An Eval of Neurocognitive Function, Oxidative Damage, and Their Association With Outcomes in METH and Cocaine Abusers.: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for An Eval of Neurocognitive Function, Oxidative Damage, and Their Association With Outcomes in METH and Cocaine Abusers. (NCT00628927), a registered phase not stated study. The primary outcome is Stroop Color-word Task.

2. Clinical Question

The primary objective is framed around a relationship between a cognitive task and treatment completion, not around assignment to different treatments. The study description says that participants in the dependent group would be analyzed according to whether they completed treatment as defined by the study. That definition is not reported in the registry record.

The record also identifies two secondary measures: the Barrett Impulsiveness Scale Version 11 (BIS-11) and tail length from the Comet Assay for oxidative damage. These measures indicate that the research addressed impulsiveness and cellular damage in addition to Stroop performance. Their results and their specific role in analyses are not reported in the registry record.

3. Trial Design

The registry lists this as a completed study sponsored by the University of Cincinnati, with enrollment of 217. The recorded start is 2008-02 and the primary completion is 2009-10. The record describes a study of neurocognitive function, oxidative damage, and their association with treatment outcomes in methamphetamine and cocaine abusers.

The record describes two groups. The methamphetamine and/or cocaine dependent group was seeking treatment and was also enrolled in CTN0031 (NCT00573183). The group was to be analyzed according to treatment completion as defined by the study. The second group consisted of normal controls recruited from the community. These groups do not form a like-for-like control comparison, and the registry does not state that participants were randomized. Allocation is not stated.

The study description includes more than a single treatment-completion question. It identifies an objective concerning whether neurocognitive performance predicts treatment outcomes and another concerning risk and actual damage to DNA and other cell parts. The listed outcomes include the Stroop Color-word Task, BIS-11, and Comet Assay tail length. The record gives a single study visit as the timeframe for the primary measure.

The registry does not report the full protocol, recruitment procedures beyond the community-control description, eligibility criteria, treatment details, or the operational definition of treatment completion. It also does not report a detailed statistical analysis plan or a sample-size justification. Those omissions limit what can be concluded about how the study was conducted and how its intended analyses were specified.

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: 6 stimulant abusers met at least one exclusion criterion, 3 for a history of stroke and 3 for a history of seizures. 2 of those 6 were incorrectly enrolled into the study. The most common exclusion criteria met by the normal control screeners was having a DSM-IV substance use diagnosis and positive urine toxicology screen.

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: Stimulant dependent participants were starting treatment, and participating in the CTN0031 study. Normal controls were recruited from the community.

6. Primary Endpoint

The registry lists the primary outcome as Stroop Color-word Task, measured over Single study visit.

The primary endpoint is the mean score on the Stroop Color-word Task, measured in seconds, with standard deviation as the stated measure of dispersion. The task requires a participant to name the ink color of a printed word while inhibiting the learned tendency to read the word. For example, the word “red” might be printed in blue ink.

The registry describes three trials. Errors are subtracted from the reaction time for each trial to form three summary scores. The derived interference score is obtained by subtracting the reaction time for the first trial from the reaction time for the third trial. The endpoint is therefore based on performance under a task that requires both rapid responding and inhibition of a competing response.

The measure was selected to address the study’s stated prediction question: whether Stroop performance is associated with treatment completion. The registry says the objective was to replicate a reported finding in participants with cocaine use disorders and extend the question to participants with methamphetamine use disorders. This rationale describes why the measure was of interest; it does not establish that a predictive association was observed in this study.

The registry gives a single study visit as the timeframe but does not report the mean scores, standard deviations, group-specific estimates, or an association between Stroop performance and completion. Those outcome results are not reported in the registry record, so the size and precision of any relationship cannot be assessed from the available results.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies a continuous primary measure summarized as a mean with standard deviation. It also describes the derivation of a Stroop interference score and the intended use of neurocognitive performance in relation to treatment completion. The specific statistical analyses used to answer that question are not reported in the registry record. The explanations below are general statistical context, not claims about analyses that were performed.

