Motivated Behavior in Adults With and Without ADHD: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Motivated Behavior in Adults With and Without ADHD (NCT02630017), a non-randomized phase 2 study. The primary outcome is Number of High-effort Selections in the Effort-based Decision Making Task.

2. Clinical Question

The task asks participants to choose between options requiring different amounts of physical effort for a small financial reward. The study’s stated aim was to investigate methylphenidate’s effects on motivated behavior in adults with and without ADHD. The endpoint records how often participants selected the high-effort option across the task trials. It is therefore a behavioral measure within an experimental task, rather than a clinical symptom score or a measure of everyday functioning.

The registry says the study was powered to compare the ADHD and non-ADHD groups, with treatment order counterbalanced within each group. However, numerical results needed to assess the primary question—including group means, standard errors, and a test of the comparison—are not reported in the registry record. The record also cautions that the clinical or physiological relevance of this basic science experiment is not established.

3. Trial Design

This completed phase 2 study was sponsored by the University of Arkansas. The registry lists an enrollment of 51 and a study start date of 2016-03-07, with primary completion on 2018-09-21. It identifies the allocation as non-randomized, the masking as double, and the model as crossover. These labels describe different features: allocation concerns assignment, masking concerns awareness of study conditions, and crossover describes the treatment structure. The record does not further explain the masking procedures or how non-randomized assignment was implemented.

The study included adults with ADHD and adults without ADHD. Within each group, the listed sequences were methylphenidate followed by placebo and placebo followed by methylphenidate. The registry describes order as counterbalanced, with approximately half of subjects within each group receiving drug first and half receiving placebo first. This sequencing is relevant because the endpoint compares the placebo and methylphenidate conditions. The record does not report details about the interval between sessions, washout procedures, adherence, or whether all enrolled participants completed both conditions.

A crossover design can make within-participant comparisons possible because a participant may contribute observations under more than one condition. Such comparisons can reduce the influence of stable differences between participants. They also require attention to order, period, and possible carryover effects. Whether and how those issues were assessed is not reported in the registry record.

The non-randomized allocation is an important qualification. Counterbalancing treatment order is not the same as random assignment, and the record explicitly indicates that the arms are not a like-for-like randomized control comparison. The registry does not provide a detailed statistical analysis plan, a sample-size justification, or results from an analysis of the endpoint. Consequently, the design description alone does not establish the size or precision of a treatment-condition difference.

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

Analysis population for the primary outcome, as defined in the registry: Approximately half of the subjects within each arm (ADHD or non-ADHD) received drug first and half received placebo first (i.e., order was counterbalanced). The study was powered to compare two groups (ADHD vs non-ADHD). Since order of drug was counterbalanced, this means all ADHD subjects were evaluated under both placebo and drug conditions, and this is also true for the non-ADHD 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.

6. Primary Endpoint

The registry lists the primary outcome as Number of High-effort Selections in the Effort-based Decision Making Task, measured over 1 hour post drug (or placebo) administration for each study session.

The primary endpoint is the number of high-effort selections in an effort-based decision-making task. The registry defines the measure as the number of such choices, summed across 50 trials. A high-effort choice requires 100 button presses with the non-dominant hand’s pinky finger; a low-effort choice requires 30 button presses with the dominant hand’s index finger. Each choice must be made within 15 seconds. The task offers a small financial reward and varies reward magnitude and probability.

The endpoint is intended to capture willingness to expend effort as the reward and its probability change. Counting high-effort choices turns task behavior into a continuous outcome that can be summarized by a mean and a measure of dispersion. The registry specifies the mean and standard error, with measurements taken 1 hour post drug or placebo administration for each study session. It describes the primary comparison as moving from the placebo condition to the methylphenidate condition.

This is a task-based behavioral endpoint, not by itself a direct measure of clinical benefit, symptoms, or functioning outside the experiment. The registry explicitly states that the clinical and/or physiological relevance of the results is not established. Although the endpoint definition and timing are reported, the observed means, standard errors, and treatment-condition estimates are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Statistical interpretation starts with identifying the outcome, the contrast, and the design that generated the observations. In this study, the outcome is a continuous count of high-effort selections, summarized in the registry as a mean with a standard error. The named contrast is placebo versus methylphenidate, while the study also distinguishes adults with ADHD from adults without ADHD. The record labels the design crossover and the allocation non-randomized. These features affect which comparisons are meaningful and what assumptions an analysis would need.

What does a mean describe?

A mean is a summary of the typical numerical level of an outcome across observations. Here, the outcome is the number of high-effort selections in the task. A mean can make groups or conditions easier to compare, but it does not show how individual responses are distributed. Participants can make different choices even when their group mean is similar, and a mean alone does not reveal whether results are concentrated or variable.

The standard error describes uncertainty in an estimated mean, rather than the spread of individual participant outcomes. It is useful for assessing how precisely a mean has been estimated under the analysis assumptions. The registry specifies standard error as the dispersion measure, but it does not report the numerical means or standard errors. Therefore, neither the outcome level nor its precision can be evaluated from the record.

Why does crossover structure matter?

