Taxonicity of adolescent melancholia: a categorical or dimensional construct?

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.

Gene-environment interactions between stress and 5-HTTLPR in depression: A meta-analytic update

BACKGROUND

Meta-analyses have yielded contradictory findings concerning the role of 5-HTTLPR in interaction with stress (GxE) in depression. The current meta-analysis investigates if these contradictory findings are a result of differences between studies in methodological approaches towards the assessment of stress and depression.

METHODS

After performing a systematic database search (February to December 2016), first, a meta-analysis was used to investigate the total effect size and publication bias. Second, stratified meta-analyses were used to investigate the potential moderating influence of different methodological approaches on heterogeneity of study findings. Third, a meta-regression was used to investigate the combined influence of the methodological approaches on the overall effect size.

RESULTS

Results showed a small but significant effect of 5-HTTLPR in interaction with stress in the prediction of depression (OR[95%CI] = 1.18[1.09; 1.28], n = 48 effect sizes from 51 studies, totaling 51,449 participants). There was no evidence of publication bias. Heterogeneity of effect sizes was a result of outliers and not due to different methodological approaches towards the assessment of stress and depression. Yet, there was some evidence that studies adopting a categorical and interview approach to the assessment of stress report higher GxE effects, but further replication of this finding is needed.

LIMITATIONS

A large amount of heterogeneity (i.e., 46%) was not explained by the methodological factors included in the study and there was a low response rate of invited studies.

CONCLUSIONS

The current meta-analysis provides new evidence for the robustness of the interaction between stress and 5-HTTLPR in depression.

Taxometric evidence of a dimensional latent structure for depression in an epidemiological sample of children and adolescents

BACKGROUND

A basic phenomenological question of much theoretical and empirical interest is whether the latent structure of depression is dimensional or categorical in nature. Prior taxometric studies of youth depression have yielded mixed findings. In a step towards resolving these contradictory findings, the current taxometric investigation is the first to utilize a recently developed objective index, the comparison curve fit index, to evaluate the latent structure of major depression in an epidemiological sample of children and adolescents.

METHOD

Data were derived from Mental Health of Children and Young People in Great Britain surveys. Participants were administered a structured diagnostic interview to assess for current depression. Parents (n = 683) were interviewed for children aged 5-16 years, and child interviews (n = 605) were conducted for those aged 11-16 years.

RESULTS

MAMBAC (mean above minus below a cut), MAXEIG (maximum eigenvalue) and L-Mode (latent mode) analyses provided convergent support for a dimensional latent structure.

CONCLUSIONS

The current findings suggest that depression in youth is more accurately conceptualized as a continuous syndrome rather than a discrete diagnostic entity.

BDNF Val66Met polymorphism and stressful life events in melancholic childhood-onset depression

INTRODUCTION

Brain-derived neurotrophic factor (BDNF) polymorphisms have been examined for their contribution toward depression with equivocal results. More homogeneous phenotypes might be used to improve our understanding of genetic liability to depression. The aim of our study was to (a) test for an association between the BDNF Val66Met polymorphism and childhood-onset melancholic depression and (b) to examine the interactive effects of stressful life events (SLE) and the Val66Met polymorphism on the risk of childhood-onset melancholic depression.

MATERIALS AND METHODS

A total of 583 depressed probands were involved in this study (162 of the melancholic subtype). Diagnoses were derived through the Interview Schedule for Children and Adolescents - Diagnostic Version and life event data were collected using an Intake General Information Sheet.

RESULTS

Overall, 27.8% of the participants fulfilled the criteria for melancholy. In the melancholic group, the proportion of females was higher (53.1%), although there were more males in the overall depressed sample. We detected no significant differences in genotype or allele frequency between the melancholic and the nonmelancholic depressed group. The BDNF Val66Met polymorphism and SLE interaction was not significantly associated with the melancholy outcome.

CONCLUSION

In our study, females were more prone to developing the early-onset melancholic phenotype. To our knowledge, this is the first study to investigate the differentiating effect of the genotype and the G×E interaction on the melancholic phenotype in a large sample of depressed young patients. We did not find an association between the melancholic subtype of major depression and the BDNF genotype and SLE interaction in this sample, which is representative of the Hungarian clinic-referred population of depressed youths.