What does a mean and standard deviation describe?

General explanation: a mean gives a center for a set of measurements. A standard deviation describes how dispersed individual measurements are around that center. Reporting both can help readers understand a continuous measure’s typical level and its variability. A mean and standard deviation do not, on their own, show whether groups differ, whether a measure predicts an outcome, or how precise an estimated difference is.

For the Stroop task, the registry specifies seconds as the unit and describes a mean as the summary parameter. The endpoint procedure uses reaction times adjusted for errors, then derives an interference score from trial summaries. Results for the mean or dispersion are not reported in the registry record. It is therefore not possible to assess the observed distribution, compare scores, or evaluate whether the measure behaved as intended in this study.

How would a prediction question be analyzed?

General explanation: prediction asks whether information from a measure is associated with a later or otherwise defined outcome. In this study description, the outcome of interest is treatment completion, and Stroop performance is the proposed predictor. An analysis would need a clear definition of completion and a specified model or comparison. The registry says completion was defined by the study, but does not provide that definition or report the model used.

A predictive association is not automatically evidence that the cognitive measure causes completion. Other participant characteristics or features of treatment may be related to both performance and completion. A sound interpretation depends on the study design, measured variables, analytic choices, and the uncertainty around the estimated relationship. The available record does not report enough analysis detail to assess those matters.

What would uncertainty statistics add?

General explanation: a confidence interval communicates a range of values compatible with the data and the stated statistical model, at the interval’s chosen confidence level. Its width reflects precision: a narrower interval generally indicates greater precision than a wider interval. A p-value addresses compatibility with a specified null hypothesis under model assumptions; it does not measure the size or importance of an effect. No confidence interval or p-value for the study’s primary outcome is reported in the registry record.

When a study reports only a point estimate, readers have limited information about how stable that estimate may be. When no estimate is reported, as for the primary Stroop outcome in this record, readers cannot assess either the pattern or its precision. This is why the study objective cannot be treated as an empirical result.

Why can dispersion matter?

General explanation: variability among individual observations affects how precisely a group mean or an association can be estimated. Greater dispersion can make an estimate less precise when the amount of information is otherwise similar. It can also matter when a statistical model assumes a particular distribution or a particular relationship between the mean and variance. The standard deviation is the registry’s stated dispersion measure, but no observed value is reported.

For count outcomes, over-dispersion means that the observed variability exceeds what a model assumes. It can make standard errors too small if ignored. This is a general issue for count-data methods, not a reported feature of the continuous Stroop endpoint or a claim about an analysis in this study. The registry does not report enough information to assess whether over-dispersion was relevant to any outcome analysis.

How should the planning illustrations be understood?

General explanation: sample-size planning asks how much information a proposed study might need to detect a specified effect under stated assumptions. A planning calculation is conditional on those assumptions; it is not a measure of what the completed study actually achieved. In particular, a sample-size illustration based on an observed effect is not observed power.

The registry’s stated illustration assumptions specify a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The target effect is described as a fraction of the observed effect. For outcomes other than time-to-event outcomes, the convention is participants per arm; for time-to-event outcomes, it is total events under the Schoenfeld approach. These are conventions for interpreting planning illustrations, not evidence that the study used those design assumptions. The registry does not report its own sample-size justification or statistical design rationale.

Because numerical planning values and the underlying observed effect are not reported in the registry entries, no particular planning requirement can be interpreted. Any such calculation would remain illustrative and dependent on its assumptions, rather than a reconstruction of the study’s original design.

What can the registry’s analysis listing establish?

The record lists 0 analyses. This describes what is listed in the registry record; it does not establish that investigators conducted no analyses outside the registry. Without posted analysis results, readers cannot verify which participants were included, how missing observations were handled, what model was fitted, or whether the analysis followed a prespecified plan. The statistical methods used for the study are not reported in the registry record.

