Longitudinal Follow-up of High School Athletes: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Longitudinal Follow-up of High School Athletes (NCT02432183), a registered phase not stated study. The primary outcome is Maximal Fall in Forced Expiratory Volume in One-second (FEV1) After Eucapnic Voluntary Hyperventilation (EVH) Test.

2. Clinical Question

3. Trial Design

The record describes a longitudinal follow-up study of high-school athletes and age-matched controls. It lists football players and basketball players recruited from the topsportschool in Leuven, swimmers recruited from the future team of the Flemish Swimming Federation, and a control group. The stated enrollment is 134. The record gives a study start of 2012-09, primary completion of 2015-06, and a status of completed.

The study summary describes assessment of lung function and airway inflammation at the start of elite sport school and changes after 1 and 2 years. The primary endpoint, however, is specified as the percentage change in FEV1 after EVH compared with baseline, with measurements through 15 minutes after the test. These are related descriptions of the study, but the record does not provide enough detail to establish how the longitudinal visits and the primary endpoint analyses were linked.

Allocation is not stated, and the record does not describe randomized assignment. The listed groups therefore should not be read as randomly assigned treatment arms. In particular, the control group is not necessarily a like-for-like comparison: its activity threshold is described as <4 hours/week in the brief summary and >4 hours in the group description. That inconsistency is not resolved in the registry record.

The record classifies the study as “other.” It does not report a statistical analysis plan, a sample-size justification, or details about how participants were selected beyond the group descriptions. The sample-size assumptions described for planning illustrations are not evidence of the original design or of an observed trial effect.

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: As we did not anticipate a gender imbalance in the study groups, control subjects were recruited based on age-match not on sex-match. To correct for the gender imbalance, we added nine control subjects to the control group.

Overall Study

Analysis population for the primary outcome, as defined in the registry: EVH test not correctly performed (according to measure description) in 11 subjects (5 football players, 4 basket ball players and 2 swimmers) and hence 11 subjects here excluded from analysis

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 Maximal Fall in Forced Expiratory Volume in One-second (FEV1) After Eucapnic Voluntary Hyperventilation (EVH) Test, measured over change from baseline compared to 15 minutes after EVH test.

The primary endpoint is the maximal fall in forced expiratory volume in one second (FEV1) after an eucapnic voluntary hyperventilation (EVH) test, expressed as a percentage change from baseline. FEV1 is a measure of how much air a person can forcefully exhale in one second. The record describes EVH as a six-minute challenge at a target ventilation of 85% of maximal voluntary ventilation. FEV1 is measured immediately after the challenge and at 5, 10 and 15 minutes.

The endpoint is intended to capture a change in lung function after a standardized respiratory challenge, rather than a measurement of lung function at rest alone. The registry description says a reduction in FEV1 of at least 10% at one of the post-test time points, compared with before the test, is considered positive. Salbutamol is given after the final post-EVH spirometry to assess bronchodilator reversibility.

The endpoint is specified as a median with an inter-quartile range, so its planned descriptive summary is based on the distribution of individual percentage changes. The record says the primary analysis excluded 11 subjects whose EVH test was not correctly performed: 5 football players, 4 basketball players and 2 swimmers. It does not report the resulting medians, inter-quartile ranges, or group comparisons. The endpoint definition alone therefore does not establish what changes were observed.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does the endpoint summary describe?

The primary measure is the maximal percentage change in FEV1 after EVH, summarized as a median and inter-quartile range. A median describes the middle of an ordered set of observations; the inter-quartile range describes the spread of the central portion of that set. These summaries can be useful when values are skewed or when extreme observations make a mean less representative. They do not, by themselves, show whether groups differ. A comparison requires an estimate of the difference or another appropriate contrast, together with information about its uncertainty.

The registry record does not report the endpoint’s median or inter-quartile range for any group. It also does not report a contrast, confidence interval, or p-value. Thus, the specified summary statistic describes how the outcome was intended to be presented, not what the study found.

Why does the EVH measurement schedule matter?

The description calls for FEV1 measurement immediately after EVH and at 5, 10 and 15 minutes, and defines the endpoint as the maximal fall. A maximum taken across repeated measurements is different from selecting one fixed time point: it uses the most pronounced value in the described set of post-challenge measurements. This makes the procedure and the availability of measurements at each time point important to the endpoint. The record does not explain how the maximum was handled when one or more post-test measurements were unavailable, or whether all scheduled measurements were obtained for each analyzed participant.

