Exposure-Based Treatment for Undifferentiated Somatic Symptom Disorder: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Exposure-Based Treatment for Undifferentiated Somatic Symptom Disorder (NCT04511286), a na na study. The primary outcome is Feasibility 1: Distribution of Physical Symptoms.

2. Clinical Question

The clinical question is therefore not a controlled test of whether exposure-based treatment outperforms another treatment or usual care. Instead, the study concerns the feasibility of delivering a general internet-based exposure protocol to adults with somatic symptom disorder, alongside measurement of symptoms and other patient-reported outcomes. The listed primary measure is taken at the pre-treatment assessment, within 2 weeks before treatment. A pre-treatment score can describe participants’ symptoms at that point, but by itself it does not measure change during treatment.

Because there is no comparison group, any within-group change, if reported, would need to be interpreted as change observed among participants rather than as an estimate of the treatment’s effect relative to an alternative. The registry record does not report outcome analyses, so it does not establish how participants scored on the listed measures or how feasible the treatment was in practice.

3. Trial Design

NCT04511286 is titled Exposure-Based Treatment for Undifferentiated Somatic Symptom Disorder. The official title describes it as a single-arm feasibility study. Karolinska Institutet is listed as the sponsor, and the study is based at the institute in Stockholm, Sweden. The registry lists the study as completed. Its recorded start date is 2020-09-11, and its primary completion date is 2021-02-24.

The design is prospective and single-group. The intervention is an eight-week course of therapist-guided exposure-based treatment delivered via the Internet. The description says exposure is based on general principles and tailored to suit each patient’s needs. The registry lists no allocation scheme and no masking; the study model is single group. Its phase is recorded as NA, which is not a phase designation.

The enrollment field lists 33, while the brief study summary says 40 adults are enrolled. These two figures do not agree, and the registry record does not explain the difference. They should not be treated as interchangeable or reconciled by assumption.

A single-group feasibility design can describe delivery and participant experience, and can characterize measured outcomes within the group. It cannot provide a randomized comparison with a control arm. The registry notes that within-group effects were intended to be quantified and discussed in relation to existing literature, but the analysis count is listed as 0 and no outcome analysis is reported in the record. The planned comparisons and analysis procedures beyond that description 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: All participants were enrolled in treatment.

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 Feasibility 1: Distribution of Physical Symptoms, measured over Pre-treatment assessment (within 2 weeks before treatment).

The listed primary endpoint is the distribution of physical symptoms at the pre-treatment assessment, which is specified to occur within 2 weeks before treatment. It uses the Patient Health Questionnaire-15 (PHQ-15). The registry describes the measure as a score on a scale, with a theoretical range of 0-30; higher scores indicate more distressing physical symptoms. The summary measure is the mean, and the stated dispersion is the full range.

A mean describes the average score in the assessed group. The full range describes the lowest and highest observed scores, giving a sense of how widely individual scores vary. These are descriptive summaries: they can characterize the group’s pre-treatment symptom scores, but they do not by themselves indicate treatment-related change or establish a treatment effect.

The PHQ-15 is relevant to a study of somatic symptom disorder because it measures physical symptoms and their associated distress, as described in the registry. A pre-treatment assessment can document the symptom distribution before the intervention begins. It may also provide context for interpreting later measurements if those are reported, but the registry record does not give a later PHQ-15 result or a comparison between pre-treatment and post-treatment scores.

No mean or observed full range for this endpoint is reported in the registry record. Consequently, the endpoint’s definition and timing are available, but its observed distribution cannot be described from the record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The central statistical feature of this study is its single-group design. All participants are described as receiving the same internet-delivered exposure-based intervention, and the registry does not list a concurrent control arm. This determines what the analysis can establish. Descriptive summaries can report the distribution of measured characteristics or outcomes in the group. If measurements are taken at more than one time, a within-group analysis can describe change over time. Neither approach, by itself, separates intervention effects from other possible explanations for observed change.

What does a mean describe?

A mean is the arithmetic average of the scores included in a summary. It offers a compact description of the group’s typical score, but it can conceal variation between participants. The primary endpoint specifies both the mean and full range. The range communicates the span from the lowest observed score to the highest observed score; it does not show how scores are distributed between those endpoints. The registry provides the theoretical PHQ-15 range, but not the observed mean or observed range.

Why does the endpoint timing matter?

The primary PHQ-15 assessment is specified as occurring before treatment, within 2 weeks before treatment. That timing makes it a baseline description, not a treatment-response result. A baseline score may help characterize the group at entry, but a claim about change would require an outcome measured at another time and a defined analysis comparing measurements. The registry record does not report a primary endpoint analysis or a result at another time for this measure.

What can a single-group analysis tell us?

