Gulf War Era Cohort and Biorepository: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Gulf War Era Cohort and Biorepository (NCT01803854), a registered phase not stated study. The primary outcome is VHA Health Care Utilization.

2. Clinical Question

This is a descriptive question about a cohort, not a randomized treatment comparison. The registry record describes collection of epidemiological, survey, clinical, and environmental exposure data, together with blood samples, from Gulf War Era Veterans. Its primary outcome concerns reported use of VHA health care; the record does not report an estimated rate or an analysis comparing groups.

The focus is therefore on describing cohort participation and the stated health care utilization measure, rather than estimating a causal effect. The registry does not report the number classified as VHA users, the number classified as non-users, or an analysis addressing the unanswered survey items.

3. Trial Design

The Gulf War Era Cohort and Biorepository is identified as a pilot study, with the official title CSP # 585 - Pilot Study: Gulf War Era Cohort and Biorepository. The sponsor is the VA Office of Research and Development. The record lists 1275 enrolled participants and an active, not recruiting status. The recorded start date is 2014-09-02, and the primary completion date is 2019-07-21.

The project collected epidemiological, survey, clinical, and environmental exposure information from Veterans who served during the 1990-1991 Gulf War Era. The cohort description specifies that participants signed consent forms, completed a survey, and provided a blood sample. The stated purpose of the resulting data and samples is to enable approved researchers to conduct future research about Gulf War Era Veterans' health.

The pilot also assessed recruitment response and processes. The summary says that this work identified opportunities for improvement, after which CSP 585 activities transitioned to a qualitative phase focused more on the Veteran voice. Staff spoke with Veterans through focus groups, interviews, events, meetings, and other activities to learn about experiences and ideas relevant to this and other Gulf War research projects. The record says this phase provided information that can help researchers develop recruitment processes for future projects.

No randomized allocation is described, and no treatment or control arms are listed. The registry explicitly cautions that this is not a randomized comparison and that the arms are not a like-for-like control comparison. Accordingly, the cohort design supports description of participants and their recorded information; it does not, from the information reported, support interpreting a difference between assigned interventions.

The registry lists two outcome measures, including the primary VHA Health Care Utilization measure. It reports no analyses. Details about the other outcome measure, the protocol, recruitment targets, and the sample-size justification 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

Analysis population for the primary outcome, as defined in the registry: Twelve participants did not respond to the survey questions used to determine VHA user status.

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 VHA Health Care Utilization, measured over 20 months.

The primary outcome is titled VHA Health Care Utilization. It is described as use of VHA for health care in the past year, with the unit listed as participants and the outcome type described as a count of participants. In practical terms, the measure concerns how many cohort participants are identified as VHA users, rather than how often each person used care, the cost of care, or a clinical outcome.

The registry lists a 20 months timeframe while describing the measure as use in the past year. The relationship between that timeframe and the survey question is not further explained in the registry record, so the measure should be interpreted using the wording as recorded rather than by assuming a different measurement window.

The record does not state why this endpoint was selected or identify a decision rule based on its value. In general, a health care utilization measure can describe whether members of a defined population report using a health care system. Such a measure can characterize service use, but it does not by itself explain why care was used, assess the quality of care, or establish a health benefit or harm. Those interpretations require information and analyses beyond a count of participants classified by user status.

Twelve participants did not respond to the survey questions used to determine VHA user status. The registry does not report how their missing responses were handled or give the number classified as users among respondents. Consequently, no utilization count or proportion can be inferred from the enrollment total alone.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a cohort with a count outcome, not a randomized comparison. Understanding the statistical language requires separating the way the outcome is defined from the analysis that would be needed to estimate it. The record names VHA Health Care Utilization as the primary outcome, defines it as use of VHA for health care in the past year, and gives participants as the unit. It does not report an analysis or a numerical result.

What does a count of participants represent?

The endpoint concerns a participant classification: user status is determined from survey questions, and the outcome type is described as a count of participants. In general, a count gives the number of people meeting a stated definition. A count is not the same as a percentage, a rate over person-time, or a measure of how frequently each person received care. To interpret a count as a proportion, the relevant denominator and handling of participants without a known status must also be clear. The registry notes twelve nonresponses but does not report the classified count, the denominator used in an analysis, or a missing-data method.

The listed timeframe is 20 months, while the outcome description refers to use in the past year. Because the registry does not explain how those descriptions relate, the measurement window cannot be clarified further from the record. Statistical interpretation should preserve this distinction rather than silently treating the two descriptions as interchangeable.

What would an estimate and confidence interval add?

In general, an estimate is a numerical summary of the quantity being studied. A confidence interval describes uncertainty around an estimate under a specified statistical model and procedure. It helps readers distinguish a precise estimate from one with substantial uncertainty. Neither an estimate nor a confidence interval for VHA utilization is reported in the registry record, so there is no basis for describing the magnitude or precision of a utilization finding.

