DRIIVE (Data and Research on Interventions to Improve the Vehicular Environment): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for DRIIVE (Data and Research on Interventions to Improve the Vehicular Environment) (NCT02381626), a randomized na study. The primary outcome is Collect Preliminary Data on In-vehicle Excess Particulate Matter (PM) Exposure.

2. Clinical Question

The registry describes a study concerned with particulate matter in taxi cabs and possible links between in-cab air quality and lung or heart health risks. Its primary outcome, however, is an exposure-monitoring objective: monitoring and reporting particulate matter levels as time-averaged samples, using hourly averages, at work sites and homes across groups. That is distinct from measuring whether drivers developed lung or heart problems.

The intervention description indicates an initial period of measurement under usual conditions, followed by purifier placement for the intervention group. The wait-list group was not to receive a purifier at that time and was to undergo repeat monitoring and biological measurement. The record also lists questionnaires, a log-book, and urine samples among the interventions or study procedures. It does not report the results of those procedures.

The primary outcome population is explicitly described as having no data collected. Consequently, the registry record cannot answer whether purifier use changed particulate matter exposure, nor can it establish a connection between exposure and health outcomes. The question is relevant to exposure research, but the posted primary-outcome information is not an effect estimate.

3. Trial Design

DRIIVE is listed as a randomized, parallel-group study with no masking. The registry records enrollment of 39 and identifies the study status as completed. The listed start is 2014-12, and the primary completion date is 2020-10-18. The phase is recorded as NA. Memorial Sloan Kettering Cancer Center is listed as the sponsor.

The named groups are the Intervention Group and the Wait-list Control Group. The intervention description says that measurements, including biological markers and air monitoring, were taken under usual conditions during the initial 2 weeks. At the end of that period, portable HEPA air purifiers were to be placed in intervention-group drivers’ cars, with air monitoring and biological parameters repeated. The control description says that its drivers would not receive a purifier at that time and would also have air monitoring and biological parameters repeated for another 2 weeks. The registry wording for both arm descriptions is incomplete, so further procedural details are not reported in the registry record.

Questionnaires, a log-book, and a urine sample are also listed, alongside the HEPA purifier. The registry does not describe how randomization was generated or concealed, how participants were assigned, or whether the listed procedures were administered identically across groups. It also does not report adherence to purifier use or the monitoring schedule.

A peer non-driver group appears in the adverse-event record. The registry does not describe that group as an intervention arm in the available design information, so its role in the study’s primary exposure objective is not clear. The record’s completion status does not itself establish that the planned primary outcome was analyzed: the primary outcome population is marked as having no data collected.

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: Data were not collected

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 Collect Preliminary Data on In-vehicle Excess Particulate Matter (PM) Exposure, measured over 2 years.

The primary outcome is titled “Collect Preliminary Data on In-vehicle Excess Particulate Matter (PM) Exposure.” It is described as monitoring and reporting particulate matter levels using time-averaged samples, with hourly averages, at work sites and homes across all groups. Its stated timeframe is 2 years.

This outcome concerns exposure, not a clinical diagnosis or a measure of lung or heart disease. Particulate matter is described in the study summary as very small material in the air, including dust, smoke, dirt, and gas fumes. Measuring airborne particulate matter can characterize the environment participants encounter and can offer a basis for studying whether an intervention changes exposure. In general, a time average represents measurements over a period rather than a single moment; hourly averaging can describe variation at that time scale, while still smoothing shorter fluctuations.

The endpoint could therefore have addressed the study’s environmental question if measurements had been collected and reported. But the registry identifies the primary-outcome population as “Data were not collected.” It gives no particulate matter values, group summaries, variability estimates, or comparison results. The endpoint’s purpose and planned measurement approach can be described, but its observed level and any change associated with the purifier cannot be evaluated from the registry record.

The registry also mentions biological markers and biological parameters in the arm descriptions, but it does not identify them as the primary endpoint or report their results. They should not be treated as substitutes for the stated particulate matter outcome.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does randomization contribute?

In general, randomization assigns participants to study groups through a chance-based process. When carried out as intended, it can reduce systematic differences between groups at the time of assignment and support a fair comparison of outcomes. DRIIVE is described as randomized and parallel, but the registry does not report the random-sequence method, allocation concealment, or implementation details. Those omissions prevent a fuller assessment of how assignment was carried out. More fundamentally, the primary outcome data were not collected, so randomization cannot yield a treatment-effect estimate for that outcome in this record.

What is a parallel comparison?

In a parallel-group design, participants are assigned to a group and the groups are followed over the study period. The DRIIVE arm descriptions set out an intervention group and a wait-list control group, with an initial period under usual conditions and subsequent measurements. The record does not report whether the primary analysis was intended to compare post-intervention levels, changes from baseline, or another summary. It also does not report a statistical plan. Those choices matter because different comparisons answer different questions and may handle repeated measurements differently.

