Impacts of Clinician-Mediated Report-Back: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Impacts of Clinician-Mediated Report-Back (NCT06074159), a randomized na study. The primary outcome is Knowledge Before and After Report-back Intervention..

2. Clinical Question

The comparison concerns knowledge-score change, not whether participants received exposure results: both groups received personal results, using different modes of report-back. The measure was based on responses to a series of statements about environmental exposures. Responses were recoded for correctness, and each participant’s score represented the fraction of questions answered correctly. Scores were measured before report-back and again at least 2 weeks later, up to a maximum of 6 weeks.

The registry describes a randomized, parallel-group study and identifies clinician-guided report-back as the control group for the reported comparison. The posted group means describe positive average changes in both groups, with a larger reported mean change in the clinician-guided group. The estimated difference and its uncertainty address how distinct those group results are statistically. They do not, by themselves, establish why scores changed or whether any individual participant’s knowledge changed in the same way as the group average.

3. Trial Design

The study, titled “Impacts of Clinician-Mediated Report-Back,” is registered as NCT06074159. Its official title is “Expanding Effective Report-back of Environmental Exposures in Clinic-Based Studies.” The registry lists a randomized allocation, no masking, and a parallel model. The study status is completed. Its listed phase is NA, and its condition is Health Knowledge, Attitudes, Practice. Silent Spring Institute is named as the sponsor.

The two report-back approaches were clinician-guided and self-guided. In the first, participants received their personal exposure results from a clinician; in the second, they received the results through a website. The brief summary describes training clinicians to return personal exposure results in pregnancy cohorts and measuring environmental health literacy outcomes for clinicians and study participants.

The registry lists enrollment of 163. Arm descriptions state that 200 participants receive results in each mode, while the posted primary outcome results report 87 participants for clinician-guided report-back and 75 for self-guided report-back. The registry record does not explain the relationship between the arm-description figures and the analyzed outcome counts. The outcome population also excludes responses when a participant selected “decline to answer” for any knowledge question at either survey, so the outcome counts should not be read as a full accounting of everyone enrolled or assigned.

The registry lists study start as 2023-08-25 and primary completion as 2024-12-20. It describes surveys completed before report-back and at least 2 weeks after report-back, up to a maximum of 6 weeks. Further details about randomization procedures, allocation concealment, recruitment, or the original design assumptions 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.

Before assignment: Only study participants who received personal exposure reports were considered enrolled in the study. Clinicians also took part in the study but were not considered enrolled.

Overall Study

Analysis population for the primary outcome, as defined in the registry: Participant responses were excluded if they selected "decline to answer" for any knowledge question at either 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 Knowledge Before and After Report-back Intervention., measured over Participants completed pre and post-surveys before and at least 2 weeks after report-back up to a maximum of 6 weeks..

The primary endpoint is the change in participants’ knowledge scores before and after report-back. Participants answered a series of 9-11 statements about environmental exposures, choosing among true, probably true, probably false, or false. Responses were recoded to indicate correctness, and an index score was calculated as the fraction of questions answered correctly. The score ranges from 0-1.

The registry says pre-survey scores were subtracted from post-survey scores to obtain the reported change. It also states that a larger mean change indicates a larger knowledge gain. The posted means are therefore interpreted as average changes in the score, rather than as the average knowledge score at a single survey occasion. The unit is scores on a scale, and the reported summary measure is the mean with standard deviation.

This endpoint is useful for comparing how knowledge scores changed after two report-back approaches. Comparing change scores focuses on the before-to-after movement rather than only the post-survey level. It does not directly measure whether a participant acted on the results, whether knowledge was retained beyond the stated follow-up window, or whether clinicians’ environmental health literacy changed. The registry lists five outcome measures, but secondary outcome results are not posted in the record. The exact content of the knowledge statements and further details about the scoring rules are not reported in the registry record.

7. Results Posted in the Registry

• Self-guided Report-back: mean 0.02 versus 0.06 on control; difference -0.04 (95% CI -0.09 to 0.01), standardized effect d = -0.27; z-test p = 0.093.

8. Statistical Interpretation

9. Statistical Methods Explained

The outcome is continuous: each participant has a knowledge index based on the fraction of correct responses, and the primary summary is the mean change. A mean describes the average score change in a group. It does not imply that every participant changed by that amount. The standard deviation describes how spread out individual change scores are around the group mean. It is a measure of variability among participants, not a measure of the precision of the mean itself.