In a single-group study, observed change can be described within the participants who contribute measurements. General statistical interpretation distinguishes this from a controlled treatment effect. Changes can coincide with treatment while also reflecting other factors, such as the natural course of symptoms, changes in reporting, or other experiences during the study. A concurrent comparison group helps address some of these alternative explanations, but this study is not recorded as having one. No causal treatment estimate should therefore be inferred from the design description alone.

The study summary says within-group effects would be quantified and discussed in relation to existing literature. The registry does not report the effect estimates or the analysis details. The listed analysis count is 0. The exact model, handling of repeated measurements, covariate adjustment, and method for quantifying within-group effects are not reported in the registry record.

What does a confidence interval mean?

In general, a confidence interval expresses the uncertainty around an estimated quantity under a specified statistical method. A narrower interval indicates greater precision under that method, while a wider interval indicates less precision. An interval does not correct for limitations in study design, measurement, or missing information. No confidence interval for a clinical outcome is reported in the registry record, so the precision of an outcome estimate cannot be evaluated.

Why do over-dispersion and distributional assumptions matter?

In general, over-dispersion occurs when the variation in data is greater than a statistical model expects. If a model assumes less variability than the data contain, its uncertainty estimates can be too small. Model choice should reflect the outcome type and its observed distribution. The registry record does not report a model for the primary endpoint or enough outcome data to assess distributional features such as over-dispersion. This is a general consideration, not a claim about the PHQ-15 data in this study.

How should planning illustrations be read?

The registry describes planning illustrations based on an observed effect, a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It also says the effect to detect is expressed as a stated fraction of the observed effect, and distinguishes participant-per-arm planning from total-event planning for time-to-event outcomes. These are hypothetical planning assumptions, not features of the single-group study design. The registry record does not report calculated planning results or an observed effect estimate in the information available for this analysis. Any sample-size illustration should be understood as a planning exercise, not as observed power or evidence that the study detected an effect.

In general, planned sample size concerns the design of a future or hypothetical analysis, whereas observed power is not a substitute for reporting an effect estimate and its uncertainty. The study’s own sample-size justification is not reported in the registry record. No assumption about its intended statistical plan or the rationale for its enrollment figure can be made from the design description.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists 21 outcome measures and 0 analyses. Multiple outcomes raise a general multiplicity issue: when many statistical tests are performed, the chance of at least one apparently unusual result can increase if each test is interpreted independently. Researchers may address this through a prespecified hierarchy, adjustment procedure, or a clear distinction between confirmatory and exploratory outcomes. The registry record does not report a multiplicity procedure, an outcome hierarchy, or which outcomes were treated as confirmatory.

The secondary outcomes listed include PHQ-15, SSD-12, the preliminary Symptom Preoccupation Scale, HAI-14, ASI, GAD-7, PHQ-9, and WHODAS 2.0. The record also describes feasibility outcomes such as credibility and expectancy, adherence, satisfaction, and negative events. It does not report results or analysis details for these measures. The listed count of outcome measures should not be read as a count of completed statistical tests, particularly because the analysis count is recorded as 0.

Missing-data methods and the number of participants contributing to each clinical outcome are not reported in the registry record. It is not stated whether analyses used all available measurements, a defined analysis population, imputation, or another approach. The analysis populations are not reported in the registry record. The enrollment field lists 33, while the summary describes 40 adults; the record does not explain the difference, and it does not identify the population used for each outcome analysis.

In general, missing-data assumptions matter because conclusions can depend on why measurements are absent and how the analysis handles them. Without reported numbers of missing measurements, reasons for missingness, and analytic methods, the completeness and potential selection effects of outcome results cannot be assessed.

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.

Most frequent non-serious adverse event terms

The registry lists 0 serious adverse events among 33 at risk for serious events. It lists 5 other adverse events among 32 at risk for other events, and 0 deaths. These are the recorded counts and denominators; the registry record does not provide event descriptions in the serious-event terms list.

The at-risk denominators differ between the serious-event and other-event entries. The record does not explain why, so no reason should be inferred. The counts should also be read in their respective categories: the record does not state that the serious-event and other-event denominators refer to identical sets of participants.

These figures are descriptive safety information, not a comparison between treatments. With no concurrent control group, they cannot establish whether an event rate was higher or lower than it would have been under another treatment or no intervention. The counts do not identify when events occurred, their severity beyond the serious-event classification, or whether they were judged related to the intervention. Such details are not reported in the registry record.

A count of 0 recorded serious adverse events does not demonstrate that serious harms are impossible, and the other-event count should not be interpreted as a measure of treatment effectiveness. The figures describe what the registry reports for this study, subject to the limitations of the listed denominators and missing event detail.

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

The registry record establishes that this was a prospective, single-group feasibility study of therapist-guided internet-delivered exposure-based treatment for adults with somatic symptom disorder. It specifies an eight-week intervention and lists a pre-treatment PHQ-15 measure of physical symptoms as the primary endpoint. It also identifies patient-reported and feasibility-related outcomes and provides limited safety counts.

