Neural Substrates in Nicotine Withdrawal: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Neural Substrates in Nicotine Withdrawal (NCT01001520), a randomized phase 2 study. The primary outcome is Measure of Brain Activity: Blood Oxygen Level Dependent (BOLD) fMRI Signal Change During the "N-back" Working Memory Task (Brain Region: Right Dorsolateral Prefrontal Cortex; Right DLPFC).

2. Clinical Question

3. Trial Design

NCT01001520, titled Neural Substrates in Nicotine Withdrawal, is recorded as a Phase 2 randomized, double-masked crossover study sponsored by the University of Pennsylvania. The registry record lists an enrollment of 218 and a completed status. The recorded study start is 2010-01 and primary completion is 2012-10. These overall enrollment figures should be distinguished from the smaller numbers in the posted outcome summaries: the primary outcome description says 29 subjects completed both fMRI sessions, with data from 9 excluded, while the arm summaries report 20 participants per condition.

In a crossover design, each participant receives multiple study conditions, so a participant can contribute observations under both the active medication and comparator. This can make within-person contrasts informative because each participant serves as their own comparison. The primary outcome description explicitly says that the brain signal change was analyzed within subjects. However, the registry record does not report the treatment sequence, allocation ratio, washout procedures, or the modeling details used to account for period or sequence effects. Those details should not be inferred from the crossover label alone.

Each participant completed two 11-day medication periods, one with tolcapone and one with placebo. The fMRI assessments were scheduled on Day 8 of each period, and the primary outcome timeframe is listed as fMRI scan sessions on Days 8 and 29. The task varied working-memory demands across 0-back, 1-back, 2-back, and 3-back conditions, with brief rest periods between conditions. The main registry outcome is a continuous measure, reported as a mean with standard error.

The registry record lists cognitive accuracy, reaction time, smoking behavior, cigarette craving, and withdrawal symptoms as secondary outcome areas. It does not report the planned sample-size justification, the full statistical analysis plan, or whether interim analyses were conducted. The enrollment figure alone does not establish how many participants were expected to contribute to each particular endpoint.

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: 2670 subjects completed initial screening over the phone; 669 (25%) were eligible. Of these, 418 (62%) scheduled an in-person screening visit; 218 (50%) attended this visit. 73 (17%) provided blood samples to determine final eligibility, based on genetic \& liver function tests. 54 (74%) reached final eligibility; 46 (85%) started study medication.

Medication Period 1

Reasons for not completing this period:

Washout Period

Reasons for not completing this period:

Medication Period 2

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: 29 subjects completed both fMRI scan sessions; however, data from 9 subjects were excluded from analysis, due to either poor fMRI data quality, low task accuracy (defined as task scores falling two standard deviations below the mean), or a failure to respond to more than 30% of the task's items. Below, we report on the 20 remaining subjects.

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: Measurements were taken during their first study visit, the medical screening visit.

6. Primary Endpoint

The registry lists the primary outcome as Measure of Brain Activity: Blood Oxygen Level Dependent (BOLD) fMRI Signal Change During the "N-back" Working Memory Task (Brain Region: Right Dorsolateral Prefrontal Cortex; Right DLPFC), measured over At fMRI scan sessions - Days 8 and 29.

The primary endpoint is the mean BOLD fMRI signal change in the right dorsolateral prefrontal cortex during the N-back working-memory task. BOLD is a signal derived from fMRI that reflects changes in blood oxygenation associated with brain activity. For this outcome, the study calculated the signal during each task condition relative to the rest periods. The description specifies a within-subject analysis and reports the measure in BOLD signal units.

The N-back task presents geometric figures and asks participants to respond when a target repeats after a specified number of intervening figures. The registry record describes four conditions, from 0-back through 3-back, which impose increasing memory demands. Measuring brain signal while participants perform a defined task provides a way to examine neural activity associated with working memory, rather than relying only on a subjective report or a behavioral score.

The scans were conducted on Day 8 of each medication period after at least 24 hours of smoking abstinence. That timing places the assessment within the study's intended nicotine-withdrawal context. The endpoint therefore concerns a task-related brain signal under the recorded study conditions; it is not itself a direct measure of withdrawal symptoms, everyday cognitive functioning, or a clinical outcome.

The posted mean is 0.27 for both placebo and tolcapone. That equality of rounded arm means does not establish that the underlying effects are identical, nor does it demonstrate equivalence. Interpretation also depends on the uncertainty around the comparison and on the analysis method, particularly because the study description identifies a within-subject analysis.