What does the mean difference compare?

The comparison uses clinician-guided report-back as the reference group and expresses the self-guided group relative to it. The reported mean difference is -0.04. In plain language, the average change score was lower in the self-guided group by the amount represented by that estimate. The sign depends on the order of subtraction; reversing the order would reverse the sign without changing the underlying contrast. The estimate is an absolute difference on the knowledge-score scale, not a relative percentage change.

The posted group means are 0.06 and 0.02, and the reported standard deviations are 0.14 and 0.16. The comparison also includes a pooled standard deviation and a standardized effect estimate. These are ways of describing the contrast relative to score variability. They do not replace the original-scale mean difference, and the registry’s reported outcome remains a change in scores on a 0-1 scale. Since the standardized estimate is not needed to interpret the original-scale contrast, the score-scale difference and its uncertainty are the clearest quantities for understanding the primary result.

What does the p-value tell the reader?

The reported p-value is unadjusted and equals 0.093. General explanation: a p-value is calculated under a statistical model that assumes a null difference, and it describes how unusual a result at least as discrepant as the observed result would be under that model. It is not a measure of the probability that the observed difference occurred by chance, and it does not measure the probability that either report-back approach is better. The unadjusted value does not account for multiplicity, and the registry record does not describe whether or how any multiplicity adjustment was planned.

A threshold such as 0.05 is a convention for decision-making, not a boundary between a true and false effect. The estimate and its confidence interval retain meaning regardless of whether the p-value crosses such a threshold. Here, the interval spans zero and the p-value is 0.093; both features indicate that the data do not sharply distinguish the estimated contrast from no difference under the reported unadjusted comparison.

Why does variability matter?

General explanation: greater variation among individual outcomes makes a group mean harder to estimate precisely if other features of the study are unchanged. A broad spread of individual changes can coexist with different group means, but it can also make it difficult to tell whether a mean contrast is distinguishable from random variation. The standard deviations in the two groups describe this individual-level spread. The standard error describes uncertainty in an estimated group mean, and the registry’s recalculated standard errors are 0.015 and 0.018. Standard deviations and standard errors answer different questions: one describes participant-to-participant spread, the other the sampling uncertainty of a mean estimate.

General explanation: over-dispersion matters when outcome variability exceeds what a statistical model assumes. A model that understates variability can produce standard errors that are too small and intervals that are too narrow. This outcome is a continuous score, and the record does not report an over-dispersion assessment or a model-based adjustment for it. The issue is therefore a general statistical consideration, not a reported finding of this trial.

How should the recalculated comparison be understood?

The recalculated comparison is an unadjusted calculation from the posted summary statistics. It contrasts the two group means without adjustment for baseline scores or other participant characteristics. It is not a reconstruction of an unreported prespecified model. The record marks no discrepancy between the recalculation and sponsor results; where a discrepancy is identified in a record, the sponsor’s own analysis takes precedence. Here, no such discrepancy is flagged.

The reported comparison relies on the available change-score summaries and does not show how missing survey responses were handled beyond the stated exclusion rule. A change-score comparison can be affected by baseline differences, measurement variability, and who contributes follow-up data. The registry record does not report adjusted results or further analysis details, so those features cannot be assessed from the posted result. These limitations concern interpretation of the estimate and do not alter its reported numerical value.

10. Confidence Intervals and Precision

The estimated mean difference was -0.04, comparing self-guided with clinician-guided report-back. The confidence interval extends from a negative value to a positive value, so it includes zero. This means the result is compatible with a lower average change for self-guided report-back, no mean difference, or a higher average change for self-guided report-back. The interval is therefore not precise enough to settle the direction of the population contrast.

A confidence interval is a range of values compatible with the observed data under the statistical method used. General explanation: if the same design and method were repeated many times, intervals constructed in this way would cover the true parameter at the stated confidence level at the corresponding long-run rate. A confidence interval is not a range containing a specified proportion of individual participants’ scores, and it is not a probability statement about the particular fixed effect.