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("Stimulant Dependent Completers", "Stimulant Dependent Treatment Non-Completers")
n   <- c(130, 51)
m   <- c(55.4, 50.5)
sp  <- c(22.9, 21)
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  Stimulant Dependent Completers  130  55.400  22.900  51.426  59.374
CARM  Stimulant Dependent Treatment Non-Completers  51  50.500  21.000  44.594  56.406

11. Multiplicity, Missing Data and Analysis Populations

The record lists a primary Stroop endpoint and two secondary outcomes: the Barrett Impulsiveness Scale Version 11 and Comet Assay tail length. It does not report the analysis plan, the number of hypotheses tested, or any adjustment for multiple comparisons. It is therefore not possible to determine how multiplicity was handled or whether any particular result was designated as confirmatory.

General explanation: when several outcomes or comparisons are examined, the chance of obtaining at least one apparently unusual result can increase. Prespecifying a primary question and an approach to multiple testing helps readers distinguish confirmatory analyses from exploratory ones. The registry identifies a primary objective and secondary outcomes, but it does not provide enough information to establish how these distinctions were implemented in the analysis.

Missing-data methods are not reported in the registry record. The enrollment count does not show how many participants had usable Stroop measurements, completed all task trials, or contributed to each secondary outcome. There is no reported account of missing observations, exclusions, or sensitivity analyses addressing missingness. Therefore the extent and possible influence of missing data cannot be assessed.

The analysis populations are also not reported. Although the dependent group was to be analyzed by treatment completion, the record does not state the criteria used to define completion or which participants were included in each analysis. It does not report whether all enrolled participants, only participants with available measurements, or another group formed the analysis population. These uncertainties limit the reproducibility and interpretation of any result, and no outcome estimates are listed to resolve them.

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.

The registry lists serious and other adverse-event counts for two groups. For “Simulant Dependent Participants,” 175 participants were at risk for serious events and 0 were recorded as affected; 175 were at risk for other events and 0 were recorded as affected. For “Normal Control Participants,” 30 were at risk for serious events and 0 were recorded as affected; 30 were at risk for other events and 0 were recorded as affected.

These entries mean that the registry reports no affected participants in the listed serious-event and other-event categories. They do not establish that no symptoms or events of any kind occurred, because the record’s listed counts concern these adverse-event categories. The deaths values are not reported in the registry record. The record lists no top serious-event terms.

The at-risk counts are safety denominators, not outcome-analysis sample sizes. They should not be used to infer how many participants contributed to the Stroop, BIS-11, or Comet Assay analyses. The registry does not provide detailed event definitions or an account of how safety information was collected. These safety figures also do not answer whether Stroop performance was associated with treatment completion or whether oxidative-damage measures differed between groups.

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

The study addresses a clinically relevant statistical question: whether performance on a neurocognitive task is associated with treatment completion among people with stimulant dependence, and whether a prior finding described for cocaine use disorders extends to methamphetamine use disorders. It also frames a comparison of cellular damage between people with and without substance abuse disorders. These are the questions the study set out to examine, not reported conclusions.

The registry provides the primary measure’s name, unit, summary type, timeframe, and scoring description. It also identifies the study groups and two secondary measures. However, it does not report the Stroop means or standard deviations, the relationship with treatment completion, or the oxidative-damage and impulsiveness results. Without those estimates, their precision, direction, and magnitude cannot be described.

Accordingly, the record does not establish that Stroop performance predicted treatment completion, nor does it establish the presence or absence of group differences in oxidative damage. It also does not provide evidence that any measured characteristic caused treatment completion. An association, if reported, would need to be interpreted in light of the study design and potential alternative explanations.