The description also states that an EVH test not correctly performed according to the measure description led to exclusion from the primary analysis. Excluding an invalid test can protect the intended measurement from procedural problems. At the same time, exclusions change which participants contribute to the analysis. The record does not report an analysis that includes those participants, or otherwise assess whether their exclusion influenced the results.

What can a confidence interval tell readers?

In general, a confidence interval gives a range of values compatible with an estimate under the assumptions of the statistical method. A narrow interval indicates greater precision than a wide interval, though precision is not the same as freedom from bias. For this study, no confidence interval for a primary endpoint estimate is reported in the registry record. The precision of any group contrast therefore cannot be evaluated.

A p-value, in general, describes how surprising data at least as incompatible with a specified null hypothesis would be under the model assumptions. It does not measure the size or importance of an effect, and it does not establish that groups are equivalent when a result is not statistically significant. No primary endpoint p-value is reported in the registry record, so there is no reported hypothesis-test result to interpret.

How should planning illustrations be read?

The record describes planning illustrations based on an observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The effect to detect is described as a stated fraction of the observed effect. Such calculations are planning scenarios: they ask what participant count might be needed under the chosen assumptions. They are not observed power, and they do not establish that the original study was designed with those assumptions.

The record does not state the trial’s own sample-size justification. Nor does it report the observed effect needed to interpret a planning illustration in context. A planning calculation cannot replace the missing primary estimate or its uncertainty, and it should not be treated as evidence that the study did or did not detect an effect.

Why might over-dispersion matter in general?

General statistical note: over-dispersion occurs when observed variability is greater than a model assumes. If a method assumes less variability than is present, uncertainty may be understated and inferential results can be too optimistic. The record does not report that over-dispersion was assessed or that a particular model requiring such an assessment was used. This concept is therefore general background, not a claim about the analysis in this study.

The record identifies one analysis but does not describe its statistical method, model assumptions, covariates, handling of repeated observations, or checks of model fit. Without those details, the analysis cannot be reproduced or evaluated for whether its assumptions matched the study design and endpoint.

10. Multiplicity, Missing Data and Analysis Populations

The record lists 3 outcome measures and 1 analysis, but it does not explain how outcomes were selected for analysis or how the analysis related to each measure. A count of outcomes and analyses is not enough to determine whether multiple comparisons were made, whether a primary hypothesis was designated before examining data, or whether any adjustment for multiplicity was planned. A multiplicity strategy is not reported in the registry record.

Multiplicity matters in general when several outcomes, time points, groups or contrasts are examined. Testing many questions can increase the chance that at least one result appears notable by chance. Adjustment methods and a prespecified testing hierarchy are possible approaches, but neither is described for this study. It would be inappropriate to assume that multiplicity was or was not handled.

The primary endpoint population excludes 11 participants with incorrectly performed EVH tests, listed as 5 football players, 4 basketball players and 2 swimmers. The record does not report the number analyzed in each group after exclusion, the handling of missing values beyond these exclusions, or whether any participants were excluded from other outcome analyses. It does not describe an intention-to-treat population, a per-protocol population, or another analysis-population definition.

General statistical note: missing measurements can reduce precision, and bias may arise if the chance that a measurement is missing is related to the outcome or participant characteristics. The direction and extent of any such bias depend on why data are missing and how the analysis handles them. The registry record does not report a missing-data method, an assessment of reasons for missingness, or sensitivity analyses. These points remain unknown rather than evidence that a particular bias occurred.

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.

The adverse-event record lists 0 serious adverse events in the football players, swimmers, basketball players and control group. It also lists 0 other adverse events in each of those groups. The corresponding numbers at risk are 44, 47, 26 and 17, respectively, for both event categories.

These are the counts recorded in the registry, not proof that no event occurred outside the record’s definitions, observation period or reporting process. The record does not define the safety follow-up period or provide further detail about how adverse events were collected. Death counts are not reported in the registry record.

Zero recorded events also do not permit a precise estimate of the frequency of uncommon harms. In general, when no events are recorded, the available information still depends on the number observed, duration of observation and completeness of reporting. Here, the registry record does not provide enough detail to characterize those aspects fully. The safety figures should therefore be read as reported counts, not as a guarantee of absence of risk or as a comparison establishing differences between groups.

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

The record documents a completed longitudinal study of high-school athletes and age-matched controls, with enrollment of 134 and a defined primary measure based on FEV1 response to EVH. It also documents that 11 athlete tests were excluded from the primary endpoint analysis because the EVH test was not correctly performed. These details describe the study population and measurement process.

The record does not report the numerical primary endpoint results, a group contrast, or uncertainty around a contrast. It therefore does not establish whether lung-function responses differed between sports groups and controls, whether those responses changed during follow-up, or how large or precise any difference might have been. The absence of reported estimates is not evidence that the groups were the same; it is a limit on what can be concluded from the registry record.

