Impact of Helmet Use in Preschool Children: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Impact of Helmet Use in Preschool Children (NCT01054846), a randomized na study. The primary outcome is Percentage of Participants Wearing Helmet.

2. Clinical Question

3. Trial Design

This was a randomized, parallel-group trial with no masking listed in the registry. The two groups differed in whether children received a free bicycle helmet in addition to helmet education: the intervention group received both, while the comparison group received education alone. The registry lists enrollment as 609. It does not state how participants were randomized, whether allocation was concealed, or whether the two groups were intended to have equal numbers. Equal allocation is an assumption for the posted sample-size planning illustrations, not a reported feature of the trial design.

The listed study dates are 2008-05 for the start and 2008-11 for primary completion. The status is completed. The registry identifies head injuries and facial injuries as conditions and names Parkview Hospital, Indiana, as the sponsor. The listed phase is NA.

The primary outcome is percentage of participants wearing a helmet at baseline and 5 months. The description specifies that the analysis reflects participants who owned the helmet during each survey. That definition matters: the described outcome is not an injury rate, nor does it necessarily cover every enrolled participant. The registry does not report how ownership was established, whether the same children contributed at both surveys, or how changes in the population of helmet owners were handled.

The registry does not report the randomization procedure, allocation concealment, masking procedures beyond NONE, sample-size justification, or a detailed statistical analysis plan. It also does not report whether there were interim analyses. Those omissions limit what can be said about the trial’s operational and analytical safeguards.

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: Although 285 received Helmet Education only, 68 participants had prior helmet ownership and therefore were considered for further analysis.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Analysis reflect population that owned the helmet during each survey

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 Percentage of Participants Wearing Helmet, measured over Baseline (Survey 1) and 5 months (Survey 2).

The primary endpoint is the percentage of participants wearing a helmet, measured at baseline and 5 months. The registry defines the analysis population as participants who owned a helmet during each survey. This outcome directly addresses the stated question about whether free helmet distribution, added to education, changes helmet use relative to education alone. It is a behavioral measure, not a measure of injury prevention.

Percentages can make group-level helmet use easier to interpret than counts alone, particularly when the numbers of participants contributing to a survey differ. However, the meaning of a percentage depends on its denominator. Here, the registry’s ownership-based population definition means the percentage is about helmet wearing among helmet owners at each survey, rather than necessarily among all enrolled children. The record does not report the denominators, group-specific percentages, or a single comparison of change between groups.

The registry notes that the primary outcome has several categories or time points and was not reduced to one comparison. Consequently, the outcome title and timeframe identify what was measured, but do not establish the direction, magnitude, or precision of a treatment contrast. Those result details are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The record identifies a randomized, parallel-group design and a binary percentage outcome. It does not provide a detailed statistical analysis plan or the result of a single primary comparison. The following concepts explain how such outcomes are generally interpreted; they do not imply that any particular method was used in this trial.

What does a percentage measure?

General explanation: a percentage is a count meeting a stated condition divided by the count in the analysis population, expressed as a proportion. For helmet wearing, the condition is wearing a helmet, and the registry says the relevant population consists of participants who owned a helmet during each survey. The denominator is therefore central to interpretation. If the population included at baseline differs from the population at 5 months, a change in the percentages could reflect differences in who was assessed as well as changes in wearing behavior. The registry does not report the denominators or explain whether the same children were included in both survey populations.

How can groups be compared over time?

General explanation: repeated measurements can be described at each time point, or a prespecified analysis can compare changes between groups. These answer related but distinct questions. A comparison at 5 months asks how the groups differ at that assessment. A comparison of change asks whether their shifts from baseline differ. A model can also account for repeated measurements on the same participant, if that is appropriate to the design and data. The registry does not report which approach was used, and its note that the primary outcome has several categories or time points and was not reduced to one comparison means a single contrast cannot be recovered from the record description.

What does randomization contribute?

General explanation: random assignment is intended to make the groups comparable at the time of assignment with respect to both measured and unmeasured characteristics, on average. It does not guarantee identical groups in a particular trial, and it does not by itself resolve missing outcomes, non-adherence, or changes in the analysis population. The registry labels allocation RANDOMIZED, but does not report the sequence-generation method, concealment procedures, or the analysis population used for a group comparison. The primary endpoint’s ownership-based population definition deserves separate attention because it is narrower than simply referring to everyone enrolled.

Why do confidence intervals matter?