Validity and clinical utility of the current operational characterization of major depression

The operational definition of major depression has remained more or less the same in the past 40 years. An appraisal of currently available research data leads to the conclusion that further evidence is needed about (1) where to fix the boundary between cases and non-cases in order to improve the clinical utility of the diagnosis, (2) the validity and clinical utility of the construct of melancholia as a qualitatively distinct subtype of depression, and (3) the validity and clinical utility of a 'contextual' exclusion criterion. Furthermore, we need a more precise description of individual depressive symptoms, an exploration of the predictive value of these symptoms and of clusters of them, especially concerning clinical outcome and treatment response, and a clearer operationalization of the impairment criterion.

Categories versus dimensions in personality and psychopathology: a quantitative review of taxometric research

Taxometric research methods were developed by Paul Meehl and colleagues to distinguish between categorical and dimensional models of latent variables. We have conducted a comprehensive review of published taxometric research that included 177 articles, 311 distinct findings and a combined sample of 533 377 participants. Multilevel logistic regression analyses have examined the methodological and substantive variables associated with taxonic (categorical) findings. Although 38.9% of findings were taxonic, these findings were much less frequent in more recent and methodologically stronger studies, and in those reporting comparative fit indices based on simulated comparison data. When these and other possible confounds were statistically controlled, the true prevalence of taxonic findings was estimated at 14%. The domains of normal personality, mood disorders, anxiety disorders, eating disorders, externalizing disorders, and personality disorders (PDs) other than schizotypal yielded little persuasive evidence of taxa. Promising but still not definitive evidence of psychological taxa was confined to the domains of schizotypy, substance use disorders and autism. This review indicates that most latent variables of interest to psychiatrists and personality and clinical psychologists are dimensional, and that many influential taxonic findings of early taxometric research are likely to be spurious.

Annual research review: categories versus dimensions in the classification and conceptualisation of child and adolescent mental disorders--implications of recent empirical study

The question of whether child and adolescent mental disorders are best classified using dimensional or categorical approaches is a contentious one that has equally profound implications for clinical practice and scientific enquiry. Here, we explore this issue in the context of the forth coming publication of the DSM-5 and ICD-11 approaches to classification and diagnosis and in the light of recent empirical studies. First, we provide an overview of current category-based systems and dimensional alternatives. Second, we distinguish the various strands of meaning and levels of analysis implied when we talk about categories and dimensions of mental disorder--distinguishing practical clinical necessity, formal diagnostic systems, meta-theoretical beliefs and empirical reality. Third, we introduce the different statistical techniques developed to identify disorder dimensions and categories in childhood populations and to test between categorical and dimensional models. Fourth, we summarise the empirical evidence from recent taxometric studies in favour of the 'taxonomic hypothesis' that mental disorder categories reflect discrete entities with putative specific causes. Finally, we explore the implications of these findings for clinical practice and science.

Development and validation of the current concept of major depression

The operational diagnostic criteria for major depression have remained more or less the same in the past 40 years. However, the threshold for the diagnosis fixed by operational definitions has been criticized for either being too high, excluding many depressive states which do not differ from currently defined major depression on several variables, or too low, so that the milder cases receiving the diagnosis do not respond to antidepressants better than to placebo. Furthermore, it has been stated that current operational criteria do not convey anymore the gestalt of the depressive syndrome, and that they lead to the inclusion under the heading of depression of several homeostatic responses to adverse life events. This paper reviews the development and validation of the current concept of major depression and identifies priorities for future research.

Latent structure of unipolar and bipolar mood symptoms

OBJECTIVES

  The taxonic versus dimensional status of mood symptoms has been the subject of debate among mental health professionals. Conventional diagnostic models suggest that mood disorders are categorical; however, the inability of categorical models to adequately account for subthreshold unipolar and bipolar presentations and the heterotypic continuity of symptoms in unipolar and bipolar cases has resulted in growing support for dimensional views. The current study sought to evaluate the relative viabilities of categorical and dimensional models of mood symptoms within a taxometric framework.

METHODS

  We examined the latent structure of mood symptoms in an epidemiological sample drawn from the Collaborative Psychiatric Epidemiological Surveys. Using three taxometric procedures (MAMBAC, MAXEIG, and L-Mode), we analyzed indicators of mania and depression created from the mood symptoms section of the survey.

