Using Attentional Bias Modification to Address Trauma Symptoms: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Using Attentional Bias Modification to Address Trauma Symptoms (NCT02615717), a randomized na study. The primary outcome is Clinician-Administered PTSD Scale (CAPS-5).

2. Clinical Question

The registry rationale is that threat-related attentional biases may be involved in the onset or maintenance of PTSD, and that Attention Bias Modification has been used to address such biases in adults diagnosed with PTSD. It also notes that the approach had not been examined specifically among victims of sexual assaults. Those statements describe the motivation for the study; they are not evidence of an effect in this trial.

The stated purpose also includes examining PTSD symptom clusters and outcomes such as anxiety and depression. The listed secondary measures are the PTSD Checklist (PCL-5), Patient Health Questionnaire (PHQ-9), and Beck Anxiety Inventory (BAI). Results for those measures are not reported in the registry record.

3. Trial Design

The registry classifies the study as randomized, double-masked, and parallel. Randomization means that assignment to the two conditions was intended to be determined by chance; the registry record does not report the sequence-generation method or how assignments were concealed. Double masking is recorded, but the identities of the masked parties and the practical masking procedures are not reported in the registry record. The parallel design indicates that the two conditions were compared as separate groups rather than as a crossover sequence.

The arms are Attentional Bias Modification and the Attentional Control Condition. Both descriptions refer to four 20-minute in-lab sessions across two weeks. The intervention description includes presentation of a fixation cross for 500 ms, followed by a word pair, but the remainder of the intervention description is incomplete. The control description also begins to describe a fixation cross and word pair; its full task details are not reported in the registry record. No additional treatment or follow-up schedule is reported.

The study is marked completed. Its start is recorded as 2015-11 and primary completion as 2016-04. The phase is listed as NA. The sponsor is University of Nebraska Lincoln. The enrollment field lists 6, whereas the brief summary says participants are 20 undergraduate women. The registry record does not reconcile these entries, and it does not state whether either figure refers to a planned or analyzed population.

For the primary outcome, the posted arm summaries list 3 participants in each condition. These group summaries are not, by themselves, a complete account of the analysis population. Whether all randomized participants contributed to the outcome, whether any participants were excluded, and whether an intention-to-treat or another analysis population was used are not reported in the registry record. The registry lists 0 analyses, and it does not report a statistical analysis plan or a formal comparison for the primary outcome.

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

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 Clinician-Administered PTSD Scale (CAPS-5), measured over within three days.

The primary endpoint is the Clinician-Administered PTSD Scale (CAPS-5), reported as a mean total score in units on a scale. The registry describes it as assessing PTSD symptoms and severity. It states that subscales are summed to produce the total score and that the subscales represent different facets of PTSD. The stated score range is 0-80, with higher values indicating higher severity.

A total score provides a single continuous measure for describing the overall symptom burden captured by the instrument. For a randomized comparison, the key statistical question would be whether the outcome distributions or average scores differ between the assigned conditions, while accounting for the uncertainty in the estimates. A mean is a measure of the group’s average score; the standard deviation describes variation among the scores around that average. Neither summary alone establishes whether an observed difference is compatible with chance variation or estimates the precision of a between-group effect.

The registry lists the CAPS-5 timeframe as within three days. The specific reference point for that timeframe, such as the timing relative to the final session, is not reported in the registry record. The instrument is described as a PTSD severity measure, but no clinically meaningful threshold, responder definition, or interpretation of a particular change in score is reported.

The posted results give a mean and standard deviation for each arm, but the registry indicates that values are missing or not estimable for a two-arm comparison of this continuous endpoint. Consequently, the group summaries do not provide a reported effect estimate with uncertainty for the primary contrast.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry record contains descriptive summaries for a continuous outcome but no reported inferential comparison between the two randomized arms. Understanding what such a comparison would ordinarily represent helps distinguish the posted group summaries from a treatment-effect estimate. The explanations below are general statistical concepts; they do not describe an analysis confirmed to have been used in this trial.

What do the mean and standard deviation describe?

For a continuous outcome, the mean is the arithmetic average of the observed scores in a group. It gives a measure of the group’s central level, but it does not describe how evenly scores are distributed around that level. The standard deviation summarizes the degree of spread around the mean. A larger standard deviation indicates more variability among observations, though it does not identify the shape of the distribution or explain why participants’ scores differ.

The CAPS-5 summaries are means and standard deviations, as specified in the registry. They are descriptive statistics for the reported arm summaries. Comparing two means informally is not equivalent to conducting a statistical test: a formal comparison also depends on the uncertainty around the contrast, the sample sizes used in the analysis, and the assumptions or model underlying the calculation.

What would a confidence interval add?

In general, a confidence interval gives a range of values compatible with the data and the method used to calculate it. For a between-arm effect, an interval would help convey precision: a narrower interval indicates less statistical uncertainty under the method, while a wider interval indicates more uncertainty. A confidence interval does not guarantee that the true effect falls inside the particular interval, and its interpretation depends on the statistical procedure and its assumptions.

