Gulf War Illness Nasal Irrigation Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Gulf War Illness Nasal Irrigation Study (NCT01700725), a randomized phase 2 study. The primary outcome is Change in Sino-Nasal Outcome Test (SNOT-20) Score From Baseline.

2. Clinical Question

The clinical question therefore concerns whether adding either irrigation approach to routine care is associated with change in sinus-disease-specific quality of life, relative to routine care alone. The primary outcome description identifies two follow-up time points, but the registry does not provide a single reported comparison that can answer that question. It also lists changes in the Multidimensional Fatigue Inventory and Medical Outcomes Survey Short Form-36 as secondary outcomes. Their outcome results are not reported in the registry record.

3. Trial Design

The registry identifies this as a Phase 2 study with randomized allocation and no masking. It lists enrollment of 40 and a completed status. The study began in 2012-10, with primary completion in 2016-06. The sponsor is the University of Wisconsin, Madison.

Three groups are described: saline irrigation plus routine care, xylitol irrigation plus routine care, and a control group receiving routine care only. The registry's model designation is single-group, while its allocation designation is randomized and its descriptions include three groups. These entries do not align clearly, so the record does not establish how the study was organized beyond the listed group descriptions and allocation label. Details about the randomization procedure, allocation concealment, and the planned statistical comparison are not reported in the registry record.

No masking was recorded. The record does not explain whether participants, clinicians, outcome assessors, or analysts were unmasked, so the masking entry should not be interpreted more broadly than its wording. The interventions are described as nasal irrigation with saline or xylitol, each alongside routine care, while the control continued routine care only.

The primary outcome was change in SNOT-20 score from baseline at week 8 and week 26. The listed secondary outcomes were changes in fatigue measured by the Multidimensional Fatigue Inventory and health-related quality of life measured by the SF-36. The registry record gives no analysis population, statistical model, or description of how the three listed groups were compared. It also does not report a sample-size justification or interim-analysis plan.

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 from one participant in the control group and two participants in the Saline group at 26 weeks was unable to be 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 Change in Sino-Nasal Outcome Test (SNOT-20) Score From Baseline, measured over Change from baseline week 8, change from baseline week 26.

The primary endpoint is change in the Sino-Nasal Outcome Test (SNOT-20) score from baseline, recorded at week 8 and week 26. SNOT-20 is a 20-item questionnaire used to assess sinus-disease-specific quality of life in chronic rhinosinusitis. The registry describes its total score as ranging from 0 to 100; higher scores indicate worse symptoms. A change score expresses how the participant's recorded score differs from baseline, with the direction and size of change interpreted in light of that scale.

The registry describes SNOT-20 as a recommended research outcome and notes that it is intended to capture health burden and be sensitive to clinical change. The listed rationale also describes it as a reliable and valid measure for patients with chronic rhinosinusitis. This makes the endpoint relevant to the sinus symptoms the intervention was intended to address. It does not, by itself, measure fatigue, which is addressed separately among the secondary outcomes.

Change from baseline can help distinguish follow-up status from the starting score, but interpretation requires outcome data and a comparison plan. The registry record identifies two follow-up times without reporting the group means, variability, or statistical contrasts for either time point. It therefore does not show whether scores changed, how precisely any change was estimated, or whether changes differed between groups.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a continuous primary outcome summarized by a mean and standard deviation. General statistical interpretation begins by separating the observed group summaries from the comparison of interest. A mean describes the average change in score among the participants included in a calculation. A standard deviation describes how widely individual changes vary around that mean. Neither measure, by itself, quantifies the uncertainty in a difference between groups.

What would a confidence interval describe?

General explanation: a confidence interval gives a range of values compatible with the data and the statistical method used. For a group contrast, it helps readers judge both the estimated direction and the precision of the result. A narrow interval indicates greater precision than a wide interval, while an interval spanning values in different directions may leave the direction uncertain. The registry record does not report confidence intervals for the primary outcome.

How should a p-value be read?

General explanation: a p-value is a measure of how compatible the data are with a specified null hypothesis under the assumed analysis. It is not the probability that the null hypothesis is true, and it does not measure the size or clinical importance of an effect. A p-value is most informative when read alongside the estimate, its uncertainty, the analysis plan, and the study design. No primary-outcome p-value is reported in the registry record.

Why does the analysis plan matter?

