The research team assembled a mixed sample of 955 participants drawn from Iran, combining 143 psychiatric patients who met DSM-5 criteria for somatic symptom and related disorders (SSRD) with 812 individuals from the general population who did not carry that diagnosis. The sample had an average age of 34.2 years, with a standard deviation of 11.5 years, and was 66 percent female. This design deliberately blended a clinically severe group with community participants, allowing the investigators to examine how somatization relates to other forms of psychopathology across a wide spectrum of severity rather than only within a narrow patient population.

Methodologically, the study took what the authors describe as a multidimensional approach. Participants completed a battery of self-report questionnaires covering somatic symptoms, psychological syndromes such as depression and anxiety, and two distinct ways of characterizing personality pathology. The first, criterion-based approach reflects the traditional categorical diagnosis of personality disorder, in which individuals are judged against diagnostic checklists. The second, trait-based approach follows the newer dimensional model, assessing maladaptive personality traits as continuous dimensions. By including both frameworks, the researchers could test whether the answer to their question depended on how personality pathology is defined — a critical check, because the field of personality assessment is currently in transition between these two paradigms.

To reduce the many questionnaire items to interpretable constructs, the team used exploratory factor analysis, a statistical technique that identifies clusters of variables that covary together and can be treated as underlying latent dimensions. This procedure extracted four factors corresponding to somatization, psychological syndromes, criterion-based personality disorder, and maladaptive trait-based personality pathology. In other words, the data themselves organized into the conceptual categories the researchers set out to compare, providing a clean foundation for the predictive analyses that followed.

The heart of the study lay in hierarchical linear regression, a technique that allows researchers to enter predictors in stages and measure how much additional variance each block explains. Here the logic was straightforward but powerful: if somatization were fundamentally a manifestation of personality pathology, then personality measures should explain substantial variance in somatic symptom reporting even after current psychological distress is statistically controlled. Conversely, if somatization is chiefly tied to present distress, the psychological syndromes factor should dominate. The results were unambiguous, and the effect sizes were striking.

Compared with criterion-based personality disorder, the psychological syndromes factor was far more strongly related to the somatization factor. The psychological syndromes accounted for an R-squared of 0.512, meaning they explained just over half of the variance in somatization scores, whereas criterion-based personality pathology explained only 0.105. In the hierarchical models, the incremental contribution — the change in R-squared — was 0.414 for psychological syndromes against a mere 0.007 for criterion-based personality disorder. The same pattern emerged when the trait-based model was used instead: psychological syndromes achieved an R-squared of 0.512 versus 0.138 for maladaptive traits, with incremental values of 0.377 versus 0.004. Whichever lens was applied to personality, the conclusion held.

The team also examined a single-item, pain-related measure as a separate outcome, and here too psychological syndromes outperformed both personality frameworks, though with smaller absolute effects. The syndromes factor explained an R-squared of 0.151 for the pain measure, compared with 0.067 for criterion-based personality disorder and 0.066 for trait-based pathology. The incremental contributions were 0.086 for psychological syndromes against 0.003 and 0.001 for the two personality approaches respectively. The authors are careful to note that these pain findings rest on a single-item indicator and should not be generalized to multidimensional assessments or to chronic pain conditions, where the underlying dynamics may differ considerably.

What do these numbers mean conceptually? The authors conclude that somatization appears to be a phenomenon primarily related to psychological distress rather than to personality pathology, and that this holds regardless of the theoretical context used to define personality problems. This does not mean personality pathology is irrelevant. The study found that both criterion-based and trait-based personality pathology were independently related to somatization, so the association is real. But when current psychological distress is taken into account, personality pathology shrinks to a marginal predictor. In practical terms, a patient’s present levels of depression, anxiety, and related syndromes carry most of the predictive signal for bodily symptom reporting, while personality structure adds only a thin residual layer of explanation.

The clinical implications are significant. Somatization is notoriously difficult to treat, and patients with somatic symptom and related disorders often consume substantial health care resources through repeated investigations and specialist referrals that yield little relief. If the strongest statistical lever for understanding somatization is current psychological distress rather than entrenched personality pathology, then interventions targeting distress — such as treatments for depression and anxiety — may offer the most direct route to reducing the burden of somatic symptoms. The authors explicitly frame their findings as a way to refine theoretical models and improve clinical outcomes by targeting the most impactful constructs, and the variance figures suggest that distress-focused constructs are precisely those impactful targets.

