0-36. The reported endpoint is not that raw total, however. It is expressed as a t-score.

The record describes these t-scores as normalizing scores relative to a representative sample, with a mean of 50. A higher t-score represents better verbal learning. This direction matters when interpreting a group contrast: higher values correspond to better performance on the measured cognitive task, without by themselves establishing why any difference arose.

A cognitive test can provide a structured way to quantify performance in a defined domain. Verbal short term memory is one such domain, while overall cognition is listed as a secondary outcome measured on the MATRICS Battery. The registry record does not provide details about the clinical interpretation of a particular score change or a threshold for meaningful change. It also does not give a single numerical between-group result for the primary endpoint, so the posted information does not establish the size or precision of a difference at 6 weeks.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a randomized comparison aim to estimate?

In general, a randomized trial compares outcomes between groups assigned to different strategies. The treatment contrast is the difference or other specified comparison between the groups’ outcome distributions. For a continuous endpoint such as a t-score, analyses commonly summarize group values with means and a measure of variability, then estimate a contrast with uncertainty. The registry identifies the primary outcome parameter as a mean and its dispersion as a standard deviation. However, the actual primary comparison, its uncertainty, and its inferential result are not reported in the registry record as one result.

Random allocation is intended, in general, to make the groups comparable in expectation at the point of assignment. It does not guarantee identical groups, especially in a trial with 41 participants. The record says allocation was randomized but does not report the sequence-generation method, concealment procedures, or baseline values needed to describe observed comparability. The group counts in the safety entries are 21 and 20.

What does masking contribute?

In general, masking means that specified people involved in a trial do not know which intervention a participant received. This can help limit expectation-related influences on care, reporting, assessment, and analysis. The registry labels the trial quadruple-masked, but it does not identify the masked roles or describe how masking was implemented. The label therefore describes the recorded design, while the practical details remain unreported.

How should a confidence interval be understood?

In general, a confidence interval expresses the uncertainty around an estimated effect under the assumptions of the statistical method used. A narrower interval indicates greater statistical precision than a wider interval, but precision alone does not establish clinical importance. An interval spanning values on both sides of no difference may be compatible with effects in either direction, depending on its limits and the analysis. No primary-outcome estimate or confidence interval is reported as a single comparison in the registry record, so these interpretive steps cannot be applied to a specific efficacy result.

What do the planning assumptions mean?

The planning illustration described for the study uses a two-sided significance level of 0.05, equal allocation between groups, and a normal approximation. It is framed around detecting a stated fraction of the observed effect. Such calculations are planning illustrations rather than observed trial results. In general, a planning calculation asks how many participants would be needed under chosen assumptions to have a specified chance of detecting an effect. It does not measure the probability that the observed result is true, and it is not observed power. The registry record does not report the trial’s own sample-size justification, and the planning framework should not be mistaken for the original design rationale.

In general, planning estimates that use an effect observed in a trial are sensitive to that estimate. When the observed effect is imprecise, a planning illustration based on it is also uncertain. Considering a fraction of an observed effect can examine alternative planning targets, but it does not turn those targets into observed effects or establish what the trial was designed to detect. The registry record does not state the protocol’s targeted effect or its sample-size assumptions.

Why does the outcome structure matter?

The registry indicates that the primary outcome has several categories or time points and is not reduced to one comparison. In general, an analysis must define which time point, score, or contrast answers the primary question. Different choices can correspond to different estimands and can lead to different uncertainty. The record identifies verbal short term memory at 6 weeks but does not provide a single numerical comparison to summarize. It also lists overall cognition measured on the MATRICS Battery as a secondary outcome. Details of the reported secondary analysis are not included in the registry record.

In general, variability describes how dispersed individual measurements are around a group summary. For a continuous outcome, a standard deviation is a descriptive measure of that spread. If data are markedly skewed or contain influential observations, the mean and standard deviation may not fully characterize the distribution; methods may then require careful assessment or alternatives. These are general considerations, not claims about the trial’s observed data. The registry identifies the mean and standard deviation as the primary outcome summary but does not report distributional diagnostics or model details.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists two outcome measures and two analyses, and identifies verbal short term memory as the primary outcome. Overall cognition measured on the MATRICS Battery is listed as a secondary outcome. The primary outcome entry indicates that several categories or time points exist and that they are not reduced to one comparison. The registry record does not report how those categories or time points were selected for analysis, or whether a single comparison was designated as the main inferential test.

In general, multiplicity arises when several outcomes, time points, subgroups, or statistical tests are considered. Without an appropriate plan, examining multiple results can increase the chance of finding an apparently notable result by chance. Methods such as prespecifying a primary contrast or adjusting inference can address some multiplicity concerns. The registry record does not report a multiplicity strategy, an adjustment method, or a hierarchy for interpreting the listed analyses. Their absence from the record does not establish that none existed; it means the approach is not reported in the registry record.

Information about missing data and analysis populations is also not reported in the registry record. In particular, the registry entries do not state how many participants had primary endpoint measurements, how missing measurements were handled, or whether the main analysis followed assignment regardless of treatment received. The safety counts should not be treated as efficacy-analysis denominators. Without those details, readers cannot assess the potential effect of missing outcomes or determine precisely which participants contributed to an efficacy estimate.

Blinding, randomization, and a clearly specified analysis population are distinct aspects of trial interpretation. The record identifies randomization and quadruple masking, but does not provide enough statistical-plan detail to assess the analysis choices. These gaps matter when considering how robust an estimated treatment contrast would be, if one were available.