A test of a hypothesis can address whether data are compatible with a specified null model, given its assumptions. A p-value is not a measure of effect size, clinical importance, or the probability that a hypothesis is true. No p-value or hypothesis test is reported for the primary outcome. More fundamentally, the absence of a randomized comparator means a treatment-effect test is not indicated by the design described in the record.

How should the planning assumptions be read?

The registry includes general sample-size assumptions for an illustration: a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and a target effect stated as a fraction of the observed effect. The record describes such calculations as planning illustrations based on an observed effect, not as the study's own design. Those assumptions do not establish that the cohort was randomized or divided into two assigned groups. The registry does not report an observed effect estimate or sample-size justification. Accordingly, a planning calculation should not be presented as an observed result or as observed power.

In general, power is a design quantity describing the chance that a specified statistical procedure detects an effect of a specified size under assumed conditions. It depends on the assumed effect, variability, design, and analysis. A planning illustration does not show the chance that the completed study found a true effect, and it does not substitute for a reported estimate and its uncertainty. No calculated sample-size values are reported in the registry record.

Why do outcome type and dispersion matter?

General statistical methods for counts depend on how the count arises. A count of people classified into a category differs from a count of repeated events, and the appropriate model depends on the design and distribution. Over-dispersion, in general, means that count variability is greater than a chosen model expects; ignoring it can make uncertainty estimates too small. The registry identifies this outcome as a count of participants, does not report a dispersion value, and does not report a fitted model. There is therefore no basis to claim that a particular count model or dispersion adjustment was used.

For a binary classification summarized as a count, a direct description could report the number with known user status and the number classified as users. A proportion could also be considered if its denominator and missing-response handling were stated. These are general options, not analyses reported for this cohort. The record does not state whether adjustment for other variables was planned or performed.

What can the record establish about the analysis?

The registry reports two outcome measures and no analyses. It does not report model specifications, covariates, confidence intervals, hypothesis tests, interim analyses, or an analysis population beyond the described cohort membership. No statistical plan is reported in the registry record. These omissions mean that the outcome definition can be described, but the analytic approach and inferential result cannot be reconstructed from the record.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists two outcome measures and identifies VHA Health Care Utilization as the primary measure. The other outcome measure and its details are not reported in the registry record. No analyses are reported. The record does not state whether multiple outcomes were tested, whether any multiplicity adjustment was planned, or how outcome priority was handled beyond identifying the primary measure.

In general, when several outcomes or hypotheses are tested, the chance of at least one apparently notable result can increase if each is assessed without accounting for the set of tests. Methods that address multiplicity can control or describe that issue, but the appropriate approach depends on the planned questions and analysis. Since no tests or results are reported, there is no multiplicity-adjusted finding to interpret here, and no adjustment method should be assumed.

The registry specifically notes that twelve participants did not respond to the survey questions used to determine VHA user status. It does not say whether those responses were treated as missing, excluded from an analysis, imputed, or otherwise handled. It also does not report whether the nonresponse affected other outcomes. The user-status denominator and any comparison of respondents with nonrespondents are not reported in the registry record.

In general, missing data can affect an estimate when the people with missing responses differ in relevant ways from those with observed responses. The direction and magnitude of any effect depend on the data and the assumptions used; they cannot be determined from the nonresponse count alone. A complete-case approach, imputation, or sensitivity analysis would each require explicit details to interpret. None is described in the registry record.

The cohort description defines inclusion by consent, survey completion, and provision of a blood sample. The registry does not separately define an analysis population for the primary outcome or specify how cohort membership relates to the twelve unanswered user-status items. No further analysis-population rules are reported.

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 Gulf War Era Veterans group, the registry lists 1275 participants at risk for serious events and 1275 at risk for other events. It records zero participants affected by serious events, zero affected by other events, and zero deaths. No serious adverse event terms are listed.

These figures should be read as the safety counts recorded in the registry, not as a comparison between treatments. The record lists a single group and no randomized allocation or control group. It does not report a comparative risk estimate, confidence interval, or analysis of events. It also does not provide further detail about event definitions or the follow-up period used for the safety counts.

A recorded zero does not establish that the underlying risk is zero. In general, the interpretation of a zero count depends on how events were defined, how completely they were collected, the amount of observation, and the population being monitored. The registry figures establish only that the posted counts are zero for the listed categories; they do not establish the absence of all possible harms or risks.

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

The record documents a pilot cohort and biorepository project involving Veterans who served during the 1990-1991 Gulf War Era. It reports enrollment of 1275 participants and describes collection of survey, clinical, epidemiological, environmental exposure, and blood-sample information. The primary outcome concerns VHA health care use, but the registry does not report the number of participants classified as users or an analysis of that outcome.