The study also carries methodological lessons for the research community. Because the pattern of results was consistent across both categorical and dimensional conceptualizations of personality pathology, the conclusion is not an artifact of one diagnostic school. The use of factor analysis to establish latent dimensions before regression, and the hierarchical entry of predictors to isolate incremental validity, provide a template for similar comparative questions in psychopathology research. The work was approved by the ethics committee of the Mind GPS Institute of Kermanshah, Iran, conducted in accordance with the Helsinki Declaration, and supported methodologically by that institute without external funding. As with any cross-sectional, self-report study, causal direction cannot be established, and the general-population sample from a single country invites replication elsewhere. Yet the sheer size of the gap — psychological syndromes explaining roughly half the variance in somatization while personality pathology explains a tenth or less — makes this one of the clearer statistical verdicts the field has received on a long-standing debate, and it points clinicians firmly toward treating the distress, not just the personality, when the body speaks for the mind.

Subject of Research: The relative contribution of psychological syndromes and personality pathology to somatization

Article Title: Relative sensitivity of phenotypic personality pathology and psychological syndromes to somatization phenomenon: a multidimensional approach

Article References: Komasi, S., Macina, C., Miettunen, J., Nazari, A., Heydarpour, B., Shams-Alizadeh, N., & Amianto, F. (2026). Relative sensitivity of phenotypic personality pathology and psychological syndromes to somatization phenomenon: a multidimensional approach. Discover Mental Health. https://doi.org/10.1007/s44192-026-00615-0

Image Credits: AI Generated

DOI: 10.1007/s44192-026-00615-0

Keywords: somatization, somatic symptom and related disorders, personality pathology, psychological distress, DSM-5, hierarchical regression, factor analysis, maladaptive traits, pain, psychopathology, mental health, Relative

The study, published in the journal Current Psychology by Anna Włodarska, Anna Zajenkowska, and Izabela Kaźmierczak of VIZJA University in Warsaw, addresses a long-standing methodological worry known as volunteer bias or self-selection bias. Scientific research is vulnerable to both random error, which scatters measurements unpredictably, and systematic error, which pushes them consistently in one direction. Random error can be tamed with larger samples and better instruments. Systematic error is more insidious, because it can masquerade as a genuine finding. If the people who volunteer for studies differ from the population they are meant to represent, then every downstream statistic inherits that distortion, no matter how elegant the analysis.

Volunteer bias has been documented for decades in psychology, where researchers have repeatedly noticed that participants in behavioral studies tend to score differently on personality and affect measures than non-volunteers. Earlier work by some of the same Polish team, published in PLOS ONE in 2023, found that personality and affective disturbances were prevalent among participants in psychological studies, hinting that the problem extended beyond simple demographic skew. The new study extends that logic into clinical research, where the stakes are considerably higher. Clinical trials generate the evidence on which drug approvals, treatment guidelines, and ultimately patient care depend. If trial volunteers carry a distinctive psychological profile, the safety and efficacy data produced by those trials may not generalize cleanly to the broader patient population.

To investigate, the team drew on a representative community sample of Polish adults, a design choice that matters enormously. Most studies of volunteer bias compare actual trial participants with actual non-participants at a single research site, which limits what can be said about the wider population. By surveying a representative cross-section of the community and simply asking respondents about their interest in participating in psychological studies and clinical trials, the researchers could estimate how personality pathology is distributed across the willing and the unwilling in the population at large. Participants completed validated measures, including the Polish adaptations of the Personality Inventory for ICD-11 and the Level of Personality Functioning Scale-Brief Form 2.0, alongside the Patient Health Questionnaire-9 for depressive symptoms.