7. Results Posted in the Registry

• Tolcapone: mean 0.27 versus 0.27 on control; difference 0.00 (95% CI -0.10 to 0.10), standardized effect d = 0.00; z-test p = 1.000.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Cognitive Performance: Accuracy

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard errors.
• Result:
  • Tolcapone: mean 51.80 versus 49.90 on control; difference 1.90 (95% CI -1.17 to 4.97), standardized effect d = 0.38; z-test p = 0.225.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Tolcapone and the control. The interval gives the range of effects that remain compatible with the data.

Cognitive Performance: Reaction Time

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard errors.
• Result:
  • Tolcapone: mean 520.00 versus 518.00 on control; difference 2.00 (95% CI -42.35 to 46.35), standardized effect d = 0.03; z-test p = 0.930.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Tolcapone and the control. The interval gives the range of effects that remain compatible with the data.

Subjective Symptoms: Smoking Behavior

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Tolcapone: mean 14.30 versus 14.20 on control; difference 0.10 (95% CI -2.35 to 2.55), standardized effect d = 0.03; z-test p = 0.936.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Tolcapone and the control. The interval gives the range of effects that remain compatible with the data.

The registry names several secondary domains, including cognitive task performance and subjective smoking-related measures. The detailed numerical results available for comparison cover cognitive accuracy, reaction time, and average daily cigarette consumption. Across those outcomes, the recalculated estimates are not statistically distinguishable from zero at conventional levels, while the sponsor-reported regression p-values differ for some outcomes. This pattern does not provide a consistent, definitive secondary signal that changes the interpretation of the primary BOLD result.

The secondary outcomes address related but distinct questions. Behavioral accuracy and reaction time measure task performance, whereas cigarette consumption is a self-reported or recorded behavior measure. Neither is a direct substitute for task-related BOLD signal in the right dorsolateral prefrontal cortex. Similarity or difference across these measures would not, by itself, confirm or contradict the neural endpoint. The registry record lists craving and withdrawal symptoms, but their numerical results are not reported in the detailed results available for interpretation.

Secondary comparisons generally carry less weight than a prespecified primary endpoint because they may be numerous and may be examined across multiple measures or time points. When many hypotheses are tested, the chance of at least one apparently notable result can increase. Whether the trial adjusted for multiple comparisons, designated a hierarchy, or treated any secondary results as confirmatory is not reported in the registry record. Accordingly, unadjusted secondary p-values should be read as exploratory evidence rather than standalone proof.

The qualitative pattern is best understood as a collection of uncertain, outcome-specific estimates. It should not be converted into a broad conclusion about all cognitive or subjective effects. The limited analysis set and the absence of a reported multiplicity plan also constrain how strongly secondary findings can support or challenge the primary comparison.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Cognitive Performance: Accuracy
• Cognitive Performance: Reaction Time
• Subjective Symptoms: Smoking Behavior
• Subjective Symptoms: Cigarette Craving
• Subjective Symptoms: Withdrawal Symptoms

9. Statistical Interpretation

10. Statistical Methods Explained

The primary outcome is continuous and summarized as a mean with standard error. A mean describes the center of the observed values, while the standard error describes the uncertainty in an estimated mean. Standard error is not the same as the spread of individual participants' measurements: it is intended to express how precisely the mean has been estimated. The posted primary standard errors are 0.04 for placebo and 0.03 for tolcapone.

What does the mean difference represent?

The mean difference compares the two condition means, with tolcapone contrasted against placebo in the recalculation. The recalculated difference is 0.0 because the posted means are both 0.27. A difference of zero in rounded summaries means the displayed means coincide; it does not prove that individual paired observations are identical or that the true treatment contrast is exactly zero.

The recalculated confidence interval runs from -0.098 to 0.098. A confidence interval is a measure of statistical uncertainty around an estimate, constructed under a specified analysis framework. It is not a guarantee that the true value lies in the interval, nor does it describe the range of individual participant outcomes. Whether an interval is narrow enough to rule out a meaningful effect depends on the scientific context and a prespecified threshold. No such threshold is reported in the registry record.

Why does the crossover design matter?

