Evidence-based Intervention for Improved Head Impact Safety in Youth Football - Aim 1 and Aim 3: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Evidence-based Intervention for Improved Head Impact Safety in Youth Football - Aim 1 and Aim 3 (NCT04908930), a non-randomized na study. The primary outcome is Number of Head Impacts.

2. Clinical Question

3. Trial Design

This was a completed, nonrandomized study registered as NCT04908930, with the title “Evidence-based Intervention for Improved Head Impact Safety in Youth Football - Aim 1 and Aim 3.” The official title is “Community-Engaged Sport Safety - Aim 1 and Aim 3.” Wake Forest University Health Sciences is listed as the sponsor. The recorded start date was 2021-07-08, and the primary completion date was 2023-10-22. The registry status is completed.

The study combines descriptive biomechanical data collection with a pilot intervention. In Aim 1, two middle school football teams were included. Interested athletes were invited to participate in biomechanical data collection, and a subset of enrolled athletes was to be randomly selected for head impact sensor instrumentation. In Aim 3, two new middle school teams were recruited to pilot the practice-structure intervention. Coaches were recruited and enrolled, and interested athletes were enrolled; a subset was selected for instrumentation. The record also describes baseline and post-season neurocognitive data collection.

The registry identifies the allocation as nonrandomized, the masking as none, and the model as sequential. It does not describe a randomized allocation between intervention and unexposed teams. Consequently, comparisons between the groups should be read as observational rather than as a randomized treatment contrast. Differences in team, participants, or context could be entangled with differences attributed to the practice structure.

The stated total enrollment was 106. The record does not specify the number included in the primary endpoint analysis, nor does it report how enrollment was distributed across all study activities. The study is listed as phase NA. A rationale for sample size, a detailed statistical analysis plan, and details of any interim analyses are not reported in the registry record.

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: Missing participants-- Unexposed practice group: 1 incompatible with mouthpiece, 1 quit team before contact, and 1 did not attend practice sessions. On-Field activity group: 1 incompatible with mouthpiece, 2 quit team before contact, 2 didn't like mouthpiece fit

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 Head Impacts, measured over Month 3.

The primary endpoint is the number of head impacts, expressed as the total number of practice impacts. It is described as a mean with standard deviation, with assessment at Month 3. The endpoint description says head impact data would be transformed to the head center of gravity using Matlab (Mathworks, Inc., Natick, MA) and quantified for practice sessions.

Counting impacts during practices gives the study a way to describe the biomechanical exposure measured by head impact sensors while athletes take part in football activities. The mean describes the central level of the measured counts in a group, while the standard deviation describes how spread out those measurements are around the mean. These are descriptive summaries; on their own, they do not establish that group differences are attributable to an intervention.

The registry record does not report the group means, standard deviations, or an estimated group contrast for this endpoint. It therefore does not show the observed level of practice impacts or the precision of any comparison. The record also does not give further details on the aggregation of sensor data into a participant-level endpoint or the handling of practice sessions with incomplete monitoring.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry characterizes the primary endpoint as continuous and summarizes it using a mean and standard deviation. For a continuous measure, the mean is the arithmetic center of the observed values, while the standard deviation describes their dispersion. In general, a larger standard deviation indicates more spread around the mean. These summaries can help describe head impact counts, but interpretation also depends on the unit of analysis, the amount of data collected per athlete, and how repeated practice sessions were handled. Those details are not reported in the registry record.

What does the endpoint measure?

The endpoint is the number of practice impacts, with head impact data transformed to the head center of gravity and quantified for practice sessions. Sensor-based measurements are the basis for this endpoint. In general, repeated measurements from the same athlete or team may be statistically related rather than independent. Analyses of such data often need to account for clustering or repeated observations; the registry does not report whether, or how, its analyses addressed these features. The record also does not describe how sensor readings were quality-checked or how periods without usable sensor data entered the endpoint calculation.

What can a mean and standard deviation tell the reader?

These summaries describe the observed data, not the cause of the observations. A mean can locate the group’s typical level in a concise way, while the standard deviation indicates variability among the values being summarized. Neither alone indicates uncertainty in the estimated mean or a between-group difference. A standard error or confidence interval would address estimation precision, but neither is reported for the primary endpoint. There is no basis in the registry record to reconstruct those quantities without inventing information.

How should the group comparison be understood?

The design is nonrandomized and sequential, with no masking. In general, random allocation can help balance measured and unmeasured participant characteristics across comparison groups. That protection does not arise from the design. The intervention group consists of new teams piloting the practice structure, while the Aim 1 group is described as unexposed players practicing as they otherwise would. A contrast between these groups would therefore be observational and could reflect group differences as well as the intervention. The registry does not report an adjustment strategy or a model for the primary endpoint.

