Assessing Choice in the Employer Setting (ACES) Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Assessing Choice in the Employer Setting (ACES) Study (NCT00808808), a registered phase not stated study. The primary outcome is Overall Vaccination Rate, All Ages.

2. Clinical Question

The study is the Assessing Choice in the Employer Setting (ACES) Study, an observational study sponsored by MedImmune LLC. Its stated focus is the impact of offering intranasal vaccine in the employer setting. The clinical question concerns a combination of vaccine choice and the way the choice was advertised or supported; the choice-plus arm also included additional incentives. Therefore, the arm descriptions represent different sets of offerings, not simply different vaccine products. The registry record does not report results that would establish how vaccination rates differed among these offerings.

3. Trial Design

ACES is recorded as an observational study with status COMPLETED. The registry record gives enrollment as 4411, a start of 2008-09, and primary completion in 2008-11. Its official title describes an observational study assessing the impact of offering intranasal vaccine on influenza vaccination rates in the employer setting. The record does not state how participants or sites were allocated to arms.

Three arms are described. Arm A, Control, offered TIV as usual care with baseline advertisement. Arm B, Choice, offered a choice of TIV or FluMist with baseline advertisement, including advertisement highlighting FluMist availability. Arm C, Choice Plus, offered a choice of TIV or FluMist with enhanced advertisement and additional incentives for receiving an influenza vaccination. The contrast between arms therefore involves both vaccine choice and differences in advertising or incentives.

The stated primary outcome is Overall Vaccination Rate, All Ages, for all employees at participating sites, vaccinated or not. Its timeframe is 30Sep2008 through 23Dec2008. The study summary describes questions about effects among adults and in the total population. The registry also lists secondary outcomes concerning change in vaccination rates from the baseline season to the intervention season in the total population and in employees 18-49 years of age; FluMist choice among eligible participants 18-49 years of age; and race, education, and gender characteristics of participants in that age group choosing FluMist versus TIV.

The registry record lists eight outcome measures and zero analyses. The allocation method, number of participating sites, arm-specific enrollment, and detailed analysis plan are not reported in the registry record. Given the observational designation and the record's warning that the arms are not a like-for-like control comparison, the descriptions do not support treating the arm contrast as a randomized comparison.

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: All employees at participating sites, including those who were vaccinated and those who were not

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 Overall Vaccination Rate, All Ages, measured over 30Sep2008 through 23Dec2008.

The primary outcome is titled Overall Vaccination Rate, All Ages. The registry identifies its unit as percentage of participants and its population as all employees at participating sites, including those vaccinated and those not vaccinated. The outcome timeframe is 30Sep2008 through 23Dec2008. The parameter is recorded as NUMBER, while the title and unit describe a rate expressed as a percentage; the registry record does not clarify this labeling.

A vaccination rate is a binary-outcome summary: each person is classified according to whether the event of interest occurred, and the rate describes the proportion classified as vaccinated in the defined population and timeframe. This general description explains the meaning of a percentage endpoint; it does not establish additional details about how the registry's outcome was derived. The record does not report the exact event definition, denominator handling, or whether any eligibility or data-completeness rules were used.

Rates can describe uptake in an employer population and can be compared across groups or seasons when the populations and measurement procedures are sufficiently clear. The registry lists change from baseline season to intervention season as a secondary outcome, but it does not report the values for either season or the resulting change. No primary outcome rate, arm-specific estimate, uncertainty interval, or statistical test is reported in the registry record. As a result, the endpoint's intended interpretation is clear at a broad level, but its observed value and precision cannot be assessed from the posted results.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The statistical information in the registry record is limited: it lists eight outcome measures and zero analyses. The record does not report statistical tests, model specifications, adjusted estimates, confidence intervals, p-values, or analysis populations beyond the population named for the primary outcome. The concepts below explain how these methods are generally used; they do not imply that ACES used them.

What does a vaccination percentage describe?

In general, a percentage for a binary outcome summarizes how many people in a defined population experienced the event relative to the number assessed. The outcome in ACES is described as an overall vaccination rate, with the unit given as percentage of participants. To interpret such a rate, readers need a clear event definition, denominator, population, and observation period. The registry identifies all employees at participating sites, including those vaccinated and not vaccinated, and gives the timeframe as 30Sep2008 through 23Dec2008. Further operational details about classification and denominator rules are not reported in the registry record.

A percentage alone is descriptive. It does not establish whether a difference between arms is larger than would be expected from sampling variability, nor whether the groups were comparable. For an arm comparison, an analysis would ordinarily define the estimate of interest, such as a difference in rates, and quantify its uncertainty. No such estimates are reported for this study.

What would uncertainty measures add?

In general, a confidence interval communicates the precision of an estimate by giving a range compatible with the observed data under the chosen statistical method. A p-value, when used, describes how unusual data at least as discrepant as those observed would be under a specified null hypothesis and model assumptions. Neither quantity on its own establishes causation or practical importance. The registry record gives no confidence intervals or p-values for the vaccination-rate outcome, so neither precision nor evidence against a null comparison can be evaluated from its posted results.