General explanation: a confidence interval presents a range of estimates compatible with the observed data under the model and its assumptions. A narrow interval indicates more precision than a wide interval, but precision does not establish that an estimate is important. A confidence interval for a difference in percentages would help readers assess both the estimated contrast and its uncertainty. No such estimate or interval is reported for the primary comparison in the registry record.

What is the role of a p-value?

General explanation: a p-value evaluates how unusual data at least as inconsistent with a null hypothesis would be if that hypothesis and the analysis assumptions were true. It is not the probability that the null hypothesis is true, and it does not describe the size of an effect. A p-value also cannot substitute for a clear effect estimate and its uncertainty. The registry record does not report a p-value for a single primary comparison, so statistical significance cannot be assessed from the posted primary-outcome description.

What do the planning assumptions mean?

The registry’s sample-size assumptions describe planning illustrations based on the observed effect, with a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation. They also state that the effect to detect is a stated fraction of the observed effect. These are assumptions for illustrations, not evidence of the trial’s original sample-size justification or a reported design feature. The record does not report the trial’s own sample-size justification. General explanation: such calculations estimate the sample size needed under specified assumptions; they do not show the probability that a completed trial detected an effect, and they are not observed power. A planning calculation based on an observed effect can be sensitive to uncertainty in that effect. The record’s instructions distinguish total event counts for time-to-event illustrations from participants per arm for other illustrations, but no planning output values are stated in the registry entries.

Why can over-dispersion matter?

General explanation: over-dispersion occurs when observed variability is greater than a statistical model assumes. If a model underestimates variability, standard errors may be too small and intervals or tests may appear more precise than warranted. This concept is relevant in some count-data analyses, but the primary outcome is a percentage, and the registry does not report a count model or an over-dispersion adjustment. It would therefore be inappropriate to imply that over-dispersion was present or that a particular correction was used.

Overall, the registry allows a description of the planned comparison and outcome definition, but not reconstruction of the primary statistical result. The analysis method, estimate, uncertainty, and handling of incomplete data are not reported in the registry record.

10. Multiplicity, Missing Data and Analysis Populations

The registry identifies a primary outcome with multiple categories or time points and states that it was not reduced to one comparison. It also lists a secondary outcome concerning the incidence of head and facial injuries by helmet-wearing status in helmet owners. The record lists two outcome measures and two analyses, but does not provide enough detail to determine how the comparisons were defined or whether any adjustment for multiple testing was planned or applied. A multiplicity strategy is not reported in the registry record.

General explanation: when several outcomes, time points, or group contrasts are examined, the chance of at least one apparently unusual result can increase if each is tested separately. Prespecifying a primary contrast and explaining any adjustment helps readers distinguish confirmatory questions from exploratory ones. The registry’s description does not identify a single reduced primary comparison, so the intended hierarchy among possible time-point comparisons is unclear.

Missing-data handling is not reported in the registry record. The outcome description refers to helmet owners at each survey, but does not state how many participants were assessed, how missing surveys were treated, or whether ownership status could be missing. The analysis population and missingness assumptions are therefore not clear. The registry also does not report whether the primary analysis followed assignment regardless of helmet receipt or use, or instead used another population definition. These details affect how a comparison should be interpreted and cannot be inferred from the randomized design label.

11. 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 0% reporting threshold.

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: falls from bicycle resulting in severe injury to seek emergency care (1.5%).

The registry lists 607 participants at risk for serious adverse events and 9 participants affected. It also lists the serious adverse event term Falls from bicycle resulting in severe injury to seek emergency care, with a reported value of 1.5%. These are the safety figures recorded in the registry; the record details do not give a group-specific breakdown or establish a comparison between the randomized groups.

The percentage should be read as the reported value attached to that event term, not as an estimate of the treatment effect. The registry does not report the event-term denominator, timing, or allocation by study group in the information available for this summary. It is therefore not possible to infer whether events differed between the helmet-and-education group and the education-only group, or to attribute the listed events to either intervention.

Deaths are not reported in the registry record. The serious-event figures alone do not describe all possible harms, and they do not establish a causal relationship between study participation and an event. They should be interpreted as the registry’s recorded safety information, with the missing detail about group assignment and event ascertainment kept in view.

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

The record establishes that a randomized, parallel-group trial compared a free bicycle helmet plus education with education alone among preschool children from low-income families in northeastern Indiana. It identifies helmet wearing at baseline and 5 months as the primary outcome and describes an additional question about head and facial injuries by helmet-wearing status. These details clarify what the trial set out to examine.