In a crossover trial, treatment comparisons can use the fact that the same person receives both conditions. Within-person analysis accounts for how each participant's measurements relate across conditions, and can be more informative than treating all condition observations as unrelated. The primary outcome description explicitly identifies a within-subject analysis. The simple recalculation uses posted summary information and does not reconstruct the paired participant-level model. The within-person covariance, treatment sequence, period effects, and any carryover assessment are not reported in the registry record. Without those details, the recalculation and sponsor's regression result should not be assumed to use identical methods.

The sponsor analysis is described as linear regression and reports p = 0.88. A p-value measures how compatible the observed data are with a specified null hypothesis under the assumptions of the analysis. It is not the probability that the null hypothesis is true, and it does not quantify the size or practical importance of a treatment effect. The simple unadjusted recalculation reports p = 1.0. Differences between the two p-values can arise because the analyses may use different models or information; the registry record does not supply enough detail to identify the reason. The sponsor's analysis is the analysis reported by the trial, while the recalculation is a separate summary-statistic comparison.

What can standard errors and dispersion tell us?

For a continuous outcome, variability among participants and uncertainty in a mean are related but distinct. Standard deviation describes variation among observations; standard error describes uncertainty in an estimated mean. The primary endpoint and the cognitive outcomes are reported with standard errors. The smoking-behavior outcome is reported with standard deviations. These measures should not be compared as if they represented the same quantity. For the primary outcome, the recalculation also reports a pooled standard deviation of 0.158 as a scale for the between-condition contrast; it is not a substitute for the paired-model uncertainty.

Over-dispersion is a general concern when observed variability exceeds what a statistical model assumes. A model that understates variability can produce confidence intervals that are too narrow and p-values that appear more decisive than warranted. The registry record does not report a dispersion assessment for the primary endpoint, so no claim about over-dispersion in this trial can be made. More generally, model assumptions should be considered alongside the reported point estimate and uncertainty.

How should the planning illustrations be read?

The planning illustrations for selected secondary outcomes use the observed effect as a starting point and show participant counts for detecting stated fractions of that effect under a two-sided significance level of 0.05, equal allocation, and a normal approximation. For example, the rows describe planning for 100%, 75%, or 50% of the observed effect. These are hypothetical design illustrations, not the trial's planned sample-size justification and not observed power. The registry record does not report that these assumptions were used to plan this trial. The illustrations are especially sensitive to the observed effect: when a small observed difference is used as the target, the implied participant counts can be very large. They should not be interpreted as evidence that a future study will achieve a particular result.

For planning, participants per arm for 80% power and participants per arm for 90% power are presented for some secondary measures. Those calculations are not reported for the primary endpoint in the available record. The counts are planning quantities, not observed participants, and they do not change the uncertainty in the completed trial's estimates.

Overall, the most defensible reading separates three elements: the posted arm means, the uncertainty in the recalculated contrast, and the sponsor's model-based test. None alone establishes equivalence. The crossover structure and the absence of participant-level data mean the recalculation is best treated as a transparent, unadjusted reference rather than a replacement for the trial's own analysis.

11. Confidence Intervals and Precision

The primary comparison is centered at a recalculated mean difference of 0.0. Its 95% confidence interval extends from -0.098 to 0.098. This interval includes zero, so the recalculation does not distinguish a positive from a negative contrast at the stated confidence level. It also leaves uncertainty around the size of any difference; the interval's endpoints are not evidence that effects at those exact values occurred.

Precision is not the same as whether a result is statistically significant. A confidence interval helps show the range of estimates compatible with the data and analysis assumptions, whereas a p-value summarizes compatibility with a null hypothesis. The interval should be judged against a threshold for a meaningful BOLD signal difference, but such a threshold is not reported in the registry record. Without that context, it is not possible to conclude that the interval is sufficiently narrow to rule out an important effect.

The recalculation is derived from the posted summary statistics and is unadjusted. The primary analysis is described as within-subject, but the paired covariance and full regression specification are not reported in the registry record. The interval therefore does not reproduce the uncertainty from the sponsor's participant-level analysis. The sponsor's reported p-value is 0.88, but a confidence interval for that analysis is not reported in the registry record.

As a general statistical point, confidence intervals depend on the model and assumptions used to calculate them. A different analysis that accounts for the crossover pairing, period, or sequence could yield different uncertainty. The available record does not permit those model details to be checked. The interval is useful as a summary-statistic-based indication of precision, with that methodological limitation kept in view.