How should the repeated measurements be understood?

The arm descriptions refer to air monitoring and biological parameters measured under usual conditions and repeated after the initial 2 weeks. In general, repeated measurements can show how an outcome changes over time and may help distinguish a group difference at follow-up from a difference in change. Measurements from the same participant are usually related to one another, so an analysis should account for that within-participant relationship rather than treating every observation as independent. The registry does not report the number or timing of completed measurements, a method for handling within-person correlation, or any repeated-measures analysis. Since the primary data were not collected, these are design and analysis considerations, not methods confirmed to have been used.

Why does the hourly average matter?

The stated outcome uses time-averaged particulate matter samples described as hourly averages, monitored at work sites and homes across all groups. In general, averaging measurements over time reduces the influence of brief fluctuations and produces a summary for the averaging period. It can also conceal short-lived peaks. A useful interpretation depends on how instruments were operated, where samples were collected, how missing readings were handled, and whether measurements were comparable across locations and groups. These details are not reported in the registry record, and no measurements are posted.

What would an estimate and confidence interval tell a reader?

In general, an effect estimate describes the size and direction of a comparison, while a confidence interval describes the uncertainty associated with that estimate under the analysis assumptions. A narrow interval indicates greater precision than a broad interval, though precision alone does not establish practical importance or freedom from bias. For a particulate matter comparison, interpretation would require the estimate’s scale, the groups and time points being compared, and an uncertainty measure. None is reported for the primary outcome. There is therefore no basis to characterize either the size or precision of an intervention effect.

What does a significance threshold mean?

The registry’s planning assumptions mention a two-sided significance level of 0.05. In general, a significance level is a decision threshold used in a statistical testing procedure; it does not measure the probability that a hypothesis is true, and it does not describe the size or importance of an effect. The threshold alone is not a statistical analysis. Because no primary-outcome data or analyses are reported, there is no reported test statistic or p-value to interpret. The stated planning threshold should not be mistaken for evidence of an observed result.

How should planning calculations be read?

The record describes sample-size planning illustrations based on a stated fraction of an observed effect, with equal allocation between the two arms and a normal approximation. It specifies that the illustrations use a two-sided significance level of 0.05 and are planning calculations, not observed power. In general, such calculations can show what participant counts might be needed under chosen assumptions about an effect and variability. They are not a substitute for an observed treatment effect, and a planning illustration does not show that a study had a particular probability of finding a result. The registry does not report a primary-outcome estimate to interpret, so no effect-based planning illustration can establish what DRIIVE observed. The registry does not report a sample-size justification or further statistical plan.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome measure and no analyses. It does not report a statistical analysis plan, a hierarchy of outcomes, or a procedure for addressing multiplicity. In general, multiplicity arises when many outcomes, time points, groups, or analyses are tested; considering many tests can increase the chance of finding an apparently notable result by chance. The registry does not provide enough analysis information to determine whether this issue arose or how it would have been addressed. The primary outcome’s description refers to monitoring across groups and locations, but no outcome data or comparisons are reported.

Missing-data methods are not reported in the registry record. More importantly, the primary-outcome population is explicitly described as having no data collected. This is not a case in which the record reports partial outcome data and a method for imputing or otherwise handling missing observations; there is no posted primary outcome result to analyze. The registry does not explain why data were not collected or whether any related monitoring was completed outside the reported outcome.

The record does not define analysis populations, such as which participants would be included in a primary comparison or how departures from assigned intervention would be handled. The randomized design is reported, but an analysis population and analysis approach are not. The enrollment figure of 39 should not be treated as the number contributing to the primary outcome, because the record says primary data were not collected. The adverse-event counts are reported separately and do not establish an analysis population for efficacy or exposure outcomes.

11. 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 adverse-event record lists the Intervention Group, Wait-list Control Group, and Peer Non-driver group. For the Intervention Group, 17 were listed as at risk for serious adverse events and 17 for other adverse events; the record reports zero serious adverse events, zero other adverse events, and zero deaths. For the Wait-list Control Group, the corresponding at-risk counts are 16 and 16, with zero serious adverse events, zero other adverse events, and zero deaths. For the Peer Non-driver group, the corresponding at-risk counts are 6 and 6, again with zero serious adverse events, zero other adverse events, and zero deaths.

These figures describe what the registry reports; they are not a comparison of particulate matter exposure or a measure of the intervention’s effect. The record does not provide event definitions, collection procedures, monitoring duration, or details about completeness of safety reporting. A recorded zero should therefore be read as zero reported in this registry record, not as proof that no event of any kind occurred. The peer non-driver entry is a listed safety group, but its role in the primary outcome analysis is not reported.

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

The registry establishes that DRIIVE was designed as a randomized, unmasked, parallel study focused on air quality in taxi cabs and the possible role of portable HEPA air purifiers. Its primary outcome was intended to characterize particulate matter exposure through time-averaged monitoring, with hourly averages at work sites and homes across groups. The arm descriptions also refer to biological measurements, questionnaires, a log-book, and urine samples.