No confidence interval for the primary comparison is reported in the registry record. As a result, the precision of a comparative CAPS-5 effect cannot be assessed from the posted outcome summaries alone. The registry’s note that a two-arm comparison is missing or not estimable is important: the arm-level means and standard deviations should not be treated as a substitute for an inferential result.

Why can over-dispersion matter?

In general, over-dispersion means that observed variability is greater than a statistical model expects. It can make standard errors too small if the model fails to account for that extra variation, producing confidence intervals that are too narrow and tests that appear more certain than warranted. Appropriate handling depends on the outcome type and model. The CAPS-5 endpoint is continuous, and the registry does not report a fitted model or an over-dispersion assessment. Therefore, over-dispersion should not be presented as a diagnosed feature of this study; it is a general issue relevant when a model’s variability assumptions are inadequate.

What can be inferred from a randomized design?

In general, random allocation can support a causal comparison because assignment is intended to create groups that differ by the assigned condition rather than by deliberate selection. That reasoning still depends on appropriate conduct and analysis. Incomplete outcome data, exclusions after randomization, departures from assigned conditions, or selective reporting can affect interpretation. The registry identifies the design as randomized but does not report the allocation procedure, participant flow, adherence, missing outcomes, or analysis population. The design label alone cannot resolve those questions.

The record also identifies double masking, but does not specify who was masked or how masking was maintained. Masking can help reduce certain sources of bias in general, depending on which people are unaware of assignments and how outcomes are assessed. It cannot be assumed from the registry label that every potential source of bias was controlled.

How should planning calculations be read?

In general, sample-size calculations are planning tools that describe the amount of information a future study might need under stated assumptions. The registry’s stated planning approach uses a two-sided significance level of 0.05, equal allocation, and a normal approximation; the target effect is described as a stated fraction of the observed effect. For outcomes other than time-to-event outcomes, the planning quantities refer to participants per arm. These are planning illustrations based on the observed effect, not evidence about the power achieved by this completed trial.

Observed power is not a substitute for an uncertainty interval around the result. A planning calculation based on an observed effect can also be sensitive to how unstable that effect estimate is. No sample-size justification for the original trial, target effect, or protocol-based calculation is reported in the registry record. The record’s planning assumptions should therefore be interpreted as illustrative rather than as proof of the trial’s original design rationale.

Most importantly, the registry lists zero analyses and does not report a formal primary comparison. No particular test, model, covariate adjustment, or missing-data method can be attributed to this trial. General statistical methods can clarify what information a comparative analysis would provide, but they cannot replace a result that is not reported.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Attentional Bias Modification", "Attentional Control Condition")
n   <- c(3, 3)
m   <- c(10.3, 10)
sp  <- c(10.2, 5.3)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Attentional Bias Modification  3  10.300  10.200  -15.038  35.638
CARM  Attentional Control Condition  3  10.000  5.300  -3.166  23.166

11. Multiplicity, Missing Data and Analysis Populations

The registry identifies the CAPS-5 as the primary outcome and lists three secondary measures: PCL-5, PHQ-9, and BAI. It also lists four outcome measures. When several outcomes or multiple comparisons are assessed, the chance of at least one apparently unusual result can increase if each is tested separately. In general, multiplicity procedures can address that issue by adjusting the interpretation or testing strategy. Whether any such procedure was planned or used is not reported in the registry record.

There are no reported results for the secondary measures, and the registry lists zero analyses. It does not identify secondary hypotheses, a hierarchy of outcomes, subgroup analyses, or a multiplicity adjustment. Consequently, the record does not support an assessment of how the trial handled multiple outcome testing, or whether selective emphasis among results was possible.

Missing-data methods are also not reported in the registry record. The record does not describe whether every randomized participant completed the primary assessment, whether outcome data were missing, why data might have been missing, or how missing values were handled. The arm summaries list 3 participants per condition, but that alone does not establish the number randomized, the number assessed, or the analysis population. The enrollment field lists 6 while the brief summary says 20 undergraduate women, and the registry does not reconcile the entries.

The registry record does not state whether analysis followed intention-to-treat principles, included only participants with observed outcomes, or used another population definition. It also does not report protocol deviations or exclusions. These omissions limit assessment of bias and reproducibility; they do not establish that missing data or multiplicity problems occurred.

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

The posted CAPS-5 figures describe the observed arm summaries: a mean of 10.3 with a standard deviation of 10.2 for Attentional Bias Modification, and a mean of 10.0 with a standard deviation of 5.3 for the Attentional Control Condition. Each arm summary lists 3 participants. The registry does not report an estimable comparison between conditions, so these values do not establish whether the groups differed statistically or how precisely any contrast was estimated.