For a binary outcome, the uncertainty in a rate depends in part on how many participants contribute and how the outcome is distributed. In general, analyses may account for features such as grouping by worksite when observations within a site are related. The record does not report site counts, whether clustering was considered, or whether any adjustment was performed. No such method should be assumed.

Why does the observational design matter?

In general, random allocation can make groups comparable on average, whereas observational allocation can leave differences in participant or site characteristics between groups. Those differences can influence both the offering received and vaccination behavior. Adjustment methods may address measured differences, but they cannot necessarily remove the influence of unmeasured factors. ACES is identified as observational; allocation is not stated, and the registry cautions that the arms are not a like-for-like control comparison. The record does not report covariate adjustment or other methods for addressing group differences. Consequently, the arm descriptions should not be treated as evidence of a randomized, isolated comparison.

The interventions also differ in more than one respect: the choice arm includes vaccine choice and baseline advertisement, while the choice-plus arm includes enhanced advertisement and additional incentives. In general, a comparison between these arms estimates a contrast between the offerings as a whole unless the analysis separately identifies the contribution of each component. The registry record does not report an analysis that separates those components.

How should the planning illustrations be understood?

The stated sample-size assumptions describe planning illustrations computed from an observed effect, rather than the trial's own design. They specify a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is a stated fraction of the observed effect. These are assumptions for illustrative planning, not evidence that the study was designed or conducted using those assumptions. The record does not report a trial-specific sample-size justification or the observed effect on which any illustration is based.

In general, a power calculation estimates the sample size needed to detect a prespecified effect under assumptions about the outcome, significance level, allocation, and analysis. A planning calculation does not describe the power actually achieved in a completed study. The illustrations are not observed power. The record's general note says that time-to-event planning tables give total events, while other planning tables give participants per arm. The primary outcome described for ACES is a vaccination percentage, not a time-to-event outcome; no trial-specific sample-size result is reported.

The registry record also does not report interim analyses, a prespecified analysis plan, or methods used to handle multiple outcomes. The presence of outcome titles does not show that each was analyzed, and the listing of zero analyses offers no inferential results to interpret. Statistical claims about significance, adjustment, or model fit would therefore go beyond the record.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Arm A (Control)", "Arm B (Choice)", "Arm C (Choice Plus)")
n      <- c(4078, 3757, 4387)
events <- c(1696, 1694, 2237)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Arm A (Control)  4078  1696  41.6  40.1  43.1  40.1  43.1  40.1  43.1
ARM  Arm B (Choice)  3757  1694  45.1  43.5  46.7  43.5  46.7  43.5  46.7
ARM  Arm C (Choice Plus)  4387  2237  51.0  49.5  52.5  49.5  52.5  49.5  52.5

11. Multiplicity, Missing Data and Analysis Populations

The registry lists eight outcome measures, including the primary overall vaccination rate and secondary outcomes concerning change from baseline, employees 18-49 years of age, choice of FluMist, and participant characteristics. It records zero analyses. The registry record does not report whether a multiplicity strategy was planned or used, how outcomes were prioritized beyond the primary outcome designation, or whether any subgroup or pairwise comparisons were conducted.

In general, when several hypotheses are tested, the chance of at least one apparently notable result can increase if each test is judged independently. Methods for addressing multiplicity can alter the thresholds for interpretation or otherwise account for the number and structure of comparisons. No specific method can be attributed to this study from the registry record, and there are no posted p-values to interpret in light of multiplicity.

The registry record does not report missing-data amounts, reasons for missingness, or a method for handling incomplete outcome information. It also does not say whether all eligible employees had outcome data, whether exclusions occurred, or whether sensitivity analyses were conducted. These details matter because the percentage may depend on who is included in its denominator. The stated primary population includes employees who were vaccinated and those who were not, but this description does not resolve how unknown or unavailable vaccination status was handled.

Beyond the primary population description, analysis populations are not reported in the registry record. There is no account of whether analyses used all enrolled employees, a subset with complete outcome information, or another defined group. Therefore, the registry record does not permit assessment of missing-data bias, multiplicity control, or consistency across analysis populations.

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

The study record defines a relevant employer-setting question: how vaccination rates relate to offerings that include vaccine choice, advertising, and incentives. It describes a control offering TIV only and two offerings that include a choice of TIV or FluMist. It also identifies an overall vaccination-rate outcome and several secondary outcome topics. These details clarify what the study set out to examine.

They do not establish what happened. The registry record does not report the overall vaccination rate, arm-specific rates, changes from baseline, or estimates comparing the arms. It reports no confidence intervals, p-values, or analyses. As a result, readers cannot determine the direction, size, or precision of any difference from the posted results. The COMPLETED status indicates the recorded study status, not an outcome finding.