The group standard deviations, 0.14 and 0.16, describe spread among individual changes, while the confidence interval describes uncertainty about the mean difference. The reported standard errors for the group means are 0.015 and 0.018. These summaries are related but not interchangeable. The interval’s span across zero, together with the unadjusted p-value of 0.093, indicates uncertainty about the direction and magnitude of the contrast. The registry record does not report an adjusted interval, a prespecified confidence level, or a model accounting for baseline values and other covariates. The interval should therefore be interpreted as belonging to the posted unadjusted comparison, rather than as a fully adjusted estimate.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning illustrations give participants per arm for 80% power and participants per arm for 90% power. They are based on the observed effect and are not observed power. The calculation assumes a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. Each planning scenario uses the stated fraction of the observed effect as the effect to detect. The figures are planning illustrations, not the trial’s original enrollment target or a claim about the study’s achieved power.

For planning at 100% of the observed effect, the illustration gives 220 participants per arm for 80% power and 294 participants per arm for 90% power. At 75% of the observed effect, it gives 391 participants per arm for 80% power and 523 participants per arm for 90% power. At 50% of the observed effect, it gives 879 participants per arm for 80% power and 1,176 participants per arm for 90% power. These are alternative planning scenarios, not observed trial group sizes.

In plain language, 80% power means that under the calculation’s assumptions, a study of the stated size would have an 80% chance of detecting an effect of the specified size using the assumed test. The 90% column describes the corresponding planning target for a 90% chance. Higher power generally requires a larger sample when other assumptions are held constant. Smaller effects are harder to distinguish from random variation, so planning to detect a smaller effect requires more participants. The registry’s own original sample-size assumptions are not reported in the registry record.

12. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -0.040; pooled standard deviation σ = 0.150.
2. n = 2 × (1.96 + 0.842)² × 0.150² / -0.040² = 219.5, rounded up to 220 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- -0.04                      # observed difference in means
sigma <- 0.149582753016516                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(6074159)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 220 (80% power), 294 (90% power)
 75% of observed effect: n per arm = 391 (80% power), 523 (90% power)
 50% of observed effect: n per arm = 879 (80% power), 1,176 (90% power)
power.t.test: 220.5 
Simulated power at n = 220 per arm: 0.802 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Multiplicity, Missing Data and Analysis Populations

The registry lists five outcome measures, but it posts no secondary outcome results. It does not report how many hypotheses were planned, which outcomes were designated primary in an analysis plan, or whether a multiplicity procedure was specified. When several outcomes or comparisons are examined, the chance of at least one apparently unusual result can increase. General explanation: multiplicity methods adjust interpretation or testing to account for a family of comparisons. Whether such an adjustment is relevant cannot be determined from the registry record.

The reported p-value is unadjusted. It should not be treated as multiplicity-adjusted, and no correction should be inferred. The registry lists zero analysis entries, and details of any analysis plan, interim analyses, or prespecified model are not reported in the registry record. The posted result therefore does not establish whether the reported comparison was the only analysis considered.

For the knowledge endpoint, responses were excluded if participants selected “decline to answer” for any knowledge question at either survey. The registry does not report how many participants met this exclusion, how many lacked a survey for another reason, or how missing item responses were handled beyond that rule. The primary outcome counts are 87 for clinician-guided report-back and 75 for self-guided report-back, but the record does not provide a participant flow accounting for those counts.

The record also does not state whether the analysis followed an intention-to-treat principle, whether participants were analyzed according to assigned mode, or whether another analysis population was used. No imputation method, sensitivity analysis for missing outcomes, or adjusted analysis is reported. Consequently, the posted estimates describe the reported outcome groups, but the extent to which missingness or analysis-population choices could affect them cannot be assessed.

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

The posted results describe positive average knowledge-score changes in both report-back groups: 0.06 for clinician-guided report-back and 0.02 for self-guided report-back. The estimated contrast is -0.04 for self-guided relative to clinician-guided report-back. This is a descriptive and statistical comparison of average change scores in the participants included in the posted outcome summaries.

The result does not establish that one mode caused a larger change. Randomized allocation is part of the study design, but the registry record does not provide enough detail about allocation procedures, missing outcomes, analysis populations, or adjusted analyses to resolve every potential source of uncertainty. The unadjusted p-value is 0.093, and the confidence interval spans zero; the result is compatible with differences in either direction as well as no mean difference.

The outcome is a survey-based knowledge index. It does not directly measure behavior, clinical decisions, health outcomes, exposure reduction, or long-term retention of information. The follow-up survey occurred at least 2 weeks after report-back and no later than 6 weeks, so the result concerns the stated short follow-up window. The registry does not report whether the score’s questions were validated, how participants interpreted the statements, or whether knowledge changes persisted later.