Masking is listed as none. For a sensor-measured endpoint, the effect of that design feature depends on how participants, coaches, data collectors, and analysts interacted with the outcome process. The record does not explain who knew group assignment during data collection or analysis. No assumptions about the consequences of masking can therefore be made for this specific study.

What do the planning assumptions mean?

The record describes planning illustrations based on the observed effect, using a two-sided significance level 0.05, equal allocation between two arms, and a normal approximation. In general, such calculations describe the number of participants that a hypothetical design might require to detect a specified effect under its assumptions. Rows framed around fractions of an observed effect represent planning for a smaller target effect than the full observed estimate. These are planning illustrations, not observed power and not evidence about the study’s endpoint results. The record does not report its sample-size justification or the numeric outputs of the planning illustrations.

In general, a significance level sets a threshold for a particular statistical testing procedure; it does not state the probability that a result is true. Equal allocation is an assumption about the balance of participants between groups in a hypothetical planning calculation, not a claim about the actual group sizes. A normal approximation is a mathematical simplification whose suitability depends on the data and design. The registry does not report enough information to assess whether those assumptions match the collected head impact data.

What is not available for evaluation?

The record does not report an analysis model, a primary endpoint contrast, a confidence interval, a p-value, or an analysis population for the primary endpoint. It does not state how missing sensor observations were treated, whether the analysis adjusted for team or repeated practice observations, or whether any sensitivity analyses were conducted. Interim analyses are not reported in the registry record. These omissions limit assessment of the statistical methods and the precision of any conclusion.

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("Unexposed Practice Group- Aim 1", "On-field Activity Group - Aim 3")
n   <- c(33, 29)
m   <- c(100.24, 50.27)
sp  <- c(81.06, 39.57)
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  Unexposed Practice Group- Aim 1  33  100.240  81.060  71.497  128.983
CARM  On-field Activity Group - Aim 3  29  50.270  39.570  35.218  65.322

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 61 outcome measures, including the primary number-of-head-impacts measure and secondary measures of feasibility, acceptability, intervention implementation, changes to the intervention, and neurocognitive performance. Many outcomes can create a multiplicity issue: when several outcomes are tested, the chance of at least one apparently notable result can increase. In general, a prespecified outcome hierarchy or an adjustment strategy can help readers understand how multiple comparisons were handled. Such a strategy is not reported in the registry record, and no analysis results are listed.

The study description identifies some missing sensor data and gives reasons for nonparticipation in the unexposed and on-field activity groups. Reasons include mouthpiece incompatibility, leaving the team before contact, and not attending practice sessions. These details indicate that not every enrolled athlete necessarily contributed sensor data. The record does not report the complete primary endpoint analysis population, the amount of missing endpoint data, or whether missingness was handled through exclusion, imputation, or another method. The number enrolled should therefore not be assumed to equal the number contributing to the endpoint analysis.

The record describes baseline and post-season neurocognitive data collection, but does not report how missing observations for these secondary outcomes were handled. It also does not report whether an intention-to-treat, per-protocol, or other analysis population was defined. Those analysis-population definitions and the handling of incomplete observations are not reported in the registry record.

Because no analyses are listed, readers cannot determine whether multiplicity adjustments or missing-data methods were used outside the registry record. Their absence from the record should not be treated as evidence that no such work occurred; it means the methods are not documented there.

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 0% reporting threshold.

The registry lists five groups for adverse event reporting: the unexposed practice group, the on-field activity group, and three stakeholder groups. It reports zero serious adverse events and zero other adverse events in each listed group, as well as zero deaths in each group. The numbers at risk are 36 in the unexposed practice group, 34 in the on-field activity group, 6 in the unexposed practice group stakeholders, 12 in the on-field activity group stakeholders, and 18 in the other unexposed stakeholder group.

These figures describe the events recorded in the registry for the listed groups. They are not a measure of the primary endpoint, which concerns practice head impacts, and they do not establish that no event could have occurred outside the registry’s reporting process. The record does not provide further detail on adverse event definitions, surveillance procedures, or the period during which each group was monitored. No serious adverse event terms are listed.

Zero recorded events should be read as a count, not as proof of zero risk. In general, when no events are observed, the data still do not rule out events in a broader population. The registry’s adverse event summary does not report an inferential comparison between groups.

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

The registry record documents a completed, community-engaged study that collected or planned to collect practice head impact data and piloted a practice-structure intervention with youth football teams. It identifies a primary endpoint, its unit, summary measure, and assessment timeframe. It also describes stakeholder engagement and a set of feasibility, implementation, and neurocognitive outcomes. These details clarify the study’s focus and the kinds of information it was designed to gather.