RESULTS

  The taxometric analyses supported a taxonic rather than dimensional structure for mania and depression. Membership in the mania and depressive taxa was associated with meeting criteria for DSM-IV lifetime manic episode and major depressive disorder, respectively. We identified a subset of 700 individuals falling into both taxa; membership in this subset was associated with lifetime bipolar disorder status. Group membership predicted designated external variables including help-seeking, family history, and duration of impairment. Within taxon and/or complement groups, severity scores still appeared to predict external variables.

CONCLUSION

  Our findings suggest that although taxonic, mood disorders possess meaningful dimensional variation.

The possible role of the kynurenine pathway in adolescent depression with melancholic features

BACKGROUND

Although adolescent major depressive disorder (MDD) is acknowledged to be a heterogeneous disorder, no studies have reported on biological correlates of its clinical subgroups. This study addresses this issue by examining whether adolescent MDD with and without melancholic features (M-MDD and NonM-MDD) have distinct biological features in the kynurenine pathway (KP). The KP is initiated by pro-inflammatory cytokines via induction of the enzyme indoleamine 2,3-dioxygenase (IDO), which degrades tryptophan (TRP) into kynurenine (KYN). KYN is further metabolized into neurotoxins linked to neuronal dysfunction in MDD. Hypotheses were that, compared to healthy controls and to NonM-MDD adolescents, adolescents with M-MDD would exhibit: (i) increased activation of the KP [i.e., increased KYN and KYN/TRP (reflecting IDO activity)]; (ii) greater neurotoxic loads [i.e., increased 3-hydroxyanthranilic acid (3-HAA, neurotoxin) and 3-HAA/KYN (reflecting production of neurotoxins)]; and (iii) decreased TRP. We also examined relationships between severity of MDD and KP metabolites.

METHODS

Subjects were 20 adolescents with M-MDD, 30 adolescents with NonM-MDD, and 22 healthy adolescents. MDD episode duration had to be >or= 6 weeks and Children's Depression Rating Scale-Revised (CDRS-R) scores were >or= 36. Blood samples were collected at AM after an overnight fast and analyzed using high-performance liquid chromatography. Group contrasts relied on analysis of covariance based on ranks, adjusted for age, gender, and CDRS-R scores. Analyses were repeated excluding medicated patients. Fisher's protected least significant difference was used for multiple comparisons.

RESULTS

As hypothesized, KYN/TRP ratios were elevated and TRP concentrations were reduced in adolescents with M-MDD compared to NonM-MDD adolescents (p = .001 and .006, respectively) and to healthy controls (p = .008 and .022, respectively). These findings remained significant when medicated patients were excluded from the analyses. Significant correlations were obtained exclusively in the M-MDD group between KYN and 3-HAA/KYN and CDRS-R.

CONCLUSIONS

Findings support the notion that adolescent M-MDD may represent a biologically distinct clinical syndrome.

Increased waking salivary cortisol and depression risk in preschoolers: the role of maternal history of melancholic depression and early child temperament

BACKGROUND

Elevated morning cortisol is a prospective predictor of major depression and may serve as a vulnerability marker. We examined the relation between morning cortisol and two prominent risk factors for depression in preschool-aged children: maternal depression and child temperament. We also explored whether maternal depression during the child's life, parental hostility and life stress explained these associations.

METHODS

Ninety-four children provided a morning salivary cortisol sample, and 92 children provided an evening sample. Child temperament and parenting were assessed using observational measures, and maternal depression and life stress were assessed with clinical interviews.

RESULTS

Maternal history of melancholic depression and child temperamental low positive emotionality were significantly associated with higher morning cortisol. These relations persisted after controlling for children's negative emotionality and concurrent depressive symptoms, parental hostility, and life stress.

CONCLUSIONS

Our findings support the hypothesis that elevated morning cortisol may serve as an early-emerging vulnerability factor for depression, and highlight the importance of anhedonia in risk for depression.

Latent structure of depression in a Japanese population sample: taxometric procedures

OBJECTIVE

Although the debate on whether mental disorders are categorical or dimensional is critical for researchers and practitioners, past findings of taxometric studies of depression have been somewhat contradictory and difficult to reconcile. One reason for the disagreement was that most researchers relied only on selected samples (students, clinical patients, or screened community samples). The present study investigated whether the latent structure of depression is categorical or dimensional using an unselected general community sample.

METHOD

To determine whether the latent structure of depression assessed by the Center for Epidemiologic Studies Depression Scale is categorical or dimensional, taxometric procedures were carried out on a Japanese general population-based sample of 20 987 individuals selected using a cluster sampling procedure.