General explanation: a statistical model and comparison plan define which groups are contrasted, how repeated measurements are handled, and which participants contribute to each estimate. With measurements at more than one follow-up time, an analysis might compare changes separately at each time or use a model that accounts for measurements over time. These approaches answer related but not identical questions. The registry identifies week 8 and week 26 but does not report the model or planned comparison.

The record labels allocation as randomized, but it does not describe the sequence-generation method or allocation concealment. General explanation: random allocation can help make groups comparable at baseline on average, but it does not guarantee that all group characteristics are identical, especially in a study of limited size. The validity of an estimate also depends on how participants are analyzed, whether outcomes are missing, and whether the statistical approach matches the design. Here, the registry's single-group model designation sits alongside a randomized allocation label and three group descriptions. This leaves the analysis structure unclear.

What does over-dispersion mean?

General explanation: over-dispersion refers to variability greater than a statistical model assumes. It is most often discussed for count outcomes, where a model may otherwise underestimate uncertainty if the observed counts vary more widely than expected. The primary outcome in this study is a continuous score, not a count, and the registry does not report an analysis where over-dispersion was assessed. The concept is therefore general context rather than a reported feature of this study's analysis.

How should planning calculations be understood?

The record describes sample-size 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. It states that the effect to detect is a stated fraction of the observed effect. These assumptions describe illustrative calculations, not the trial's original design or an observed estimate of power. The registry does not report its sample-size justification. A planning illustration should not be read as observed power or as evidence that a comparison was adequately powered.

General explanation: planning calculations estimate the number of participants that would be needed under chosen assumptions about the target effect, variability, significance threshold, and desired power. If the assumed effect changes, the required sample size can change as well. Such calculations do not show how likely a result from an already completed study was to be significant. The record's planning assumptions therefore need to remain distinct from the study's enrollment and from any observed outcome analysis.

For this study, the central limitation is not a reported statistical finding that needs reinterpretation, but the absence of outcome estimates and their uncertainty in the registry record. Without those results, the endpoint definition and design descriptors cannot be converted into a quantitative treatment comparison.

10. Multiplicity, Missing Data and Analysis Populations

The primary outcome is listed at two time points, week 8 and week 26, and the registry also lists two secondary outcomes: change in the Multidimensional Fatigue Inventory and change in the SF-36. Examining multiple outcomes or time points raises a general multiplicity issue: the more inferential comparisons considered, the greater the chance that an apparently notable result arises by chance if each is assessed separately. A prespecified hierarchy or adjustment can help address this, but the registry record does not report a multiplicity strategy or identify a single primary time point for inference.

The primary outcome entry notes that data from one control participant and two saline participants at 26 weeks could not be collected. It does not state why these data were unavailable, whether other outcome data were missing, or how missing values were handled. The method used to account for missing data, if any, is not reported in the registry record. General explanation: missingness can affect both the amount of information available and the interpretation of a comparison, particularly if the reasons for missingness differ between groups or relate to participants' outcomes.

The registry does not identify whether analyses were based on all randomized participants, participants who completed follow-up, or another analysis population. It also does not describe handling of protocol deviations or withdrawals. Those details matter because different analysis populations can produce estimates answering different questions. Without a reported analysis population, missing-data approach, and outcome estimates, the impact of unavailable observations cannot be evaluated.

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 0% reporting threshold.

For the xylitol group, the registry lists 14 participants at risk for serious adverse events and 0 affected; for other adverse events, it also lists 14 at risk and 0 affected. For the saline group, the corresponding counts are 14 at risk and 0 affected for serious adverse events, and 14 at risk and 0 affected for other adverse events. For the control group, the record lists 12 at risk and 0 affected in each category. Deaths are recorded as 0 in each group.

These figures describe the registry's reported counts in the listed categories. They do not provide details about how events were defined, how actively they were sought, or the duration of safety follow-up. The registry also does not list serious adverse event terms. A count of zero in a category means no affected participants were recorded for that category in the posted results; it does not establish that no symptoms, events outside the categories, or unreported events occurred.

General explanation: safety counts are interpreted in the context of the number of participants observed, the length and completeness of follow-up, and the methods used to collect events. Small counts provide limited information about uncommon outcomes. The registry counts alone do not support a broad conclusion about safety.

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

The record establishes that a Phase 2 study was registered with randomized allocation, no masking, and a stated enrollment of 40. It describes saline and xylitol nasal irrigation alongside routine care, with routine care alone as the listed control. It identifies change in SNOT-20 score at week 8 and week 26 as the primary outcome, and changes in fatigue and SF-36 as secondary outcomes.