The record does not, however, report the primary endpoint values or a statistical comparison between the intervention and unexposed groups. It therefore cannot establish the direction or size of any difference in head impact counts, nor how precise such a difference might be. No treatment-effect claim can be drawn from an endpoint definition alone. The lack of a reported analysis is not evidence of no effect or of equal results.

The nonrandomized design further limits causal interpretation. In general, group differences in a nonrandomized study may reflect differences in the teams or their circumstances in addition to any intervention. The registry does not report adjustment methods that would help address these concerns, and it does not identify an analysis population for the primary outcome.

The posted adverse event counts are zero for serious events, other events, and deaths in each listed group, but those counts are not a substitute for a complete account of endpoint results or a quantified assessment of risk. The record also does not provide detailed outcome estimates for feasibility, acceptability, implementation, intervention changes, or neurocognitive measures.

Overall, the record supports a description of study design and measurement aims, not a conclusion about the intervention’s effect on practice impacts or on neurocognitive outcomes. The results and statistical details needed to answer those questions are not reported in the registry record.

14. Why This Trial Matters Statistically

This study is statistically notable because its design joins biomechanical monitoring with a community-engaged pilot. Head impact sensors were used to quantify practice impacts, while stakeholders—including parents, coaches, and league officials—were involved in discussions, focus groups, interviews, or intervention pilot activities. This combination brings measurement and implementation questions into the same study context.

The primary endpoint is a count-like measure summarized as a mean and standard deviation. In general, the distribution of counts may be uneven or have more variability than a simple normal model assumes; over-dispersion means that variability exceeds what a chosen model expects. If that occurs, standard errors and confidence intervals from an unsuitable model can be misleading. This is a general statistical consideration, not a finding about these data. The registry does not report the distribution of the recorded impacts or the model used to analyze them.

The sequential, nonrandomized design also illustrates why a clear distinction between descriptive and causal inference matters. Comparing groups can be informative about what was observed, but teams that differ in other ways can also differ in their measurements. The design information alone cannot separate those explanations. Without a reported endpoint analysis and its uncertainty, readers cannot judge the magnitude or precision of a comparison.

Finally, the study description highlights the practical importance of missing sensor data: some participants were not included because of mouthpiece fit, leaving before contact, or not attending practices. Such issues can affect both the number of usable measurements and the population represented by them. Reporting how those observations were handled would help readers assess the endpoint analysis. The registry record documents the data-collection context, but not those analytic details.

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 most direct limitation for statistical interpretation is that the registry record does not report results for the primary endpoint. The group means, standard deviations, contrast, confidence interval, and p-value are not reported in the registry record. With no listed analyses, the reader cannot assess the size, direction, or precision of the primary comparison.

The allocation was nonrandomized, with no masking, and the study model was sequential. The groups therefore cannot be treated as randomized, interchangeable arms. The intervention was piloted by new teams, while the unexposed practice group was described separately. General differences between teams, participants, or practice settings may complicate any direct comparison; the record does not report how these factors were addressed.

The registry describes head impact sensor data collection but does not report the endpoint analysis population, a complete account of missing endpoint data, or methods for handling missingness. It gives several reasons for athletes not contributing sensor data, including incompatible mouthpiece fit, leaving the team before contact, and missing practice sessions. It does not report whether missingness was associated with participants’ impact measurements or how this possibility was assessed.

Additional limitations of the available record include no reported statistical analysis plan, sample-size justification, interim-analysis details, model specification, or multiplicity strategy. These items are not reported in the registry record. The record lists many secondary outcomes but does not include their results in the information summarized for this study. Together, these limitations restrict evaluation of both the primary endpoint and the broader set of study aims.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Evidence-based Intervention for Improved Head Impact Safety in Youth Football - Aim 1 and Aim 3 — NCT04908930.
• Registry record last updated 2025-02-27; status last verified 2023-03.
• Results first posted 2025-02-27.
• 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

NCT04908930 is a completed, nonrandomized study sponsored by Wake Forest University Health Sciences. It examined community-engaged sport safety in youth football through biomechanical data collection and a pilot practice-structure intervention. The registry records total enrollment of 106, no masking, and a sequential model. The primary endpoint was the mean number of practice head impacts at Month 3, with standard deviation as the dispersion measure.

The record describes two middle school teams in Aim 1 and two new teams in Aim 3, as well as stakeholder activities and secondary feasibility, implementation, and neurocognitive outcomes. It lists zero serious adverse events, zero other adverse events, and zero deaths in each adverse-event group. Primary endpoint results, inferential analyses, and detailed statistical methods are not reported in the registry record.