The completed status and enrollment of 217 describe study administration and enrollment, not the success of an analysis. The registry’s absence of listed analyses likewise should not be interpreted as proof that no analysis took place; it means that analyses are not listed in the record. The most defensible reading is that the study’s aims and measurement approach are documented, while its principal statistical findings are not reported in the registry record.

14. Why This Trial Matters Statistically

This study is statistically interesting because it links a performance measure from a cognitive task with a defined treatment outcome. The Stroop task is described as requiring participants to name ink colors while inhibiting word reading, and its derived interference score is based on reaction-time summaries across trials. That operational detail makes clear what kind of performance the investigators intended to relate to treatment completion.

The question is also extended across people with cocaine use disorders and methamphetamine use disorders, while the broader study description includes community controls and an oxidative-damage objective. The record therefore brings together prediction, group comparison, and more than one type of outcome. Distinguishing these aims matters: a cognitive measure’s association with completion is not the same estimand as a difference in oxidative damage between groups.

Statistically, the study also illustrates why a clearly stated objective is not a substitute for reported estimates. Readers need results and uncertainty measures to judge whether an association is large or small, precise or imprecise, and consistent with the research question. Here, the registry documents the aims and measures but does not report the primary results or analyses. The evidence cannot be appraised from the stated objectives alone.

The group structure further matters to interpretation. The dependent participants were seeking treatment and were also enrolled in CTN0031 (NCT00573183), whereas normal controls were recruited from the community. The registry explicitly does not characterize this as a like-for-like control comparison. That design context cautions against treating group contrasts as if they arose from randomized assignment or from otherwise equivalent groups.

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 main limitation for interpreting this study is that the registry record does not report the primary outcome results or analyses. There are no reported Stroop summary values, estimates relating performance to treatment completion, confidence intervals, or test results. The listed secondary outcomes also have no reported results. As a result, the research questions cannot be evaluated statistically from the posted information.

The record does not report the definition of treatment completion, despite describing analysis by completion status. It does not state the analysis population, the handling of missing data, the model used, or whether relevant participant characteristics were accounted for. These omissions prevent assessment of how the proposed predictive relationship was estimated and how sensitive it may be to analytic choices.

The study groups are not a like-for-like control comparison, and allocation is not stated. The dependent participants were seeking treatment and had also enrolled in CTN0031 (NCT00573183); community controls were recruited as normal controls. The record does not provide enough detail to assess comparability between groups or the implications of recruitment and treatment context for any group contrast.

The description names a single study visit for the primary endpoint, but does not report the measurement procedures beyond the task scoring description. It does not provide the full protocol, detailed eligibility criteria, or a sample-size justification. The planning convention in the registry is not a substitute for the study’s own design rationale. Finally, the safety record does not report deaths, and the available adverse-event counts do not resolve questions about the study’s primary cognitive or oxidative-damage outcomes.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: An Eval of Neurocognitive Function, Oxidative Damage, and Their Association With Outcomes in METH and Cocaine Abusers. — NCT00628927.
• Registry record last updated 2015-12-30; status last verified 2015-12.
• Results first posted 2013-08-30.
• 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

This completed study, sponsored by the University of Cincinnati, enrolled 217 participants. The registry records a start of 2008-02 and primary completion of 2009-10. Its aims concerned neurocognitive performance and treatment completion, and comparison of DNA and other cellular damage in people with and without substance abuse disorders.

The primary measure was the Stroop Color-word Task, reported as a mean in seconds with standard deviation and assessed at a single study visit. Secondary outcomes were the BIS-11 and Comet Assay tail length. The dependent group was seeking treatment and was also enrolled in CTN0031 (NCT00573183); community controls were recruited as normal controls. The groups were not a like-for-like control comparison, and allocation was not stated.

The registry lists 0 analyses and does not report primary or secondary outcome results. Serious and other affected-participant counts are 0 in both listed groups; deaths are not reported in the registry record. The statistical findings and the study’s detailed analysis methods therefore remain unavailable in the record.