It does not report the primary endpoint’s observed mean or range, analyses of secondary outcomes, or estimates of change. As a result, the record does not show what symptom scores participants had, how scores varied, or whether scores changed during treatment. It also does not report the study’s findings on credibility, expectancy, adherence, satisfaction, or the negative events described in the summary.

The single-group design is suitable for describing the study’s intervention and, with reported data, could support descriptive assessments of feasibility and within-group outcomes. It cannot provide a randomized estimate comparing treatment with a control condition. Even a reported change over time would not by itself show that the intervention caused the change. In this record, no such outcome analysis is reported.

The safety entries report no serious adverse events and no deaths, alongside other adverse events. They are not comparative safety estimates, and event details are not available in the registry record. The enrollment field and brief summary also give different participant counts, with no explanation of the difference.

Accordingly, the available record supports conclusions about the study’s design and the outcomes it intended to measure, not about clinical benefit, lack of benefit, or the overall feasibility result. The absence of reported analyses is an information gap; it is not evidence that outcomes were absent or that the intervention did or did not produce change.

13. Why This Trial Matters Statistically

This study is statistically interesting because it focuses on feasibility in a clinical area where the intervention is described as a general exposure protocol tailored to individual needs. Feasibility studies often need to describe more than symptom scores: participant experience, adherence, acceptability, and negative events can all inform whether a protocol can be delivered and evaluated. The registry summary names several of these domains, while the listed primary endpoint is a pre-treatment symptom distribution.

The distinction between feasibility questions and efficacy questions is important. Descriptive information can help characterize the participants and the conduct of a study. A single-group design can also support within-group descriptions if results are reported. But without a comparator, it cannot directly estimate how outcomes would differ under another condition. Statistical interpretation should therefore match the design rather than treating a within-group result as a controlled effect.

The registry’s absence of outcome analyses is also consequential. The record contains endpoint definitions and safety counts, but not the clinical estimates needed to assess the observed symptom distribution, change, or precision. Registering measures is not the same as reporting their results. A transparent account of estimates, uncertainty, missing data, and analysis populations would be needed to evaluate the outcomes statistically.

Finally, the differing participant counts in the enrollment field and the study summary illustrate why clear reporting of planned, enrolled, and analyzed populations matters. The registry does not explain the difference. That uncertainty limits a reader’s ability to connect design descriptions with the populations represented by outcome and safety data. These points matter for interpreting this feasibility study without asking it to answer a comparative question its design does not address.

14. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

Several limitations specific to this study affect interpretation of the registry record. First, the design is single group, with no like-for-like control comparison. This limits the conclusions that could be drawn about treatment effects, even if within-group outcome changes were available. The study is described as a feasibility investigation, and the registered design should not be read as a randomized efficacy comparison.

Second, the primary endpoint is specified at a pre-treatment assessment within 2 weeks before treatment. The record does not report the observed PHQ-15 mean or full range, nor does it provide a primary endpoint analysis. The endpoint definition therefore does not show the participants’ actual symptom distribution or change after treatment.

Third, the enrollment field lists 33, whereas the brief summary describes 40 adults. The registry record does not explain this difference. It also does not identify outcome-specific analysis populations or explain whether the safety denominators reflect the same participants. This makes the relationship between the described study population and the reported counts unclear.

Fourth, the registry lists 21 outcome measures and 0 analyses. It does not report outcome estimates, uncertainty intervals, missing-data handling, analysis methods, or multiplicity procedures. Without these details, the completeness and precision of any clinical findings cannot be assessed from this record.

Finally, the intervention is tailored to individual needs, as described in the summary. The registry record does not report how tailoring was implemented or measured, so the degree of variation in treatment delivery cannot be characterized. The feasibility thresholds or criteria used to judge success are also not reported in the registry record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Exposure-Based Treatment for Undifferentiated Somatic Symptom Disorder — NCT04511286.
• Registry record last updated 2025-03-19; status last verified 2025-03.
• Results first posted 2025-03-19.
• 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

NCT04511286 is a completed, prospective single-group feasibility study sponsored by Karolinska Institutet. It evaluates eight weeks of therapist-guided exposure-based treatment delivered via the Internet for adults with somatic symptom disorder. The registry lists the primary measure as the pre-treatment distribution of physical symptoms on the PHQ-15, with a theoretical range of 0-30 and higher scores indicating more distressing physical symptoms.

The enrollment field lists 33, while the brief summary describes 40 adults; the record does not explain the difference. It lists 21 outcome measures and 0 analyses. The primary endpoint result and analyses of the other clinical and feasibility outcomes are not reported in the registry record. Safety entries list 0 serious adverse events, 5 other adverse events, and 0 deaths, with different at-risk denominators for serious and other events.

The single-group design supports description, not a randomized treatment comparison. The record does not provide enough outcome analysis to assess symptom change or the study’s overall feasibility findings.