RESULTS

Both the means above and below a sliding cut (MAMBAC) and the maximum eigenvalue (MAXEIG) procedures, using indicators drawn from the Center for Epidemiologic Studies Depression scale yielded results that the latent structure of depression is dimensional.

CONCLUSIONS

The dimensional structure of depression should be considered when classifying individual differences and selecting suitable research designs.

A comparison of the predictive abilities of dimensional and categorical models of unipolar depression in the National Comorbidity Survey

BACKGROUND

Taxometric research on depression has yielded mixed results, with some studies supporting dimensional solutions and others supporting taxonic solutions. Although supplementary tests of construct validity might clarify these mixed findings, to date such analyses have not been reported. The present study represents a follow-up to our previous taxometric study of depression designed to evaluate the relative predictive validities of dimensional and categorical models of depression.

METHOD

Two sets of dimensional and categorical models of depression were constructed from the depression items of the Composite International Diagnostic Interview: (1) empirically derived models obtained using latent structure analyses and (2) rationally selected models, including an additive depressive symptoms scale (dimensional) and DSM major depressive episodes (categorical). Both sets of dimensional and categorical models were compared in terms of their abilities to predict various clinically relevant outcomes (psychiatric diagnoses and impairment).

RESULTS

Factor analyses suggested a two-factor model ('cognitive-affective' and 'somatic' symptoms) and latent class analyses suggested a three-class model ('severe depression', 'moderate depression' and 'cognitive-affective distress'). In predictive analyses that simultaneously included dimensional and categorical models as predictors, the dimensional models remained significant unique predictors of outcomes while the categorical models did not.

CONCLUSIONS

Both dimensional models provided superior predictive validity relative to their categorical counterparts. These results provide construct validity evidence for the dimensional findings from our previous taxometric study and thus inspire confidence in dimensional conceptualizations of depression. It remains for future research to evaluate the construct validity of the taxonic solutions reported in the literature.

A taxometric investigation of DSM-IV major depression in a large outpatient sample: interpretable structural results depend on the mode of assessment

Most taxometric studies of depressive constructs have drawn indicators from self-report instruments that do not bear directly on the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV) diagnostic construct of major depressive disorder (MDD). The present study examined the latent structure of MDD using indicator sets constructed from a semistructured clinical interview, self-report questionnaires, and a combination of the two. Taxometric analyses were performed in a large sample of outpatients with primary mood or anxiety disorders. For clinical rating data, results were more consistent with taxonic than dimensional structure, an interpretation supported by additional data obtained from 27 independent raters and objective indices of curve fit. Questionnaire indicators yielded inconclusive results, and combined rating- questionnaire indicators yielded results suggestive of taxonic structure. The findings highlight the importance of assessment in the study of a construct's latent structure and extend recent findings suggesting that MDD may be taxonic.

Phenomics: the systematic study of phenotypes on a genome-wide scale

Phenomics is an emerging transdiscipline dedicated to the systematic study of phenotypes on a genome-wide scale. New methods for high-throughput genotyping have changed the priority for biomedical research to phenotyping, but the human phenome is vast and its dimensionality remains unknown. Phenomics research strategies capable of linking genetic variation to public health concerns need to prioritize development of mechanistic frameworks that relate neural systems functioning to human behavior. New approaches to phenotype definition will benefit from crossing neuropsychiatric syndromal boundaries, and defining phenotypic features across multiple levels of expression from proteome to syndrome. The demand for high throughput phenotyping may stimulate a migration from conventional laboratory to web-based assessment of behavior, and this offers the promise of dynamic phenotyping-the iterative refinement of phenotype assays based on prior genotype-phenotype associations. Phenotypes that can be studied across species may provide greatest traction, particularly given rapid development in transgenic modeling. Phenomics research demands vertically integrated research teams, novel analytic strategies and informatics infrastructure to help manage complexity. The Consortium for Neuropsychiatric Phenomics at UCLA has been supported by the National Institutes of Health Roadmap Initiative to illustrate these principles, and is developing applications that may help investigators assemble, visualize, and ultimately test multi-level phenomics hypotheses. As the transdiscipline of phenomics matures, and work is extended to large-scale international collaborations, there is promise that systematic new knowledge bases will help fulfill the promise of personalized medicine and the rational diagnosis and treatment of neuropsychiatric syndromes.