Consequently, the record does not establish a utilization rate, a difference between groups, or a relationship between VHA use and any exposure or health condition. It does not support a conclusion about an intervention's effect, because no assigned intervention or like-for-like control group is described. It also does not establish that the outcome is precisely estimated: no estimate or uncertainty interval is reported.

The project has a broader stated purpose than reporting a clinical endpoint. Its collected data and samples are intended for use by approved researchers in future studies of Gulf War Era Veterans' health. The registry summary also describes a transition to qualitative work, including focus groups and interviews, after recruitment processes were assessed and opportunities for improvement were identified. These activities are described as a way to learn from Veterans' experiences and ideas and to inform future recruitment processes.

That description does not quantify the recruitment response rate or specify the improvements identified. The registry does not report qualitative findings, participant quotations, or an analysis of those activities. Such details should not be inferred from the statement that the work generated information useful for future recruitment.

The appropriate interpretation is therefore limited but meaningful: the record documents the cohort's intended data resource, its recruitment and qualitative aims, the primary utilization measure, and the counts posted for safety. It does not report results that answer how many participants used VHA or support causal or comparative conclusions. Future research using the cohort or samples would require its own defined question, methods, and analysis.

13. Why This Trial Matters Statistically

This record illustrates why study design and statistical interpretation must be read together. The primary outcome is a count of participants identified through survey questions, while the project itself is a cohort and biorepository pilot rather than a randomized treatment comparison. Treating it as if it were a controlled trial would misstate what the design can answer.

It also shows why enrollment totals should not be substituted for endpoint results. The record lists 1275 enrolled participants, but notes that twelve participants did not respond to the questions used to determine VHA user status. Without a reported user count, analysis denominator, and missing-data approach, enrollment alone cannot establish an outcome rate.

The project connects statistical data collection with recruitment practice. The pilot assessed recruitment response and processes, and its activities transitioned toward qualitative engagement with Veterans after opportunities for improvement were identified. The registry describes this as a source of information for future recruitment processes, but does not quantify response or publish the findings from those qualitative activities. That distinction matters: a study can have a stated learning purpose without reporting a numerical effectiveness estimate.

Finally, the record separates a research resource from a completed inferential analysis. Data and blood samples are intended for future approved research, while the registry reports no analyses for the listed outcomes. Readers can understand the cohort's purpose, outcome definition, and recorded safety counts, but should not treat planned future use, sample-size illustrations, or zero event counts as evidence of a treatment effect or definitive risk estimate.

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 primary limitation for interpreting the clinical outcome is that no utilization result or analysis is reported. The registry identifies use of VHA for health care in the past year as the outcome and gives a 20 months timeframe, but does not explain their relationship. It also does not report a user count, denominator, estimate, confidence interval, or analysis method.

The registry notes twelve unanswered survey responses relevant to user status but does not describe how they were handled. Because the analysis denominator and missing-data approach are not reported, the extent to which those responses affect interpretation cannot be assessed. The record also does not report the number of respondents classified as users or non-users.

The cohort has no described randomized allocation or like-for-like control group. Any descriptive outcome from the cohort would not, on its own, show that a particular exposure or service caused the observed status. The record does not provide a comparative design or causal analysis.

The cohort definition requires consent, survey completion, and a blood sample. Participation based on those requirements may limit how directly the cohort describes Veterans who did not participate; the size and direction of any such difference are not reported in the registry record. The record says recruitment processes were assessed and opportunities for improvement identified, but it does not report response-rate values or further detail about those opportunities.

Other limitations include the absence of reported analytic methods, statistical plan, sample-size justification, and findings from the qualitative phase. The record lists two outcomes but does not identify the other measure's details. Safety counts are posted without further event definitions, follow-up detail, or a comparison group. These omissions constrain the conclusions that can be drawn from the registry information.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Gulf War Era Cohort and Biorepository — NCT01803854.
• Registry record last updated 2026-09-15; status last verified 2026-08.
• Results first posted 2021-12-02.
• 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

NCT01803854 is the Gulf War Era Cohort and Biorepository, a pilot study sponsored by the VA Office of Research and Development. The record lists enrollment of 1275, a start date of 2014-09-02, a primary completion date of 2019-07-21, and active, not recruiting status.

The cohort includes Veterans who served in the uniformed services during 1990-1991 and signed consent forms, completed a survey, and provided a blood sample. The project collected epidemiological, survey, clinical, and environmental exposure data. Its primary outcome is VHA Health Care Utilization, described as use of VHA for health care in the past year, with a listed timeframe of 20 months. Twelve participants did not respond to the survey questions used to determine user status.

The registry lists two outcome measures and no analyses. It reports zero serious events, zero other events, and zero deaths among the Gulf War Era Veterans group. The project summary also describes a qualitative phase focused on Veterans' experiences and ideas about research and recruitment. Outcome estimates, statistical methods, and further safety details are not reported in the registry record.