Reactions of Older Adults Driving After Cannabis Exposure: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Reactions of Older Adults Driving After Cannabis Exposure (NCT04629716), a registered phase not stated study. The primary outcome is Simulated Driving Performance Task Measuring Divided Attention.

2. Clinical Question

The study focused on adults aged 50 and older and recruited participants in the context of severe or chronic pain. Its central outcome was performance on a simulated driving task, rather than observed driving on public roads. The protocol summary also describes response time, attention, and executive functions as areas of interest, and identifies unwanted effects as a secondary outcome.

The registry record describes a prospective repeated-measures experimental study with assessments before medical marijuana initiation and after initiation. The comparison is not randomized in the record: allocation is not stated, and the registry explicitly warns that the arms are not a like-for-like control comparison. Consequently, the clinical question is best read as an investigation of associations and measured change, not as a definitive causal comparison of cannabis use with nonuse.

Although the registry record gives the primary endpoint definition, it does not report the group means, standard deviations, or an estimated contrast for the endpoint. The magnitude and precision of any difference in divided-attention performance therefore cannot be assessed from the reported outcome information.

3. Trial Design

The registry record describes a prospective repeated-measures experimental study of medical marijuana use and driving performance in adults aged 50 and older. Participants were assessed at baseline before medical marijuana initiation, at 1 month after initiation, and at 3 months after initiation. Electronic medical review was also planned at baseline and at the follow-up assessments.

The intervention group was described as adults with severe or chronic pain who were newly registered for the Medical Marijuana Registry in Florida and had no prior history of medical marijuana use. The control group was described as adults with severe or chronic pain and no prior history of medical marijuana use; it was intended to be matched on age, sex, and race. The record does not state how allocation to the groups occurred. It specifically cautions that this was not a randomized comparison and that the arms are not a like-for-like control comparison.

The protocol summary says investigators proposed enrolling 60 adults, with n=30 medical marijuana users and n=30 matched controls. The registry record lists enrollment as 44. These figures describe the proposed and recorded enrollment, respectively; they do not establish how many participants contributed to each primary-outcome analysis. The primary outcome population description says each group lost a few participants to follow-up at T2.

The primary outcome was analyzed at T2, corresponding to 1 month. Assessments were also planned at T3, corresponding to 3 months. The listed primary measure was a mean score from a simulated divided-attention driving task. The protocol summary names finite mixture modeling and generalized linear modeling accounting for individual and group-level outcomes as planned methods. The specific model used for the reported endpoint, if any, is not reported in the registry record.

The study status is COMPLETED. The registry record lists the study start as 2021-04-23 and primary completion as 2023-08-17. Completion status does not by itself indicate that numerical outcome findings or a complete statistical analysis are reported.

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:

Analysis population for the primary outcome, as defined in the registry: Primary outcome was analyzed at T2 and each group lost a few participants to follow-up.

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 Simulated Driving Performance Task Measuring Divided Attention, measured over 1 month.

The primary endpoint is the mean score on a simulated driving performance task measuring divided attention at 1 month. During the simulated drive, participants encountered 4 divided-attention task events. The score ranged from 0-4: 0 indicated that all tasks were missed, while 4 indicated that all tasks were completed. Higher scores represented better divided attention, meaning that the participant attended to more events while driving in the simulator.

The registry description gives a reason for using a simulator: it permits systematic presentation of events and manipulation of conditions, with stimulus presentation that allows analysis under similar conditions. The description also states that studies of driving simulators have shown them to be a valid predictor of on-road driving performance. The endpoint is therefore a controlled measure of task performance intended to inform understanding of driving-related functioning, not a direct record of actual on-road driving.

The measure is continuous in the registry’s statistical classification, and the specified summary is a mean with standard deviation. A mean describes the group’s average score; a standard deviation describes the spread of individual scores around that average. Neither statistic is reported for the primary outcome in the registry record. The endpoint definition explains how to interpret the scale, but it does not show the observed scores or the size and precision of a comparison between groups.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does the outcome measure?