12. Analyses Reported by the Sponsor

The registry reports a linear regression analysis for the primary comparison, with p = 0.88. It does not provide a sponsor-analysis estimate, confidence interval, or further specification of the regression model. The posted means are 0.27 for both placebo and tolcapone, and the simple unadjusted recalculation gives a mean difference of 0.0, a 95% confidence interval from -0.098 to 0.098, and p = 1.0.

The recalculation is not a reproduction of the sponsor's regression. It uses posted summary statistics and does not have participant-level observations or the paired covariance needed to reconstruct the stated within-subject analysis. The registry record does not say whether the regression included terms for period, sequence, or other covariates, so the reason for the different p-values cannot be identified from the record.

The two results are directionally consistent in the limited sense that neither reports strong statistical evidence of a difference. They are not interchangeable: the sponsor's p-value belongs to the reported regression, while the recalculated estimate and interval describe a separate unadjusted summary-statistic comparison. The registry record reports no discrepancy between these analyses. Neither result establishes equivalence or proves the absence of a treatment effect.

13. Multiplicity, Missing Data and Analysis Populations

The registry lists multiple outcome measures and secondary outcome domains. Testing several outcomes can increase the chance of observing a small p-value by chance, even when no real differences exist. Statistical approaches such as adjustment for multiple comparisons, prespecified testing hierarchies, or labeling secondary analyses as exploratory can address this issue. Whether any such approach was used is not reported in the registry record. The reported secondary p-values therefore should not be treated as multiplicity-adjusted unless the record says so; no adjustment is described.

The record also does not report whether an interim analysis was planned or conducted, or whether stopping criteria were specified. These details cannot be inferred from the completed status. The full analysis plan, including the intended covariates, treatment-sequence handling, and any subgroup analyses, is not reported in the registry record. The study summary raises a genetic-background question, but genetic subgroup estimates and their analysis plan are not reported.

Some information about exclusions is available for the primary fMRI outcome. The description says 29 subjects completed both scans and data from 9 were excluded because of poor fMRI data quality, low task accuracy, or failure to respond to more than 30% of task items. It also defines low task accuracy as task scores falling two standard deviations below the mean. The criteria are described, but the number excluded for each reason, the timing of those decisions, and whether the criteria were prespecified are not reported in the registry record.

The overall enrollment is 218, while the primary scan description and arm summaries concern a smaller analysis set. The record does not explain all transitions from enrollment to each endpoint's analysis population. It does not report an intention-to-treat definition, missing-data imputation method, sensitivity analyses, or how participants with incomplete outcome data were handled. These omissions limit assessment of whether exclusions or missing observations could have influenced the estimates.

These are reporting limitations rather than evidence that a particular procedure was or was not used. The appropriate conclusion is that multiplicity handling, missing-data methods, and several analysis-population details are not reported in the registry record.

14. 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 adverse-event record lists no participants with serious adverse events in either group: 0 among 38 at risk for placebo and 0 among 40 at risk for tolcapone. For other adverse events, the record likewise lists 0 among 38 at risk for placebo and 0 among 40 at risk for tolcapone. These figures describe the recorded event counts and the corresponding numbers at risk.

Zero recorded events in these groups should not be read as proof that no adverse events occurred among all enrolled participants or that the treatments have no safety risks. The adverse-event denominators differ from the outcome-summary counts, and the registry record does not explain the relationship between these sets of participants. It also does not provide a list of serious-event terms, because no serious terms are listed.

Deaths are not reported in the registry record. The adverse-event figures are descriptive and do not establish a comparative safety profile. They should be interpreted within the recorded groups and follow-up information, which is not fully detailed in the registry record.

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

The primary result describes BOLD fMRI signal change during a specific working-memory task in the right dorsolateral prefrontal cortex, measured during the study's medication periods and after at least 24 hours of smoking abstinence. The posted condition means are both 0.27. The recalculated comparison is centered at zero, and its interval includes differences in either direction. The sponsor's regression reports p = 0.88. Taken together, these data do not establish a clear difference between the conditions for this endpoint in the analyzed participants.

That finding is not the same as demonstrating that tolcapone and placebo have identical effects. A non-significant test does not prove no effect, and an equivalence conclusion requires a prespecified margin and an analysis designed to assess equivalence. No equivalence margin is reported in the registry record. The uncertainty interval also needs to be considered in relation to a meaningful signal threshold, which is not reported.

The result does not establish effects on all aspects of cognition, smoking behavior, craving, withdrawal symptoms, or long-term outcomes. The primary endpoint is a neural measure during a laboratory task, not a direct measure of daily functioning or a clinical endpoint. Secondary measures must be assessed on their own terms, and multiplicity and analysis details are not reported.