What the record does not establish is whether the intervention changed in-vehicle particulate matter exposure. The primary outcome population is marked as having no data collected, and the registry reports no analyses. There is no posted estimate, uncertainty interval, or statistical test for exposure. The record also does not report a result linking particulate matter exposure with lung or heart health, or a clinical health outcome comparing the groups.

This distinction matters: a research objective and a planned comparison are not findings. A completed status indicates the registry’s study status, but it does not replace outcome data. Likewise, the stated health rationale explains why the topic was studied; it is not evidence that a health risk changed during the study.

The listed adverse-event counts are a separate kind of information. The registry reports zero serious adverse events, zero other adverse events, and zero deaths in each listed group, but does not describe the detail needed to assess how those counts were collected. They cannot be used to infer an effect on particulate matter or health.

In general, an informative intervention comparison needs observed outcomes, a defined comparison, and a measure of uncertainty, together with enough methodological detail to understand how the analysis was conducted. Those elements are not reported for the primary outcome. The record therefore documents the study’s design and intended measurement question, but not an answer about purifier effectiveness or health consequences.

13. Why This Trial Matters Statistically

DRIIVE is statistically relevant because it brings together an environmental exposure question, a randomized intervention, and repeated monitoring. Such a design can, in general, support a comparison of exposure under intervention and control conditions, while measurements taken over time can help describe patterns that a single reading may miss. The registry’s focus on time-averaged particulate matter levels is suited to describing exposure at specified places and averaging periods, rather than directly measuring a clinical health outcome.

The record also illustrates why design descriptions and results must be read separately. Randomization is a feature of the planned comparison, but it does not ensure that a result is available or that the reported information answers every motivating question. Here, the primary outcome is explicitly marked as not collected, and no analyses are recorded. The absence of an estimate is not evidence of no difference; it leaves the intervention comparison unresolved in the registry record.

Another statistical lesson is the importance of specifying what an endpoint represents. In-vehicle particulate matter exposure is an environmental measure. It may be relevant to health research, but it is not itself a diagnosis or direct measure of health risk. The study summary discusses possible health relevance, while the primary outcome description concerns monitoring exposure. Keeping those concepts distinct prevents an exposure objective from being mistaken for a demonstrated clinical effect.

Finally, safety counts, intervention procedures, and outcome analyses answer different questions. The registry reports adverse-event counts, but those counts do not replace exposure measurements or a statistical comparison. The record’s limitations make transparent reporting of outcome collection, analysis populations, and uncertainty especially important for evaluating what the study can contribute.

14. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The most consequential limitation in the registry record is that the primary outcome population is described as having no data collected. There are consequently no reported particulate matter measurements or comparisons on which to base an estimate. The record does not explain why data were not collected, whether any monitoring was attempted, or whether the outcome was unavailable for another reason.

Although the study is listed as randomized and parallel, details of sequence generation, concealment, and assignment are not reported. Masking is listed as none. The registry does not describe whether monitoring personnel or analysts knew group assignments, or how that might have been handled. These details would matter when assessing how the intervention and measurements were implemented, but they cannot be resolved from the record.

The arm descriptions are incomplete. They mention the initial 2 weeks of usual-condition measurements and subsequent repeated monitoring, but do not give a full account of the procedures or timing beyond those statements. The record does not report purifier adherence, monitoring instrument details, measurement completeness, or participant-level exposure summaries. It also does not specify the relationship between the peer non-driver group and the primary outcome comparison.

No analysis plan, analysis population, missing-data method, or multiplicity approach is reported. The registry also gives no sample-size justification. The listed planning assumptions do not substitute for an observed outcome estimate or a documented design rationale. Finally, the safety record gives event counts but not definitions, ascertainment methods, or monitoring duration. These limitations restrict interpretation to the study’s stated design and the fact that its primary data were not collected.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: DRIIVE (Data and Research on Interventions to Improve the Vehicular Environment) — NCT02381626.
• Registry record last updated 2021-10-05; status last verified 2021-02.
• Results first posted 2021-10-05.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

18. Record Summary

The DRIIVE registry record describes a randomized, unmasked, parallel study sponsored by Memorial Sloan Kettering Cancer Center. It lists enrollment of 39, a start of 2014-12, primary completion on 2020-10-18, and status as completed. The study concerns particulate matter exposure in taxi cabs and the use of portable HEPA air purifiers.

The primary outcome is preliminary in-vehicle excess particulate matter exposure, measured as time-averaged samples using hourly averages at work sites and homes across groups, with a stated timeframe of 2 years. The primary-outcome population is marked as having no data collected, and no analyses are recorded. The registry reports zero serious adverse events, zero other adverse events, and zero deaths for each listed safety group. No primary exposure effect or health effect can be determined from the posted results.