The primary measure is a mean score on a continuous scale for simulated divided attention. Its values range from 0-4, with higher scores representing better task performance. The registry specifies a standard deviation as the dispersion measure. General: a mean provides a concise description of the center of a group’s scores, while a standard deviation describes how much those scores vary around the mean. Neither alone estimates the uncertainty in a difference between groups.

The registry record does not include the primary outcome means or standard deviations. It also does not report a confidence interval or p-value for the endpoint. General: an estimated difference describes the contrast between groups, while a confidence interval describes the uncertainty around that estimate under the analysis assumptions. A p-value addresses compatibility of the data with a specified null hypothesis under a statistical model; it does not measure the size or practical importance of an effect.

What does the record say about modeling?

The protocol summary names finite mixture modeling and generalized linear modeling accounting for individual and group-level outcomes as planned approaches. This indicates the kinds of methods investigators proposed, not necessarily the methods used for the posted primary endpoint. The record does not report the model specification, the outcome distribution or link function, the covariates included, or fitted estimates.

General: a generalized linear model can relate an outcome to explanatory variables while allowing a chosen outcome distribution and link between the model’s linear predictor and its expected value. The suitability of a particular specification depends on the outcome and analysis question. A finite mixture model can represent data as arising from more than one latent subgroup or component. Such models require decisions about model form and interpretation; those details are not reported in the registry record. The method names alone do not reveal how the analysis was implemented or whether it produced a reliable estimate.

The protocol summary also says modeling would account for individual and group-level outcomes. General: repeated measurements from the same person are often statistically related, so an analysis may need to account for that dependence rather than treat every observation as independent. The registry record does not state the correlation structure or the exact approach used to handle repeated measurements.

How should the nonrandomized comparison be read?

The record states that allocation is not stated and warns that the arms are not a like-for-like control comparison. General: random allocation, when used and implemented appropriately, is intended to balance measured and unmeasured characteristics across groups on average. In a nonrandomized comparison, group differences can reflect the exposure of interest, other differences between participants, or a combination. Matching on age, sex, and race is described as intended for the control group, but matching does not establish balance on every potential confounder.

The protocol summary says potentially confounding disease, treatment, and sociodemographic characteristics would be examined. The registry record does not report the results of those examinations or identify which variables were included in any adjusted analysis. It is therefore not possible to determine from the record whether or how confounding was addressed in an outcome estimate.

What can be concluded from the reported statistical information?

The record gives a continuous outcome classification, a mean as the summary measure, and standard deviation as the dispersion measure. It does not provide the numerical primary outcome results. The record also lists 0 statistical analyses. This means the available record does not give a reported analysis from which an effect estimate or uncertainty measure can be interpreted; it does not establish what analyses may have occurred outside the registry entry.

General: statistical significance and effect size answer different questions. A small p-value, if reported, would not by itself show that an effect is large, while a non-significant p-value would not establish that groups are equivalent. Interpretation usually depends on the estimated magnitude, its precision, the design, and the quality of outcome and missing-data reporting. None of the primary outcome estimate or precision information needed for that assessment is reported in the registry record.

The study’s listed assessment schedule creates a repeated-measures setting, but the primary endpoint population description says the outcome was analyzed at T2. The record does not state whether the primary analysis used only T2 data, incorporated earlier measurements, or used a model that jointly represented assessments. That analytic detail is not reported in the registry record, so the planned repeated-measures design should not be confused with a fully described repeated-measures analysis.

What do planning illustrations mean?

The record describes sample-size assumptions for planning illustrations based on an observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation. General: a planning illustration estimates the sample size that would be needed under stated assumptions and a target effect. It is not an observed outcome and is not evidence that the study had a particular probability of detecting an effect. The illustrations are not the trial’s own design justification, according to the record.

The numeric planning-illustration results and an observed effect used in those calculations are not reported in the registry record. Therefore, no particular required sample size or detectable effect can be interpreted from the available record. Such calculations depend on assumptions about the target effect, variability, statistical test, allocation, and analysis. A change in an assumption can change the planning result. General: over-dispersion, when present, means the data vary more than a chosen model allows; ignoring it can make uncertainty estimates too small. The record does not state whether over-dispersion was assessed or how it would be handled.