The record describes a selected fMRI analysis set after exclusions, and does not fully explain how that set relates to the total enrollment. The summary-statistic recalculation also differs in method from the stated within-subject analysis. These limits mean the numerical results should be interpreted as evidence about the posted analysis, not as a complete account of every participant or every possible effect.

In general, a trial result is conditional on its population, procedures, outcomes, and analysis methods. The registry record supports a cautious description of the measured comparison; it does not support a broad claim about benefit, lack of benefit, or safety beyond the reported data.

16. Why This Trial Matters Statistically

This trial is statistically interesting because the primary endpoint is a neural signal measured in a randomized crossover design. Crossover studies can make efficient use of within-person comparisons, but their interpretation depends on how repeated observations are modeled and on factors such as treatment sequence and period. The record identifies a within-subject analysis, making the distinction between paired and unpaired summaries especially relevant.

The posted arm summaries allow a transparent unadjusted recalculation, but they do not contain the participant-level information needed to reproduce the crossover analysis. The sponsor's linear-regression p-value and the recalculated summary-statistic result are therefore different views of the data, not competing estimates obtained under demonstrably identical assumptions. This illustrates why effect estimates, uncertainty, and model description matter alongside a p-value.

The study also illustrates the difference between absence of strong evidence for a difference and evidence of equivalence. The recalculated interval includes zero, but no equivalence margin is reported. Without a meaningful-effect threshold, the practical interpretation of the interval remains limited. The record's exclusions and the distinction between overall enrollment and the smaller fMRI analysis set further show why analysis populations should be described clearly.

Finally, the range of secondary measures creates a multiplicity question. Cognitive, behavioral, and subjective outcomes can complement a neural endpoint, but they address different constructs and should not be pooled into a single broad conclusion. The registry record does not report multiplicity procedures or complete results for all listed subjective outcomes. Careful separation of primary evidence, exploratory secondary findings, and missing analysis details is central to a sound statistical reading.

17. 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 is based on fMRI data from a subset of the enrolled participants. The record reports 29 subjects completing both scans and 9 exclusions, with reasons related to data quality, task accuracy, or task response. It does not report the count for each reason or give a complete participant flow for the primary analysis. The posted arm summaries use 20 participants per condition, but the relationship among these counts and the overall enrollment of 218 is not fully explained.

The primary endpoint description says the analysis was within-subject, but the record does not provide the paired data, covariance, complete model specification, or confidence interval for the sponsor's regression. The recalculated comparison uses posted summary statistics and cannot reproduce those features. Treatment order, washout procedures, period effects, and carryover assessment are not reported in the registry record, although they can matter to interpretation of crossover data.

The registry record does not report a sample-size justification for the primary endpoint, a multiplicity strategy, missing-data methods, or a detailed analysis-population definition. Although the study summary mentions possible variation by genetic background, subgroup results are not reported. Numerical results for some listed subjective outcomes are also not included among the detailed secondary results available for interpretation.

The endpoint itself is a task-related BOLD signal in a specified brain region, measured under study conditions. It does not directly represent clinical symptoms or everyday cognitive functioning. A threshold for a meaningful signal difference is not reported, limiting interpretation of the confidence interval in practical terms. These limitations do not determine the direction of the result; they describe what the registry record does not allow readers to assess.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Neural Substrates in Nicotine Withdrawal — NCT01001520.
• Registry record last updated 2014-07-02; status last verified 2014-05.
• Results first posted 2014-07-02.
• 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.

21. Record Summary

NCT01001520 is a completed Phase 2 randomized, double-masked crossover study sponsored by the University of Pennsylvania. The recorded enrollment is 218; the study start is 2010-01 and primary completion is 2012-10. Participants completed an 11-day tolcapone period and an 11-day placebo period, with fMRI scans scheduled on Day 8 of each period after at least 24 hours of smoking abstinence.

The primary outcome was mean BOLD signal change in the right dorsolateral prefrontal cortex during the N-back task. The posted means are 0.27 in both conditions. The unadjusted recalculation gives a mean difference of 0.0, a 95% confidence interval from -0.098 to 0.098, and p = 1.0; the sponsor's linear-regression analysis reports p = 0.88. The registry record describes exclusions from the fMRI analysis and lists secondary cognitive and subjective outcomes, but does not report several analysis-plan, missing-data, and multiplicity details.