The primary outcome description is not itself a result. The registry notes multiple categories or time points and does not reduce them to one comparison. It does not report the group-specific helmet-use percentages, a contrast between groups, an estimate of change, or uncertainty around any estimate. The record therefore cannot establish whether helmet use differed, how large any difference was, or how precisely it was estimated. The injury outcome results are also not reported in the registry record.

General explanation: a trial’s design and outcome definition describe the question and the way it was measured; an estimate is needed to describe the observed answer. Uncertainty is needed to judge how precisely that answer is known. A statistically significant result, if one were reported, would still need to be considered alongside its size, uncertainty, and relevance to the stated question. None of these interpretive steps can be completed for an unreported comparison.

The enrollment figure of 609 should not be mistaken for the number contributing primary-outcome data at either survey. The registry defines the primary analysis around helmet owners at each assessment, but does not report the survey denominators. Nor does it explain missing-data handling or the exact analysis population for a randomized comparison.

Accordingly, the posted record supports a description of the trial question, design, and recorded safety counts. It does not support a conclusion about the effect of free helmet distribution on helmet use or injuries. Those questions require outcome estimates and analysis details that are not reported in the registry record.

13. Why This Trial Matters Statistically

This trial raises a useful statistical distinction between an intervention’s intended effect and the outcome actually measured. The intervention combined helmet distribution with education, while the comparison group received education alone. The primary outcome was helmet wearing, not head or facial injury. A change in wearing behavior and a change in injury incidence are different endpoints and require their own estimates and interpretations.

The population definition is also statistically important. Helmet use was assessed among participants who owned a helmet during each survey, rather than being described simply as a percentage of all enrolled children. Denominators and participant inclusion at each time point are needed to understand what each percentage represents and whether the groups remain comparable for the reported analysis. Those details are not reported in the registry record.

Another important issue is the choice of comparison. Baseline and 5-month measurements can be presented in several ways, including separate time-point summaries or a comparison of change. These approaches answer different questions. The registry’s note that the primary outcome has several categories or time points and was not reduced to one comparison makes the absence of a clearly reported contrast especially consequential for interpretation.

The registry also illustrates why a trial’s stated hypotheses should not be confused with its reported findings. It describes questions about both helmet use and injuries, but does not report the corresponding effect estimates. Clear reporting of the analysis population, contrast, uncertainty, and missing-data approach would allow readers to assess what the randomized comparison shows. Without those results, the design remains informative about the question asked, but not about its estimated answer.

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 main trial-specific limitation of the registry record is that it does not report a single primary comparison. It describes helmet use at baseline and 5 months, and explicitly notes that the primary outcome has multiple categories or time points that were not reduced to one comparison. Group-specific values, an effect estimate, and its uncertainty are not reported in the registry record.

The primary analysis population is described as participants who owned a helmet during each survey, but the record does not state how many children met that definition at each assessment or how the populations were identified. It does not explain whether the same participants contributed at both times. Missing-data procedures and the analysis population used for inference are not reported.

Although the trial is labeled randomized, the registry does not describe sequence generation, allocation concealment, adherence, or the statistical analysis plan. It does not report the sample-size justification or whether interim analyses were conducted. The planning assumptions listed for sample-size illustrations should not be treated as the trial’s original design justification.

The injury question is listed as a secondary outcome, but injury estimates and comparisons are not reported. Safety information includes a serious-event count and an event term, but the registry entries do not provide a group-specific breakdown. These omissions prevent assessment of the primary comparison, the injury question, and potential differences in recorded safety events.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Impact of Helmet Use in Preschool Children — NCT01054846.
• Registry record last updated 2017-02-09; status last verified 2017-02.
• Results first posted 2016-11-18.
• 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 registry record describes NCT01054846, Impact of Helmet Use in Preschool Children, a completed randomized, parallel-group trial with no masking listed. Enrollment was 609. The study began in 2008-05 and reached primary completion in 2008-11. Parkview Hospital, Indiana, is listed as sponsor.

The intervention group received a free Bell Sports Inc. bicycle helmet and helmet education; the comparison group received education without a helmet. The primary outcome was percentage of participants wearing a helmet at baseline and 5 months, among participants who owned a helmet during each survey. The registry does not reduce the outcome to one comparison or report its result. Head and facial injuries by helmet-wearing status are listed as a secondary outcome, without reported results in the registry record.

The safety record lists 607 participants at risk and 9 affected by serious adverse events, along with a reported 1.5% for the serious event term Falls from bicycle resulting in severe injury to seek emergency care. Group-specific safety results, deaths, detailed analysis methods, and missing-data procedures are not reported in the registry record.