A brief taxometrics primer

Taxometric procedures provide an empirical means of determining which psychiatric disorders are typologically distinct from normal behavioral functioning. Although most disorders reflect extremes along continuously distributed behavioral traits, identifying those that are discrete has important implications for accurate diagnosis, effective treatment, early identification of risk, and improved understanding of etiology. This article provides (a) brief descriptions of the conceptual bases of several taxometric procedures, (b) example analyses using simulated data, and (c) strategies for avoiding common pitfalls that are often observed in taxometrics research. To date, most taxometrics studies have appeared in the adult psychopathology literature. It is hoped that this primer will encourage interested readers to extend taxometrics research to child and adolescent populations.

Familial and temperamental predictors of resilience in children at risk for conduct disorder and depression

In this study, we evaluated predictors of resilience among 8- to 12-year-old children recruited from primarily low socioeconomic status neighborhoods, 117 of whom suffered from clinical levels of conduct problems and/or depression, and 63 of whom suffered from no significant symptoms. Tests of interactions were conducted between (a) paternal antisocial behavior and maternal depression and (b) several physiological indices of child temperament and emotionality in predicting (c) children's conduct problems and depression. Both internalizing and externalizing outcomes among children were associated specifically with maternal melancholic depression, and not with nonmelancholic depression. In addition, low levels of respiratory sinus arrhythmia (RSA) among children conferred significant risk for depression, regardless of maternal melancholia, whereas high RSA offered partial protection. Furthermore, high levels of maternal melancholia conferred significant risk for child depression, regardless of paternal antisocial behavior, whereas low levels of maternal melancholia offered partial protection. Finally, low levels of electrodermal responding (EDR) conferred significant risk for conduct problems, regardless of paternal antisocial behavior, whereas high EDR offered partial protection. None of the identified protective factors offered complete immunity from psychopathology. These findings underscore the complexity of resilience and resilience-related processes, and suggest several potential avenues for future longitudinal research.

Does dopamine dysfunction drive depression?

OBJECTIVE

To examine the evidence that dopamine (DA) dysfunction contributes to melancholic depression.

METHOD

Database (EMBASE, PsychLit and MEDLINE) searches using relevant key words were conducted and citations were scrutinized.

RESULTS

In this paper, we assume that the definition of melancholia is contingent upon the presence of psychomotor disturbance (PMD). In melancholic depression PMD comprises both a cognitive and motor component and DA is found to be important in both. DA neurotransmission modulates cognition in particular in attention, adaptation and motivational processes and has a pivotal role in motor function.

CONCLUSION

DA is a credible aetiological candidate for the PMD in melancholic depression. However, melancholia needs first to be characterized both clinically and in terms of its pathophysiology. In this regard, illnesses such as bipolar depression and Parkinson's disease warrant consideration as they provide suitable models of both the cognitive and motor aspects of PMD, and hold the necessary markers to better define melancholia.

Resurrecting melancholia

OBJECTIVE

To define melancholia as a distinct mood disorder, identified by unremitting depressed mood, vegetative dysfunction, and psychomotor disturbances, verifiable by neuroendocrine tests, and treatable by electroconvulsive therapy and tricyclic antidepressants.

METHOD

A review of the literature of two centuries finds descriptions of severe mood disorders, either depression or mania or circular, defined as 'melancholia.' In the 1980 diagnostic revision (DSM-III), melancholia was relegated to a features specifier only.

RESULTS

DSM classification criteria develop heterogeneous patient samples that are neither guides to prognosis nor to treatment response, and confound studies of pathophysiology. Within the large population of mood disorders, a syndrome of melancholia is identifiable by specific behaviors, vegetative signs, and validated by neuroendocrine abnormalities (cortisolemia). Populations so identified are clinically homogeneous and have improved treatment responses. Patients meeting criteria for melancholia are now identified as psychotic depressed, geriatric depressed, postpartum psychosis, and pharmacotherapy resistant.

CONCLUSION

The review supports the establishment of melancholia by empirically derived criteria rather than by a checklist is an alternative to the major depression choice and offers an improved model for psychiatric classification.