In general, crossover studies compare conditions experienced in sequence, often allowing each participant to serve as their own reference. That structure can account for stable participant characteristics when the analysis uses paired observations appropriately. But measurements may also depend on when a condition was given, what condition came first, or whether an earlier condition influences a later one. These are commonly described as period, order, and carryover concerns. The registry reports counterbalanced order but does not state whether these effects were evaluated or how the analysis accounted for them.

Because allocation is listed as non-randomized, the treatment sequence should not be interpreted as a randomized allocation. Counterbalancing describes the distribution of treatment order; it is not a substitute for randomization. The registry’s own note says the arms are not a like-for-like control comparison. That warning is particularly relevant if sequence groups are compared as though they were randomized parallel groups.

What would an effect estimate and interval contribute?

In general, an effect estimate expresses the size and direction of a contrast on the outcome’s scale. A confidence interval adds information about statistical uncertainty and precision. A result with substantial uncertainty may be compatible with a range of effects, even if its point estimate appears notable. A p-value answers a different, narrower question about compatibility with a null hypothesis under specified assumptions; it does not quantify effect size or establish clinical importance.

The registry record does not report a primary endpoint estimate, confidence interval, p-value, or other inferential result. It lists zero analyses. Accordingly, there is no basis in the record for describing statistical significance, precision, or the direction of a treatment-condition result. The design and endpoint description cannot take the place of those results.

Why can over-dispersion matter for counts?

As a general statistical point, count outcomes can vary more than a simple model assumes. When observed variation exceeds the model’s expected variation, this is called over-dispersion. Ignoring it can make standard errors too small and intervals too narrow. The endpoint is a count of selections bounded by the task’s 50 trials, but the registry does not identify the model used, report a dispersion assessment, or provide an analysis. It is therefore not possible to say whether over-dispersion was present or how it was handled.

What can planning illustrations establish?

The registry describes sample-size assumptions for planning illustrations: a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and effects expressed as fractions of an observed effect. It states that non-time-to-event illustrations are expressed as participants per arm and that time-to-event illustrations use total events. These are planning assumptions, not evidence about the trial’s observed power. The observed effect and resulting numerical planning values are not reported in this record, and the registry does not report its own sample-size justification. Planning calculations cannot fill the gap left by missing endpoint results.

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("ADHD Subjects, Placebo Condition", "ADHD Subjects, Methylphenidate Condition", "Non-ADHD Subjects, Placebo Condition", "Non-ADHD Subjects, Methylphenidate Condition")
n   <- c(23, 23, 23, 23)
m   <- c(16.4, 21.35, 20.45, 19.8)
sp  <- c(2.2, 1.9, 2.2, 1.9)
sd  <- sp * sqrt(n)      # standard errors converted to SDs
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  ADHD Subjects, Placebo Condition  23  16.400  10.551  11.837  20.963
CARM  ADHD Subjects, Methylphenidate Condition  23  21.350  9.112  17.410  25.290
CARM  Non-ADHD Subjects, Placebo Condition  23  20.450  10.551  15.887  25.013
CARM  Non-ADHD Subjects, Methylphenidate Condition  23  19.800  9.112  15.860  23.740

11. Multiplicity, Missing Data and Analysis Populations

Multiplicity concerns arise when an analysis evaluates several outcomes, contrasts, subgroups, or time points. Repeated testing can increase the chance that at least one result appears noteworthy by chance. The registry lists one outcome measure, but it does not report a statistical analysis plan or explain whether additional comparisons were planned. It also does not report how multiplicity would be addressed. The primary endpoint’s numerical analysis is not reported, so the record does not allow readers to determine which comparisons were performed or how they were interpreted.

Missing-data handling is also not reported in the registry record. The endpoint description specifies measurement 1 hour post drug or placebo administration for each study session, but the record does not say whether any measurements were missing, how incomplete crossover observations were treated, or whether a particular analysis population was used. It does not describe an intention-to-treat, per-protocol, or other population for the primary analysis. These omissions matter because missing observations can affect both the estimated contrast and its uncertainty, especially when participants contribute observations under multiple conditions.

The registry reports enrollment of 51, but enrollment alone does not establish how many participants contributed usable endpoint data to each condition or analysis. No group-specific endpoint denominators or participant flow for the primary outcome are reported. Without those details, the completeness and representativeness of the analyzed observations cannot be assessed.

12. Safety Results

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

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 2.5% reporting threshold.

The registry lists four sequence groups: adults with ADHD receiving methylphenidate first and placebo second, adults with ADHD receiving placebo first and methylphenidate second, and the corresponding two sequences for adults without ADHD. For these groups, the record reports zero serious adverse events, zero other adverse events, and zero deaths. The serious-event and other-event risk counts listed for the groups are 12, 11, 11, and 12, respectively.

These entries describe what was reported to the registry for the listed groups. They do not establish that no symptoms or events occurred outside the categories or reporting procedures captured in the record. A zero count is not proof of zero underlying risk, and it should not be interpreted as evidence of safety in other populations or settings. The record does not provide event terms, severity details beyond the serious/other categories, exposure-adjusted summaries, or additional context about adverse-event collection. No serious adverse event terms are listed.

