The latent structure of the functional dyspepsia symptom complex: a taxometric analysis

Dimensions over categories: a meta-analysis of taxometric research

Taxometric procedures have been used extensively to investigate whether individual differences in personality and psychopathology are latently dimensional or categorical ('taxonic'). We report the first meta-analysis of taxometric research, examining 317 findings drawn from 183 articles that employed an index of the comparative fit of observed data to dimensional and taxonic data simulations. Findings supporting dimensional models outnumbered those supporting taxonic models five to one. There were systematic differences among 17 construct domains in support for the two models, but psychopathology was no more likely to generate taxonic findings than normal variation (i.e. individual differences in personality, response styles, gender, and sexuality). No content domain showed aggregate support for the taxonic model. Six variables - alcohol use disorder, intermittent explosive disorder, problem gambling, autism, suicide risk, and pedophilia - emerged as the most plausible taxon candidates based on a preponderance of independently replicated findings. We also compared the 317 meta-analyzed findings to 185 additional taxometric findings from 96 articles that did not employ the comparative fit index. Studies that used the index were 4.88 times more likely to generate dimensional findings than those that did not after controlling for construct domain, implying that many taxonic findings obtained before the popularization of simulation-based techniques are spurious. The meta-analytic findings support the conclusion that the great majority of psychological differences between people are latently continuous, and that psychopathology is no exception.

Latent structure and factor invariance of somatic symptoms in the patient health questionnaire (PHQ-15)

BACKGROUND

Somatic symptoms are highly prevalent in primary care although insufficiently understood. The Patient Health Questionnaire (PHQ-15) is a valuable screening test but it has not yet been possible to unequivocally demonstrate its latent structure and measurement invariance.

METHODS

A total of 1,255 patients from 28 primary care centres suffering symptoms of anxiety, depression or somatisation participated in a clinical trial. They completed the PHQ-15 at baseline and 374 retook it at three months. Exploratory structural equation modelling (ESEM) was used to compare three models: 1) a single global factor for somatisation, 2) four specific correlated factors, and 3) a bifactor model integrating the first two models.

RESULTS

A multi-group invariance analysis of the best-fit model was performed: the bifactor model (χ²=25.17, df=23, p = 0.34, RMSEA=0.009, CFI=1.00, TLI=0.999). Strict invariance was good for both gender (RMSEA = 0.046, CFI = 0.973, TLI = 0.963) and age (RMSEA = 0.048, CFI = 0.964, TLI = 0.962). Configural and metric invariance were confirmed for moment of assessment, but scalar invariance was not.

LIMITATIONS

The two main limitations were the sample (primary care patients with emotional disorders), which was not representative of the general population, and the utilisation of ESEM (vs. confirmatory factor analysis), which did not allow a second-order factor model to be tested.

CONCLUSIONS

PHQ-15 showed a bifactor structure, providing both a single global measure of somatisation and specific measures of pain, gastrointestinal, cardiopulmonary and fatigue factors. Its factor invariance with regard to both gender and age was confirmed.

Functional dyspepsia

Functional dyspepsia is one of the most prevalent functional gastrointestinal disorders. Functional dyspepsia comprises three subtypes with presumed different pathophysiology and aetiology: postprandial distress syndrome (PDS), epigastric pain syndrome (EPS) and a subtype with overlapping PDS and EPS features. Functional dyspepsia symptoms can be caused by disturbed gastric motility (for example, inadequate fundic accommodation or delayed gastric emptying), gastric sensation (for example, sensations associated with hypersensitivity to gas and bloating) or gastric and duodenal inflammation. A genetic predisposition is probable but less evident than in other functional gastrointestinal disorders, such as irritable bowel syndrome (IBS). Psychiatric comorbidity and psychopathological state and trait characteristics could also play a part, although they are not specific to functional dyspepsia and are less pronounced than in IBS. Possible differential diagnoses include Helicobacter pylori infection and peptic ulceration. Pharmacological therapy is mostly based on the subtype of functional dyspepsia, such as prokinetic and fundus-relaxing drugs for PDS and acid-suppressive drugs for EPS, whereas centrally active neuromodulators and herbal drugs play a minor part. Psychotherapy is effective only in a small subset of patients, whereas quality of life can be severely affected in nearly all patients. Future therapies might include novel compounds that attempt to treat the underlying gastric and duodenal inflammation.

Examination of competing diagnostic models of functional gastrointestinal disorders related to pain in children

BACKGROUND

There have been no empirical validations of the Rome III or Rome IV criteria in children. The aim of the current study was to examine whether symptoms naturally occur in a pattern consistent with Rome III and/or Rome IV pediatric criteria for functional dyspepsia (FD) and irritable bowel syndrome (IBS).

METHODS

We conducted a retrospective cohort study of 250 children, ages 8-17 years, presenting to an abdominal pain clinic with pain of at least 8 weeks duration. We evaluated patterns of gastrointestinal (GI) and non-gastrointestinal (non-GI) symptoms which had been collected in a standardized fashion as part of routine clinical care. Confirmatory factor analyses were used to compare pre-existing models of symptoms clusters, namely Rome III and Rome IV criteria for IBS and FD in children and adolescents. Factor intercorrelations also were examined to determine whether IBS symptoms and non-GI somatic complaints correlate uniquely with FD symptom clusters.

KEY RESULTS

Both models demonstrated good fit with observed data [3-factor: χ² (101, n=250)110.75, P<.05, TLI=.99, CFI=.99; 4-factor: χ² (98, n=250)117.54, P<.05, TLI=.96, CFI=.97]. Fit indices and intercorrelations favored the more parsimonious 3-factor solution (3-factor: AIC=4654.91, BIC=4778.17; 4-factor: AIC=4757.16, BIC=4890.97) consistent with pediatric Rome III criteria that conceptualizes FD as a single diagnostic category. FD demonstrated significant overlap with IBS (.42), while non-GI-specific symptoms correlated significantly with FD (.64), but not IBS (.14) symptoms.

CONCLUSIONS & INFERENCES

GI symptoms in children presenting for initial evaluation of chronic functional abdominal pain occur in a pattern consistent with Rome III and IV pediatric criteria. Rome III offers a more parsimonious model. The presence of FD symptoms is strongly, and uniquely, associated with non-GI symptoms.