Diagnosing major depressive disorder XI: a taxometric investigation of the structure underlying DSM-IV symptoms

Psychopathologists have long debated the latent structure of mental disorders, and a number of researchers have suggested that depression may be best characterized as a continuous, rather than categorical, phenomenon. Nonetheless, attention has been drawn to limitations permeating existing research and the need for studies using more appropriate statistical methods developed expressly to tease apart taxonic (categorical) and dimensional (continuous) structural models. The present study examined the structure underlying the DSM-IV symptoms of major depressive disorder in a large outpatient sample rigorously assessed using semistructured clinical interviews. The results of a series of taxometric procedures and consistency tests supported a taxonic structural model, consistent with the only previous taxometric study of DSM-IV symptoms in an adult outpatient sample. In addition to the need for further replication and clarification, these results have implications for the assessment and diagnosis of major depressive disorder. Suggestions for several additional avenues of research are discussed.

The latent structure of attention-deficit/hyperactivity disorder: a taxometric analysis

OBJECTIVE

To test whether the latent structure of attention deficit/hyperactivity disorder (ADHD) is best understood as categorical or dimensional in samples of 1774 children (aged 6-12 years) and 1222 adolescents (aged 13-17 years) drawn from an Australian epidemiological study.

METHOD

Two taxometric procedures (MAXEIG and MAMBAC) examined ADHD symptom measures assessed by diagnostic interview and parental ratings.

RESULTS

Consistent with behavioural genetic research, findings fail to support the view that a latent category underpins ADHD.

CONCLUSIONS

ADHD is best modelled as a continuum among both children and adolescents, and no discrete dysfunction can therefore be assumed to cause it. The placement of the diagnostic threshold should therefore be decided on pragmatic grounds (e.g. impairment or need for treatment).

A Taxometric Study of the Center for Epidemiological Studies Depression Scale

The authors assessed the latent structure of depressive symptoms as measured by the Center for Epidemiological Studies Depression Scale (CES-D; L. S. Radloff, 1977). By using taxometric procedures, the authors conducted analyses of CES-D data obtained from a large college student population. These procedures incorporated strategies for interpreting analyses of skewed indicators and small putative taxa. The authors hypothesized that CES-D total scores would be represented as a dimension, with a taxonic distribution of a factor incorporating somatic symptoms. Results indicated that all CES-D factors, including the factor composed of somatic complaints, were dimensional. Administration of the Diagnostic Interview Schedule-IV (L. N. Robins, L. Marcus, & W. Reich, 1996) to one quarter of the participants indicated that the CES-D was effective in identifying cases of current or recent clinical depression. Evidence of the dimensionality of CES-D indicators in a student population is consistent with a continuity view of depressive symptoms.

A taxometric investigation of unipolar depression in the national comorbidity survey

Ongoing debate has questioned whether unipolar depression is a dimensional or categorical phenomenon. Although past studies using taxometric methods have supported a dimensional interpretation, each has suffered from methodological limitations. The present study was designed to overcome these limitations through reanalysis of the National Comorbidity Survey. Two indicator sets were constructed from the depression-relevant questions of the Composite International Diagnostic Interview. Participants who endorsed the lifetime occurrence of significant depressed mood or anhedonia (n=4,577) were submitted to 2 nonredundant taxometric procedures (maximum eigenvalue and means above minus below a cut), additional consistency tests, and recently developed simulation techniques. All results converged on a dimensional solution. The implications of these findings on assessment, treatment, and research design are discussed.

Can sample-specific simulations help detect low base-rate taxonicity?

The authors examined the role of the sample-specific simulations (SSS; A. M. Ruscio & J. Ruscio, 2002; J. Ruscio & A. M. Ruscio, 2004) procedure in detecting low base-rate taxa that might otherwise prove elusive. The procedure preserved key distributional characteristics for moderate to high base-rate taxa, but it performed inadequately for low base-rate taxa, with low to moderate nuisance covariance, decreasing indicator validity, and increasing average nuisance covariance. Visual inspection of the curves produced by the SSS procedure, combined with the expectation that the inchworm test should produce a clear peak for low base-rate taxonic samples, led to inappropriate conclusions about the suitability of data. The authors speculate that examination of low base-rate taxa using SSS may require other algorithms for generating comparison distributions, consideration of the shape of the whole curve, and/or relaxation of the expectation that a clear peak will emerge with the inchworm test.

Toward guidelines for evidence-based assessment of depression in children and adolescents

We aim to provide a starting point toward the development of an evidence-based assessment of depression in children and adolescents. We begin by discussing issues relevant to the diagnosis and classification of child and adolescent depression. Next, we review the prevalence, selected clinical correlates, course, and treatment of juvenile depression. Along with some general considerations in assessment, we discuss specific approaches to assessing depression in youth (i.e., interviews, rating scales) and briefly summarize evidence on the reliability and validity of a few selected instruments. In addition, we touch on the assessment of several other constructs that are important in a comprehensive evaluation of depression (i.e., social functioning, life stress, and family history of psychopathology). Last, we highlight areas in which further research is necessary and conclude with some broad recommendations for clinical practice given the current state of the knowledge.