Group means also do not describe every participant’s response. The standard deviations of 0.14 and 0.16 indicate individual variability around the group means. Some participants may have had larger changes, smaller changes, or changes in the opposite direction; individual-level results are not reported. Nor does the result show whether clinician training or the report-back content itself contributed to the observed scores.

The appropriate reading is limited: the registry reports a modestly higher mean change in the clinician-guided group, with uncertainty that includes no difference and a higher change in the self-guided group. These findings should not be translated into medical advice or a claim that either report-back mode works or does not work.

15. Why This Trial Matters Statistically

This trial raises a useful statistical question about how to compare two ways of returning environmental exposure results when the outcome is measured before and after the intervention. The endpoint is a change score on a bounded index, and its interpretation depends on both the average change and the variability of individual changes. Looking only at the group means would leave out the uncertainty around the contrast; looking only at a p-value would leave out the size and direction of the estimate.

The record illustrates why confidence intervals matter. The mean difference is -0.04, while the interval spans zero. That combination communicates both the direction of the point estimate and the fact that a range of possible contrasts remains compatible with the data. It avoids treating a threshold as a dividing line between a conclusive and inconclusive result.

The study also illustrates the difference between an observed result and planning assumptions. The posted enrollment and outcome counts describe the trial record; the larger sample-size figures are hypothetical planning illustrations based on fractions of the observed effect. They are not evidence that the study had or lacked a particular achieved power. Smaller effects require larger planned samples under the stated assumptions, which makes the choice of a meaningful effect size central to future planning.

Finally, transparency about exclusions and analysis populations matters. The record states an exclusion rule for declined survey responses but does not give a full accounting of missing data or the analysis population. Those details help readers judge how well the analysis represents the randomized groups and how robust a comparison may be. Their absence is an interpretive limitation, not evidence that the results are biased in a particular direction.

16. 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 most direct limitation is uncertainty around the estimated contrast. The mean difference is -0.04, the unadjusted p-value is 0.093, and the confidence interval spans zero. The result therefore does not sharply distinguish among a lower, similar, or higher mean change for self-guided report-back. The group standard deviations also indicate variability in individual change scores, while individual-level distributions are not reported.

The registry record does not explain the relationship between arm descriptions stating 200 participants in each mode and the posted primary-outcome counts of 87 and 75. Enrollment is listed as 163, but the record does not include a flow accounting that links enrollment, allocation, survey completion, exclusions, and the analyzed counts. The stated rule excluding participants who declined any knowledge item may also mean that the posted outcome summaries represent a selected subset; the number excluded and the effects of exclusion are not reported.

Other details that would support fuller assessment are not reported in the registry record: the original sample-size assumptions, randomization procedures, allocation concealment, prespecified analysis plan, missing-data methods, analysis population, baseline score distributions, adjusted estimates, and multiplicity approach. The record does not report secondary outcome results, despite listing five outcome measures. It also does not provide information on the content or validation of the knowledge questions or longer-term follow-up beyond the stated survey window.

Adverse-event group records list zero participants at risk for serious events, other events, and deaths in both groups, with zero associated events. Because the listed at-risk counts are zero, these entries do not provide a meaningful comparison of event risk between groups. The record’s adverse-event entries should not be interpreted as evidence that no events occurred among participants.

17. Related Tutorials

18. Related Statistical Calculators

19. Sources

• ClinicalTrials.gov: Impacts of Clinician-Mediated Report-Back — NCT06074159.
• Registry record last updated 2026-04-24; status last verified 2025-05.
• Results first posted 2026-04-24.
• 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.

20. Record Summary

NCT06074159 is a completed randomized, unmasked, parallel-group study sponsored by Silent Spring Institute. It compares clinician-guided report-back of personal environmental exposure results with self-guided online report-back. The primary outcome is the change in a knowledge index, based on the fraction of environmental-exposure questions answered correctly before and after report-back.

The posted mean changes are 0.06 for clinician-guided report-back and 0.02 for self-guided report-back. The unadjusted mean difference for self-guided relative to clinician-guided report-back is -0.04, with p = 0.093 and a confidence interval that spans zero. The registry lists enrollment of 163 and outcome counts of 87 and 75; it does not explain the relationship between those counts and arm descriptions of 200 participants per mode.

Secondary outcome results, analysis-plan details, and a complete missing-data accounting are not reported in the registry record. The result is an uncertain comparison of average short-term knowledge-score changes, not a direct measure of behavior or health outcomes.