The theoretical framework underlying the measurement is worth understanding, because it represents a major shift in how psychiatry conceptualizes personality disorder. Both the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders and the eleventh edition of the International Classification of Diseases have moved toward dimensional models, in which personality pathology is understood as a matter of degree rather than a set of discrete categories. The ICD-11 model assesses two things: a level of personality functioning, which captures how severely a person’s sense of self and relationships are impaired, and a set of pathological trait domains, including negative affectivity, disinhibition, dissociality, and others. This dimensional approach allowed the Polish team to measure personality pathology continuously across their entire sample rather than only in people with formal diagnoses.

The results were striking in their consistency. Individuals who said they were interested in participating in clinical trials showed lower levels of personality functioning, meaning greater impairment in self-organization and interpersonal capacities, than those who were not interested. They also scored higher on negative affectivity, the trait domain encompassing anxiety, emotional lability, and a tendency to experience distressing emotions, and on disinhibition, which reflects impulsivity and difficulty with planning and restraint. Dissociality, a trait involving callousness and disregard for the rights and feelings of others, was likewise elevated. On top of the personality findings, interested respondents reported more depressive symptoms than their uninterested peers, suggesting that mood disturbance and personality pathology travel together in the population of potential volunteers.

Perhaps the most intriguing finding concerned the type of trial. The highest scores on personality pathology and depressive symptoms appeared among respondents interested specifically in psychiatric drug trials. The authors suggest a plausible explanation rooted in perceived benefit: people struggling with psychological distress may see psychiatric drug trials as a route to new treatments and structured care that they might not otherwise access. This creates a paradox with real methodological consequences. The very trials designed to evaluate psychiatric medications may disproportionately attract participants whose personality functioning is impaired, meaning the samples on which psychiatric drug evidence rests could be psychologically distinctive in ways that current screening rarely captures.

Why should this matter for the integrity of trial results? Prior research offers several concrete mechanisms. Psychopathological traits have been shown to influence participant behavior in ways that complicate protocol adherence and data accuracy. Neuroticism, a close cousin of negative affectivity, is associated with larger and more prolonged physiological responses to emotional stimuli, altered cortisol reactivity, and even differences in antibody response to vaccination, all of which could interact with the outcomes a trial is designed to measure. Depressive symptoms can bias decision-making, and personality pathology is linked to poorer treatment outcomes and higher treatment utilization in clinical populations. Participants with elevated disinhibition may struggle with the demands of strict dosing schedules and follow-up visits, while those with high negative affectivity may report side effects differently, skewing safety data in either direction.

The study’s authors argue that their findings highlight the importance of screening trial participants for personality pathology, not to exclude them from research, but to account for their characteristics in the design and analysis of studies. There is a delicate ethical balance here. Volunteers with psychological distress are precisely the people who may benefit most from access to experimental treatments, and excluding them wholesale would be both unfair and scientifically wasteful. But ignoring the pattern risks a subtler form of harm: trial results that look generalizable but are actually calibrated to a psychologically atypical subset of the population, with safety profiles and efficacy estimates that may not transfer to typical patients.

The research, which was part of a larger project on hostile attribution and was approved by the Maria Grzegorzewska University Research Ethics Committee, adds a compelling new dimension to an old methodological conversation. It suggests that the gate through which every participant passes, the decision to volunteer, is itself psychologically patterned, and that the pattern runs toward pathology rather than away from it. For a field that has invested enormously in randomization, blinding, and statistical rigor, the message is humbling: some of the most consequential selection into the evidence base happens before a single protocol procedure begins. As clinical science grapples with replication problems and questions about generalizability, understanding who volunteers, and why, may prove to be one of the most underappreciated levers for improving the reliability of medicine itself.

Subject of Research: Volunteer bias in clinical trials linked to personality pathology and depressive symptoms

Article Title: Personality pathology and willingness to participate in psychological and clinical trials

Article References: Włodarska, A., Zajenkowska, A., & Kaźmierczak, I. (2026). Personality pathology and willingness to participate in psychological and clinical trials. Current Psychology, 45(19), Article 1566. https://doi.org/10.1007/s12144-026-10067-y

Image Credits: AI Generated

DOI: 10.1007/s12144-026-10067-y

Keywords: volunteer bias, selection bias, personality pathology, clinical trials, depressive symptoms, ICD-11, negative affectivity, disinhibition, psychiatric drug trials, research methodology, personality functioning, self-selection