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("Intervention", "Control")
n   <- c(19, 19)
m   <- c(3.42, 2.57)
sp  <- c(0.67, 0.98)
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  Intervention  19  3.420  0.670  3.097  3.743
CARM  Control  19  2.570  0.980  2.098  3.042

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists 2 outcome measures and identifies unwanted effects of marijuana use as a secondary outcome. The primary outcome is the simulated divided-attention score at 1 month. The record does not report a prespecified multiplicity procedure, such as an adjustment for testing more than one outcome or comparison. Whether any adjustment was planned or applied is not reported in the registry record.

The protocol summary describes several areas of interest, including driving errors involving response time, attention, and executive functions, and unwanted effects. It also mentions examining whether type, frequency, dosage, or route of administration is associated with unwanted effects. The registry record does not give a complete statistical analysis plan for these questions, including the number of tests, their hierarchy, or how results would be interpreted together. No analyses are listed in the analysis count.

Missing-data information is limited. The primary outcome population description states that each group lost a few participants to follow-up at T2. Exact numbers missing, reasons for loss, and participant characteristics related to missingness are not reported in the registry record. The record does not describe whether missing outcomes were excluded, imputed, or handled through a model, and it does not report a sensitivity analysis.

The registry record does not define analysis populations, such as an intention-to-treat population or a population restricted to participants with observed outcomes. The enrollment figure of 44 is not a substitute for the number included in the primary analysis, particularly because the record notes loss to follow-up at T2. Accordingly, the analysis denominator and the consequences of missing outcome data cannot be determined from the reported information.

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 5% reporting threshold.

The registry record lists 0 serious adverse events among 23 participants at risk in the intervention group and 0 among 21 participants at risk in the control group. Other adverse events are also listed as 0 among 23 participants at risk in the intervention group and 0 among 21 participants at risk in the control group. Deaths are listed as 0 in each group. These figures describe the safety counts entered in the registry.

A zero count means that the registry lists no events of that category for the stated at-risk group. It does not establish that an event is impossible, or that a treatment is free of risk. Rare events may not appear in a study of this size, and the record does not provide detailed information about how adverse events were collected, monitored, or attributed. The serious adverse event terms list is empty, so no serious-event terms are reported.

The groups were not described as a randomized, like-for-like comparison. The counts should therefore not be interpreted as a causal estimate of comparative safety. The record also identifies unwanted effects as a secondary outcome but does not provide a detailed results analysis for that outcome. The adverse-event entries are a limited account of recorded events, not a comprehensive basis for evaluating safety.

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

This registry record is informative about the study’s question and measurement approach. It describes adults aged 50 and older with severe or chronic pain, a medical marijuana intervention group, a control group, and a primary measure of divided attention during a simulated drive. It also gives the score range and explains that higher scores indicate better performance on the simulator task.

The record does not report the primary outcome values or a statistical comparison. It therefore does not establish whether the groups differed in simulated divided-attention performance, how large any difference was, or how precisely it was estimated. The score description cannot substitute for observed outcome data. Nor can the completed status alone establish that numerical results were reported.

The design information also limits causal interpretation. The registry record says allocation is not stated and warns that the arms are not a like-for-like control comparison. Even a reported difference could reflect characteristics of the groups beyond medical marijuana use. The summary says potentially confounding disease, treatment, and sociodemographic characteristics would be examined, but adjusted estimates and the details of those analyses are not reported in the registry record.

The endpoint is simulator performance, not actual driving behavior on public roads. The registry description says simulators have been shown to be a valid predictor of on-road performance, but a simulator score remains a measure from a controlled task. It should not be treated as a direct account of real-world driving outcomes.

The record lists 0 serious adverse events, 0 other adverse events, and 0 deaths in the stated groups. These counts do not prove the absence of potential harms. In combination, the available information supports understanding the planned question and recorded event counts, but not a conclusion that medical marijuana improves or worsens driving performance or that it is safe or unsafe.