The study's observational designation is important to interpretation. Allocation is not stated, and the registry cautions that the arms are not a like-for-like control comparison. General statistical reasoning therefore requires caution: differences in outcomes could reflect differences between groups as well as differences in the offerings. Because the offerings also vary in advertising and incentives, a contrast would not necessarily isolate the effect of vaccine choice alone.

The outcome names also do not establish that analyses were completed. The record lists eight outcome measures and zero analyses, and does not describe missing-data procedures, adjustment methods, or multiplicity handling. The adverse-event fields list zero at-risk and affected values in each arm, with deaths null and no serious-event terms; the record provides no further explanation of those entries.

The defensible interpretation is limited to the study's stated objective, setting, arm descriptions, and outcome definitions. The posted results do not show whether any offering was associated with a higher or lower rate, whether any difference was statistically distinguishable from chance, or whether an estimated effect would be precise. No treatment recommendation follows from these registry entries.

13. Why This Trial Matters Statistically

ACES is statistically interesting because its question involves both the availability of vaccine choice and the way that choice is presented or encouraged. The three arm descriptions distinguish usual care offering TIV only, a choice of TIV or FluMist with baseline advertisement, and a choice with enhanced advertisement and additional incentives. These are policy and implementation bundles, not simply a comparison of two vaccine products. A useful analysis would need to match its estimate to the specific contrast being asked about.

The observational designation makes comparability central. In general, a difference in vaccination percentages between groups can reflect both the intervention offering and pre-existing differences in the people or settings represented in each group. The registry states that allocation is not stated and that the arms are not a like-for-like control comparison. That warning is a substantive limitation on causal interpretation, not merely a technical detail.

The endpoint is a percentage among employees at participating sites, which makes its population and denominator important. The record supplies a broad population definition and timeframe, but does not report the rate itself or explain denominator handling. Without an estimate and uncertainty measure, statistical precision cannot be judged. The record's listing of multiple outcome topics also raises a general need to distinguish prespecified primary questions from additional comparisons, while the multiplicity approach itself is not reported.

Finally, the record illustrates the difference between planning and evidence from completed outcomes. Its sample-size assumptions are described as planning illustrations based on an observed effect, not as the trial's own design, and they are not observed power. Since no outcome analyses are reported, the statistical value of the record lies in clarifying the question and the limits of what can be inferred, rather than in establishing an effect 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 main limitation for interpreting this record is the absence of reported outcome results. Although the primary outcome and several secondary outcome topics are identified, the registry record gives no vaccination percentages, changes from baseline, group contrasts, confidence intervals, or p-values. It lists eight outcome measures and zero analyses. The size and direction of any association, and its precision, cannot be assessed.

The observational design and unspecified allocation further limit causal interpretation. The registry explicitly cautions that the arms are not a like-for-like control comparison. The record does not report whether groups differed at baseline, whether statistical adjustment was used, or how site-level features were handled. These missing details matter when distinguishing an effect of an offering from other differences between employees or participating sites.

The intervention contrasts also combine components. Choice of vaccine, advertisement, and incentives vary across the arm descriptions. Without reported analyses designed to separate components, a contrast between arms would not necessarily isolate the effect of any single element. The record does not report how many sites participated or how many employees were included in each arm, beyond the overall enrollment of 4411.

Outcome measurement and data completeness are not described in sufficient detail for assessment. The registry identifies the all-ages employee population and outcome timeframe but does not report denominator rules, missing-data amounts, missingness reasons, or sensitivity analyses. It also does not clarify the primary outcome labeling, which gives a percentage unit while recording the parameter as NUMBER.

Finally, the record does not report the trial's own sample-size justification, analysis plan, interim analyses, or approach to multiple outcomes. The listed planning assumptions are illustrative and do not replace those details. Adverse-event fields are sparse, with zero at-risk and affected entries, null deaths, and no serious terms listed; further collection and reporting details are not reported in the registry record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Assessing Choice in the Employer Setting (ACES) Study — NCT00808808.
• Registry record last updated 2013-11-20; status last verified 2013-10.
• Results first posted 2012-09-13.
• 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 Assessing Choice in the Employer Setting (ACES) Study, NCT00808808, is recorded as a completed observational study sponsored by MedImmune LLC. Enrollment is 4411. The record gives a start of 2008-09 and primary completion in 2008-11.

Its primary outcome is Overall Vaccination Rate, All Ages, expressed as a percentage of participants among all employees at participating sites, with a timeframe of 30Sep2008 through 23Dec2008. The arms were usual care with TIV only, vaccine choice with baseline advertisement, and vaccine choice with enhanced advertisement and additional incentives. Allocation is not stated, and the registry cautions that the arms are not a like-for-like control comparison.

The registry lists eight outcome measures and zero analyses. It does not report vaccination-rate results, statistical comparisons, or uncertainty estimates. The posted information therefore describes the study question and design features but does not establish the direction, magnitude, or precision of an outcome difference.