Those design and endpoint descriptions clarify the question the study was intended to address. They do not provide the answer to that question. The registry record does not report the primary outcome results, group contrasts, confidence intervals, or p-values. It likewise does not report results for the secondary outcomes. The direction and size of any changes, and the precision of any comparisons, therefore remain unknown from this record.

The safety entries show zero affected participants for the reported serious and other adverse event categories and zero deaths in each listed group. These counts should be interpreted narrowly as recorded events, not as proof that no adverse experiences occurred or that all potential safety questions were resolved.

General explanation: a statistically significant result, if reported, would not on its own establish that a difference is clinically important; a non-significant result would not establish that groups are equivalent. Both interpretations require the estimated effect and its uncertainty, along with an understanding of the analysis plan. Those primary-outcome statistics are not reported in the registry record.

The appropriate reading is therefore descriptive rather than conclusive: the registry records a study question, several intervention groups, an outcome schedule, and selected safety counts, but not an analyzable result for the clinical comparison. The record does not support a claim that either irrigation approach improved or failed to improve symptoms.

13. Why This Trial Matters Statistically

This study is statistically informative as an example of why a registered study's design labels and outcome definitions are not substitutes for reported results. The registry identifies a randomized allocation, yet its model designation is single-group and its arm descriptions list three groups. Readers need clear alignment between design metadata, group structure, and the analysis plan to understand what contrast an estimate represents.

The endpoint also illustrates the distinction between specifying an outcome and reporting an outcome. SNOT-20 is described as a continuous measure of sinus-disease-specific quality of life, and two follow-up times are named. Without group-level summaries and a contrast with uncertainty, however, the outcome definition cannot establish what happened or how precisely any difference was estimated.

Multiple time points and secondary outcomes make clear why a prespecified inferential plan matters. Choices about which comparison is primary, how repeated measurements are handled, and whether multiplicity is addressed affect interpretation. The registry record does not report those choices. It also notes unavailable 26-week data in two groups, underscoring the importance of transparent missing-data methods and analysis populations.

Finally, the safety counts show why event numbers need context. Zero recorded events in listed categories are useful descriptive information, but interpretation also depends on follow-up and ascertainment, which are not reported in the registry record. Together, these features make transparent statistical reporting essential for judging what an individual trial can and cannot establish.

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 record-specific limitations constrain interpretation. The registry lists randomized allocation and no masking but designates the model as single-group while also describing saline, xylitol, and control groups. The record does not clarify this discrepancy or explain the exact comparison structure. It does not report the randomization method, allocation concealment, or a statistical analysis plan.

The primary endpoint is identified at week 8 and week 26, but no SNOT-20 results are reported. The registry also gives no group means, standard deviations, treatment contrasts, confidence intervals, or p-values. Secondary-outcome results for fatigue and SF-36 are likewise not reported. The stated study purpose cannot substitute for observed outcome results.

The primary outcome description says data could not be collected at 26 weeks for one control participant and two saline participants. Reasons for missingness, handling of these observations, and the analysis population are not reported in the registry record. The record does not explain whether other data were unavailable or how withdrawals and protocol deviations were addressed.

The registry does not report a sample-size justification, interim-analysis plan, multiplicity strategy, or which follow-up time was intended to be the main inferential focus. For safety, it records counts but does not describe event definitions, collection procedures, or follow-up duration. These gaps limit assessment of the strength, precision, and completeness of the evidence recorded.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Gulf War Illness Nasal Irrigation Study — NCT01700725.
• Registry record last updated 2019-05-21; status last verified 2019-05.
• Results first posted 2019-05-21.
• 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 Gulf War Illness Nasal Irrigation Study is listed as a completed Phase 2 study sponsored by the University of Wisconsin, Madison, with enrollment of 40. The registry describes randomized allocation and no masking. It lists saline irrigation plus routine care, xylitol irrigation plus routine care, and a control group continuing routine care only, while also carrying a single-group model designation.

The primary outcome was change in SNOT-20 score from baseline at week 8 and week 26. Secondary outcomes were changes in the Multidimensional Fatigue Inventory and SF-36. Outcome analyses are not reported in the registry record. The posted safety counts show zero serious adverse events, zero other adverse events, and zero deaths in each listed group.