14. Why This Trial Matters Statistically

The study raises a statistical question that is relevant to interpreting performance measures: how to compare groups when participants are assessed over time and the exposure is not randomly allocated. The protocol describes baseline, 1-month, and 3-month assessments. Repeated measurements can provide information about change within participants as well as differences between groups, but their interpretation depends on the analysis and on how dependence among observations is handled. The registry record names planned modeling approaches without reporting the fitted primary-outcome analysis.

The comparison also illustrates why design details matter as much as model names. The registry says the control group was intended to be matched on age, sex, and race, while also warning that the arms are not a like-for-like comparison. Statistical adjustment can address measured differences only to the extent that they are measured and modeled appropriately; it does not ensure that all sources of group difference have been removed. The registry record does not report the covariates or adjusted estimates.

The primary endpoint uses a bounded score from 0-4, with higher values indicating better divided attention in the simulator. Its direction is clear, but the registry record does not report the mean scores, variability, or contrast. This is a useful reminder that a clearly defined scale does not, by itself, provide evidence about the observed outcome or its precision.

Enrollment is listed as 44, while the protocol summary proposed 60 adults. The primary outcome description also notes loss to follow-up at T2. Because exact analysis counts and missing-data methods are not reported, the recorded enrollment cannot resolve how much information contributed to the primary endpoint.

Statistically, the study is important to read as a question about measurement, group comparability, repeated observations, and incomplete follow-up—not as a numerical finding about driving performance. The registry record offers relevant design context, while leaving the primary outcome result and its uncertainty unreported.

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 the primary outcome is that the registry record does not report numerical results. It gives the endpoint definition and statistical summary type, but not the means, standard deviations, effect estimate, confidence interval, or p-value. The direction, magnitude, and precision of a primary-outcome comparison therefore cannot be evaluated.

The registry record warns that this is not a randomized comparison, states that allocation is not stated, and says the arms are not a like-for-like control comparison. Although the control group was intended to be age, sex, and race matched, matching on those characteristics does not establish equivalence in other respects. The summary says potential disease, treatment, and sociodemographic confounders would be examined, but the results and any adjustment details are not reported.

Follow-up information is incomplete for assessing the primary analysis. The record says each group lost a few participants at T2, but exact counts, reasons for loss, missing-data handling, and analysis populations are not reported. The listed enrollment of 44 cannot establish the outcome-analysis denominator.

The primary endpoint is performance on a simulator task. Although the registry description gives a rationale for using simulation, the outcome is not a direct measurement of on-road driving. The record also does not provide detailed results for the secondary unwanted-effects outcome or a complete statistical analysis plan, including multiplicity and model specifications.

Finally, the protocol summary proposed enrollment of 60 adults, while the record lists enrollment as 44. The record does not explain this difference, so no reason for it should be inferred. Taken together, the design cautions, missing analysis details, follow-up losses, and absence of numerical endpoint results limit the conclusions that can be drawn from the registry entry.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Reactions of Older Adults Driving After Cannabis Exposure — NCT04629716.
• Registry record last updated 2025-03-24; status last verified 2025-03.
• Results first posted 2025-03-24.
• 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

NCT04629716, titled Reactions of Older Adults Driving After Cannabis Exposure, is sponsored by Florida State University. The official title is Medical Marijuana Use and Driving Performance: A Test of Psychomotor Function in Adults 50 and Older. The registry lists chronic pain as the condition and the study status as COMPLETED.

The record describes a prospective repeated-measures study of adults aged 50 and older, with baseline assessment before medical marijuana initiation and follow-up at 1 month and 3 months. The primary outcome is the mean score on a simulated divided-attention driving task at 1 month. Scores ranged from 0-4, with higher scores indicating better task performance.

Enrollment is listed as 44; the protocol summary proposed 60 adults. The record states that each group lost a few participants to follow-up at T2. Allocation is not stated, and the registry cautions that the arms are not a like-for-like control comparison. Numerical primary-outcome results, analysis details, and missing-data methods are not reported in the registry record. The safety entries list 0 serious adverse events, 0 other adverse events, and 0 deaths in each group.