The groups represent treatment sequences in a non-randomized crossover study, not a randomized comparison of drug and placebo safety outcomes. The adverse-event counts therefore should not be read as a causal estimate of risk attributable to either condition. They are registry-reported counts, with the limitations of the available reporting detail.

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

The record establishes what the investigators set out to measure: high-effort choices during a structured effort-based decision task, under placebo and methylphenidate conditions, among adults with and without ADHD. It also describes the sequence structure, endpoint timing, and task demands. Those details make the research question understandable, but they do not answer it quantitatively.

The registry does not report numerical primary endpoint results or analyses. It is therefore not possible to state whether high-effort selections were higher or lower in one condition, how large any difference was, how precise an estimate might be, or whether a statistical test met a specified threshold. The record also does not provide a reported test of whether the treatment-condition pattern differed between the ADHD and non-ADHD groups. Statements about an effect or an absence of effect would go beyond the reported results.

Even if a task-level contrast were available, the outcome would represent behavior in the experimental task, not a direct measure of a participant’s everyday motivation or clinical status. The task involves button pressing, reward magnitude, reward probability, and a constrained response period. The registry explicitly notes that the clinical and/or physiological relevance of the results is not established. Any interpretation should remain at the level of the measured task behavior unless other evidence supports broader conclusions.

The design further limits causal interpretation. The registry labels allocation non-randomized and cautions that the arms are not a like-for-like control comparison. Treatment order was counterbalanced, but the record does not report details of the analysis of order, period, or carryover. These features do not invalidate the research question; they define what must be considered when interpreting any reported comparison. In this record, however, the central limitation is more basic: the numerical outcome and its analysis are not reported.

14. Why This Trial Matters Statistically

This study is statistically instructive because it combines a behavioral count outcome, a crossover structure, treatment-order sequences, and a comparison between adults with and without ADHD. Each feature calls for a different question of interpretation. The count measures task behavior; the crossover structure makes within-participant contrasts potentially relevant; the sequences make order important; and the participant groups define an additional comparison. A sound interpretation depends on keeping those contrasts distinct.

The record also illustrates why design labels should not be treated as interchangeable. Crossover describes the structure of conditions over time, whereas randomized allocation describes how assignments are made. This study is labeled crossover and non-randomized, and the registry warns that the arms are not a like-for-like control comparison. Counterbalanced order can be useful, but it does not remove the need to understand assignment and analysis procedures.

Another statistical lesson is that detailed endpoint definitions are not a substitute for results. The record explains the response task, the endpoint scale, and the measurement time, yet does not report means, standard errors, effect estimates, or inferential analyses. Without these, readers cannot evaluate magnitude or precision. Reporting the estimate alongside uncertainty and analysis details is essential for interpreting a continuous outcome.

Finally, the registry’s caution about clinical or physiological relevance distinguishes experimental behavior from clinical meaning. A task can be defined precisely and still have uncertain relevance beyond its setting. Keeping the measured construct, statistical contrast, and broader interpretation separate is especially important when numerical results and analysis details are unavailable.

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 registry record leaves several trial-specific uncertainties unresolved. Although it identifies the design as crossover and states that treatment order was counterbalanced, it does not report the interval between sessions, any washout procedure, or how period and carryover effects were assessed. These details can matter when a participant receives conditions in sequence. The masking label is double, but the record does not specify who was masked or how masking was maintained.

Allocation is explicitly non-randomized, and the registry cautions that the arms are not a like-for-like control comparison. The record does not explain the allocation process or provide an analysis plan that would clarify how group and sequence differences were handled. It also does not report participant flow, endpoint completeness, missing-data procedures, or analysis populations. Enrollment is reported as 51, but usable endpoint counts by condition are not reported in the registry record.

The registry describes a single primary outcome measure, yet lists zero analyses and does not report the endpoint’s numerical results. No effect estimate, uncertainty interval, or p-value is available in the record. It also does not provide a sample-size justification for the trial or explain whether interim analyses were planned. These items are not reported in the registry record.

Finally, the task is a basic science experiment involving effortful button pressing for a small financial reward. The registry states that clinical and/or physiological relevance is not established. This limits how far any task result could be generalized, even if its numerical estimate were available.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Motivated Behavior in Adults With and Without ADHD — NCT02630017.
• Registry record last updated 2021-08-27; status last verified 2021-08.
• Results first posted 2021-08-27.
• 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

The registry record describes a completed phase 2, non-randomized, double-masked crossover study sponsored by the University of Arkansas. Enrollment was 51. The study included adults with ADHD and adults without ADHD and used methylphenidate-first and placebo-first sequences, with order described as counterbalanced within each group.

The primary endpoint was the number of high-effort selections in an effort-based decision-making task, measured 1 hour post drug or placebo administration for each study session. The registry reports one outcome measure and zero analyses. Numerical primary endpoint results and inferential statistics are not reported in the registry record. The record lists zero serious adverse events, zero other adverse events, and zero deaths in the four sequence groups, and cautions that the clinical and/or physiological relevance of the task results is not established.