Is Depression Best Viewed as a Continuum or Discrete Category? A Taxometric Analysis of Childhood and Adolescent Depression in a Population-Based Sample

The authors examined the latent structure of depression in a population-based sample of children and adolescents. Youth's self-reports and parents' reports of the youth's Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV; American Psychiatric Association, 1994) major depressive symptoms were assessed via a structured clinical interview. The authors used Meehl's (1995) taxometric procedures to discern whether youth depression is dimensional or categorical. Taxometric analyses that explicitly took into account the skewness of depressive symptoms suggested that depression is a dimensional, not categorical, construct. The dimensional structure of depression was obtained for all of the DSM-IV major depressive symptoms as well as for different domains of depression (emotional distress symptoms and vegetative, involuntary defeat symptoms), youth and parent reports, and different subsamples (i.e., boys vs. girls and younger vs. older youth).

Evidence-based assessment of depression in adults

From diverse perspectives, there is little doubt that depressive symptoms cohere to form a valid and distinct syndrome. Research indicates that an evidence-based assessment of depression would include (a) measures with adequate psychometric properties; (b) adequate coverage of symptoms; (c) adequate coverage of depressed mood, anhedonia, and suicidality; (d) an approach to suicidality that distinguishes between resolved plans and preparations and desire and ideation; (e) assessment of the atypical, seasonal, and melancholic subtypes; (f) parameters of course and chronicity; and (g) comorbidity and bipolarity. These complexities need to be accounted for when certain assessment approaches are preferred, and when ambiguity exists regarding the categorical versus dimensional nature of depression, and whether and when clinician ratings outperform self-report. The authors conclude that no one extant procedure is ideal and suggest that the combination of certain interviews and self-report scales represents the state of the art for evidence-based assessment of depression.

Cognitive Vulnerability to Depression: A Taxometric Analysis

Although there is increasing support for the hypothesis that negative cognitive styles contribute vulnerability to depression, it remains unclear how best to conceptualize the heterogeneity in cognitive vulnerability to depression. Specifically, does this heterogeneity reflect quantitative or qualitative differences among individuals? The goal of this study was to address this question by examining whether the underlying structure of cognitive vulnerability to depression is best conceptualized as dimensional or categorical. Taxometric analyses provided consistent support for the dimensional nature of negative cognitive styles. It appears, therefore, that cognitive vulnerability to depression is best conceptualized as a dimensional construct, present to a greater or lesser extent in all individuals. Despite this, the strength of the relationship between negative cognitive styles and depressive symptoms does appear to vary as a function of where along the cognitive style continuum one falls.

Categorical versus dimensional models of mental disorder: the taxometric evidence

OBJECTIVE

To review studies of the categorical versus dimensional status of mental disorders that employ taxometric methodology.

METHOD

A comprehensive qualitative review of all published taxometric studies of psychopathology.

RESULTS

Categorical and dimensional models each receive well-replicated support for some groups of mental disorders. Studies favour categorical models for melancholia, eating disorders, pathological dissociation, and schizotypal and antisocial personality disorders. Dimensional models tend to be favoured for the broad neurotic spectrum--general depression, generalized anxiety, posttraumatic stress disorder--and for borderline personality disorder.

CONCLUSIONS

Taxometric research clarifies the latent structure of psychopathology in ways that have implications for the classification, assessment, explanation and conceptualization of mental disorder.

Is depression taxonic, dimensional, or both?

The current investigation examines the potential importance of item selection in the ongoing discussion regarding the taxonicity of depression. Following J. C. Coyne (1994), we contrast the taxonicity of "distress" with the taxonicity of a syndrome more focused on somatic symptoms (i.e., the involuntary defeat syndrome). Using 4 samples of 984 undergraduates, we first replicate the J. Ruscio and A. M. Ruscio (2000) results by showing that distress item indicators are dimensional. We then demonstrate taxonicity using items focused on somatic symptoms and reflective of disruption of multiple homeostatic mechanisms. Results suggest that item selection is central to the determination of taxonicity in depression.