The record does not show that Attention Bias Modification reduced PTSD symptoms, nor does it show that it failed to do so. Those are conclusions about comparative effects, and the required inferential result is not reported in the registry record. The listed means are not evidence of clinical benefit or lack of benefit. No clinically meaningful difference threshold, responder criterion, or outcome interpretation rule is reported.

The record also cannot establish whether the intervention affected PTSD symptom clusters, anxiety, or depression. Although the registry names PCL-5, PHQ-9, and BAI as secondary measures, their results are not reported. Adverse-event fields list zero serious and zero other events in each arm; deaths are not reported in the registry record. These entries should be read as registry fields, not as a complete account of safety monitoring or as proof that no events occurred.

More broadly, the record does not provide enough detail to assess the original enrollment target, participant flow, missing data, adherence, or the analysis population. Its description of 20 undergraduate women does not match the enrollment field of 6, and the discrepancy is not explained. The outcome summaries are therefore limited evidence about the reported groups, not a basis for broad conclusions about all people with PTSD or about survivors of sexual assault generally.

13. Why This Trial Matters Statistically

This trial is statistically notable because it combines a randomized design with a very limited posted primary-outcome record. Randomization is useful for a comparative question, but its value for interpretation depends on knowing how outcomes were analyzed and how participants moved from assignment to assessment. Here, arm-level means and standard deviations are available, while an estimable two-arm comparison is not.

The distinction between descriptive and inferential results matters. Descriptive summaries show the observed group averages and variability. A comparative estimate with an uncertainty interval would show how compatible the data are with a range of possible between-condition effects. Without that estimate, readers should not infer equivalence from similar-looking means or infer a meaningful effect from their difference. The record does not report a primary comparison or its precision.

The enrollment inconsistency is another useful lesson in registry interpretation. The enrollment field lists 6, while the brief summary describes 20 undergraduate women. The record does not clarify how those statements relate to the arm-level outcome summaries, each of which lists 3 participants. Transparent participant flow and clearly defined analysis populations are essential for understanding what a result represents.

The registry also illustrates why outcome completeness and statistical plans matter. It names three secondary measures but reports no results for them, lists zero analyses, and does not describe multiplicity or missing-data handling. These gaps do not establish that the study was conducted improperly, but they constrain independent assessment and make it difficult to distinguish an unreported analysis from an unavailable one.

For biostatistical interpretation, the key is to separate the reported measurements from the claims that would require a comparative analysis. The posted data support a description of the CAPS-5 arm summaries and the registry’s stated design. They do not provide the precision or analysis detail needed to resolve the primary between-condition question.

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 trial-specific limitation in the registry record is the mismatch between the enrollment field, which lists 6, and the brief summary, which describes 20 undergraduate women. The record does not indicate whether the summary reflects an intended population, a different enrollment figure, or another stage of the study. The arm summaries each list 3 participants, but the registry does not provide a participant-flow account linking enrollment, randomization, assessment, and analysis.

The primary endpoint is summarized by arm, but the record explicitly indicates that values are missing or not estimable for a two-arm comparison of the continuous outcome. It does not report an effect estimate, confidence interval, or p-value for the primary contrast. The registry lists zero analyses, and the statistical methods used for any analysis are not reported.

Intervention and control descriptions are incomplete. Both refer to four 20-minute sessions across two weeks, but the available task descriptions end partway through the explanation of the word-pair presentations. The registry does not report adherence, treatment fidelity, or the masking procedures. The reference point for the CAPS-5 timeframe of within three days is also not specified.

Secondary outcomes are named but their results are not reported. The registry does not report missing-data handling, the analysis population, multiplicity procedures, or a sample-size justification for the original design. The stated planning assumptions are illustrations based on the observed effect and should not be mistaken for evidence of the trial’s original planning or observed power. Finally, the registry summary concerns undergraduate women at a Midwest university; the record does not support generalization beyond the described study context.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Using Attentional Bias Modification to Address Trauma Symptoms — NCT02615717.
• Registry record last updated 2017-02-03; status last verified 2016-12.
• Results first posted 2017-02-03.
• 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 registry record identifies NCT02615717 as a completed, randomized, double-masked, parallel study sponsored by University of Nebraska Lincoln. It concerns posttraumatic stress disorder and compares Attentional Bias Modification with an Attentional Control Condition. The study start is listed as 2015-11, with primary completion in 2016-04; phase is listed as NA.

The primary outcome is the CAPS-5 total score, reported as a mean and standard deviation, with a timeframe of within three days. The arm summaries list means of 10.3 and 10.0, standard deviations of 10.2 and 5.3, and 3 participants in each arm. The registry indicates that a two-arm comparison is missing or not estimable and lists zero analyses. It names PCL-5, PHQ-9, and BAI as secondary measures, but their results are not reported.

The brief summary describes 20 undergraduate women, while the enrollment field lists 6. This difference is not explained in the registry record. Details about the analysis population, missing data, multiplicity, and the formal statistical analysis are not reported.