The broader study summary refers to changes in lung function and airway inflammation after 1 and 2 years. However, the record does not provide results for those changes or explain how all repeated measurements were analyzed. The listed secondary outcome concerns the number of participants with allergies determined by a positive skin prick test, but its results are not reported in the registry record.

Interpretation is further constrained by the absence of a stated allocation method, statistical analysis details, missing-data methods and multiplicity plan. The inconsistent descriptions of control-group activity also make the intended comparator unclear. These limitations do not show that the study was conducted improperly; they identify information that is needed to evaluate its findings and their precision.

Accordingly, the record supports a description of the research question, endpoint procedure, exclusions and recorded adverse-event counts. It does not support a conclusion about the presence, absence, magnitude or clinical importance of a difference in lung function or airway inflammation.

13. Why This Trial Matters Statistically

This study is statistically interesting because it combines a longitudinal research question with a challenge-based lung-function endpoint. Repeated follow-up can address how measurements change over time, while an EVH response captures a specific change after a respiratory challenge. These questions require clear definitions of the outcome, time points, comparison groups and analysis population. The registry record defines aspects of the measurement procedure but does not report the results or the analysis details needed to evaluate those choices.

The record also illustrates why the distinction between an endpoint definition and an endpoint result matters. A detailed protocol description can explain what was intended to be measured, including the FEV1 schedule and the criterion for a positive response. It cannot establish the observed distribution or a group difference without numerical outcome results.

The 11 excluded EVH tests raise a practical statistical issue: outcome validity and participant inclusion are connected. Restricting analysis to correctly performed tests may be appropriate for the intended endpoint, but readers also need to know the analyzed population and how exclusions affect interpretation. Those details are not fully reported in the registry record.

Finally, a nonrandomized comparison and an inconsistent control activity description complicate interpretation of group differences. Statistical comparisons can describe observed associations, but without randomized allocation they do not by themselves isolate the effect of sport participation from other differences between groups. The record does not report enough design or analysis detail to evaluate possible confounding.

The study therefore highlights the value of complete reporting: results for the planned endpoint, estimates of uncertainty, analysis methods, handling of missing measurements and clear definitions of comparison groups. Without those elements, readers can understand what was intended but cannot assess the magnitude or precision of the findings.

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.

Several limitations are specific to the information in this record. First, the primary endpoint results are not reported: no group-specific medians or inter-quartile ranges, effect estimate, confidence interval or p-value is available. This prevents quantitative interpretation of the principal outcome.

Second, the control activity description conflicts across the record. The brief summary describes recreational activity of <4 hours/week, whereas the control-group description says >4 hours. The registry record does not clarify which threshold was intended. This makes the comparator less clearly defined.

Third, the primary endpoint analysis excludes 11 athletes because their EVH tests were not correctly performed. The record gives the sport-specific exclusion counts but does not report analyzed group sizes or sensitivity analyses addressing these exclusions. Other missing-data handling is not reported in the registry record.

Fourth, allocation is not stated, and the record notes that the arms are not a like-for-like control comparison. The statistical analysis method, covariate adjustment, handling of repeated observations, multiplicity strategy and sample-size justification are also not reported in the registry record. These omissions limit assessment of bias, precision and reproducibility.

Finally, the study summary describes follow-up after 1 and 2 years, but the posted results do not provide the longitudinal outcome estimates needed to evaluate change over that period. The secondary allergy outcome is named, but its result is not reported in the registry record. The adverse-event counts are available, while the safety observation period and death counts are not reported in the registry record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Longitudinal Follow-up of High School Athletes — NCT02432183.
• Registry record last updated 2024-01-10; status last verified 2023-12.
• Results first posted 2021-02-05.
• 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

NCT02432183 is a completed longitudinal study sponsored by Universitaire Ziekenhuizen KU Leuven. It enrolled 134 participants and lists football players, basketball players, swimmers and an age-matched control group. The study start is recorded as 2012-09 and primary completion as 2015-06.

The primary endpoint is maximal percentage change in FEV1 after EVH, summarized using the median and inter-quartile range. The record says 11 athlete tests were excluded from the primary analysis because the EVH test was not correctly performed. Numerical primary results and group comparisons are not reported in the registry record.

The record lists 3 outcome measures and 1 analysis. It does not report the statistical analysis method, sample-size justification, multiplicity plan or missing-data approach. The control group’s activity threshold is described inconsistently. Serious and other adverse-event counts are 0 for each listed group; death counts are not reported in the registry record.