11. 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 records serious adverse events for 0 of 21 participants in the cannabidiol group and 0 of 20 participants in the placebo group. It records other adverse events for 15 of 21 participants in the cannabidiol group and 17 of 20 participants in the placebo group. These are participant counts in the registry’s safety categories, not estimates of a causal treatment effect.

A count of zero recorded serious adverse events does not show that an intervention is free of risk. In general, safety counts need to be interpreted in light of the number of participants observed, the duration of follow-up, how events were defined and collected, and whether participants completed follow-up. The record describes a six-week treatment period, but further details about event ascertainment and follow-up are not reported in the registry record.

The category of other adverse events is distinct from serious adverse events in the posted entries. The counts do not indicate severity for each event, whether a participant experienced more than one event, or whether an event was judged related to treatment. Deaths are not reported in the registry record. These safety entries therefore support a limited descriptive reading of recorded counts, not a comprehensive comparison of harms or a conclusion about causation.

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

The registry record establishes the broad clinical question: whether adding cannabidiol or placebo to stable antipsychotic medication was compared in a randomized, masked, parallel-group study of people diagnosed with schizophrenia or schizoaffective disorder. It also defines the primary cognitive measure, its direction, and the 6-week assessment time. Those details help readers understand what outcome the trial intended to assess.

The posted information does not provide a single numerical between-group result for the primary endpoint. It therefore does not support a statement about whether the recorded verbal short term memory scores favored either group, how large any contrast was, or how precisely it was estimated. The record’s note that the outcome includes several categories or time points is important: a named endpoint alone is not enough to reconstruct a specific treatment comparison.

The endpoint is a test-based measure expressed as a t-score, with higher values representing better verbal learning. It is not, on its own, a complete account of cognition or of participants’ broader functioning. The MATRICS Battery is listed for overall cognition as a secondary outcome, but its numerical result is not included in the registry record used for this interpretation.

The recorded safety counts describe adverse events observed in the two groups, but do not establish that treatment caused or prevented them. Zero serious adverse events recorded in either group does not establish absence of risk, and the other-event counts alone do not describe event type, severity, relatedness, or duration.

Accordingly, the available registry entries are most useful for understanding the study design and the intended measurement. They do not permit a quantitative judgment about the primary efficacy result, its precision, its clinical importance, or the balance of benefits and harms. Those questions require outcome estimates and analysis details that are not reported in the registry record.

13. Why This Trial Matters Statistically

This trial is statistically instructive because the registry contains meaningful design and endpoint information while leaving the primary comparison unresolved in the posted record. The distinction between an outcome’s definition and its result is essential. Knowing that verbal short term memory was measured at 6 weeks, and knowing that higher t-scores represent better verbal learning, does not reveal the observed difference between groups.

The entry also illustrates why a stated design label is not a substitute for analysis details. Randomization and quadruple masking describe important features of the planned comparison, but interpretation also depends on the estimand, analysis population, missing-data handling, and uncertainty around the estimate. These details are not reported in the registry record. Their absence limits assessment of how the efficacy analysis was conducted.

Multiplicity is another relevant statistical issue. The record notes several categories or time points for the primary outcome and lists a secondary cognition outcome. When more than one result can be examined, readers need to know which contrast was primary and how other analyses were handled. The registry does not report that strategy. This does not show that the protocol lacked one; it means the record does not document it.

The safety entries provide a further lesson in cautious reading. Counts can be described directly, but they do not identify causality or provide a complete picture of risk. Taken together, the trial record demonstrates why transparent reporting of estimates, uncertainty, analysis populations, and outcome-selection rules is needed alongside concise design summaries.

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 important limitation for statistical interpretation is the absence of a single numerical primary-outcome comparison in the registry information. The record says the primary outcome includes several categories or time points and is not reduced to one comparison. Without a reported estimate and uncertainty measure, the primary contrast’s direction, magnitude, and precision cannot be assessed.

The record does not report the specific cannabidiol dose, detailed eligibility criteria, baseline outcome values, adherence, or the operational procedures used to maintain masking. It identifies a six-week study and stable antipsychotic medication, but does not give enough detail to evaluate variation in treatment exposure or the full clinical context of the participants.

Statistical-plan details are also limited. The registry record does not report the sample-size justification, the primary analysis model, the analysis population, missing-data methods, multiplicity handling, or whether interim analyses were planned or conducted. It also does not give the numerical outcome data needed to evaluate distributions, variability, or the effect of any missing observations. These omissions constrain assessment of both the analysis and its precision.

The safety information is similarly bounded: the entries give participant counts for serious and other adverse events, but do not report event descriptions, severity, relatedness, or deaths. The reported group counts and event counts should be read as registry entries rather than as a complete account of trial follow-up. These limitations concern what is documented in the registry record; they do not establish what was or was not included in other trial materials.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Cannabidiol Treatment of Cognitive Dysfunction in Schizophrenia — NCT00588731.
• Registry record last updated 2017-06-08; status last verified 2017-06.
• Results first posted 2017-06-08.
• 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

The registry describes a completed Phase 2, randomized, quadruple-masked, parallel-group trial sponsored by Yale University. It compared cannabidiol with placebo added to stable antipsychotic medication in people with schizophrenia or schizoaffective disorder. Enrollment was 41, and the study was described as six weeks in duration.

The primary endpoint was verbal short term memory at 6 weeks, measured as a t-score using the Hopkins Verbal Learning Test; higher scores represent better verbal learning. Overall cognition measured on the MATRICS Battery was listed as a secondary outcome. The registry does not provide a single numerical comparison for the primary outcome. Safety entries report zero serious adverse events in each group and other adverse events in both groups; deaths are not reported in the registry record.