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

Revisiting the theoretical and methodological foundations of depression measurement

Depressive disorders are among the leading causes of global disease burden, but there has been limited progress in understanding the causes and treatments for these disorders. In this Perspective, we suggest that such progress crucially depends on our ability to measure depression. We review the many problems with depression measurement, including limited evidence of validity and reliability. These issues raise grave concerns about common uses of depression measures, such as diagnosis or tracking treatment progress. We argue that shortcomings arise because depression measurement rests on shaky methodological and theoretical foundations. Moving forward, we need to break with the field's tradition that has, for decades, divorced theories about depression from how we measure it. Instead, we suggest that epistemic iteration, an iterative exchange between theory and measurement, provides a crucial avenue for depression measurement to progress.

Using major depression polygenic risk scores to explore the depressive symptom continuum

BACKGROUND

Major depression (MD) is often characterised as a categorical disorder; however, observational studies comparing sub-threshold and clinical depression suggest MD is continuous. Many of these studies do not explore the full continuum and are yet to consider genetics as a risk factor. This study sought to understand if polygenic risk for MD could provide insight into the continuous nature of depression.

METHODS

Factor analysis on symptom-level data from the UK Biobank (N = 148 957) was used to derive continuous depression phenotypes which were tested for association with polygenic risk scores (PRS) for a categorical definition of MD (N = 119 692).

RESULTS

Confirmatory factor analysis showed a five-factor hierarchical model, incorporating 15 of the original 18 items taken from the PHQ-9, GAD-7 and subjective well-being questionnaires, produced good fit to the observed covariance matrix (CFI = 0.992, TLI = 0.99, RMSEA = 0.038, SRMR = 0.031). MD PRS associated with each factor score (standardised β range: 0.057-0.064) and the association remained when the sample was stratified into case- and control-only subsets. The case-only subset had an increased association compared to controls for all factors, shown via a significant interaction between lifetime MD diagnosis and MD PRS (p value range: 2.23 × 10^-3-3.94 × 10^-7).

CONCLUSIONS

An association between MD PRS and a continuous phenotype of depressive symptoms in case- and control-only subsets provides support against a purely categorical phenotype; indicating further insights into MD can be obtained when this within-group variation is considered. The stronger association within cases suggests this variation may be of particular importance.

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.

The latent structure of depression symptoms and suicidal thoughts in Brazilian youths

BACKGROUND

Many studies have investigated the existence of discrete groups comprising the clinical concept of depression. Nevertheless, identifying true latent depression groups might require the inclusion of indicators of severe manifestations of depression, such as suicidal thoughts, in the analysis. Another issue is that relatively few studies have addressed the latent structure of depression in children and adolescents from Latin American cultures.

METHODS

In the present study, we combined latent profile and taxometric analysis to investigate the latent structure underlying depression symptoms (negative emotionality and low positive emotionality indicators) and suicidal thoughts in four aggregated Brazilian youth samples (total N = 2587; mean age = 12.86 years; SD = 2.60; 50.8% females).

RESULTS

Latent profile analysis indicated five classes that clearly represented distinct levels on a continuum of depression. However, taxometric results were ambiguous with regard to highlighting depression as a purely dimensional or categorical latent entity (mean CCFI = 0.497).

LIMITATIONS

The use of few indicators from a single instrument, the potential heterogeneity in the clinical group, and the non-random nature of the samples included in the study.

CONCLUSION

The mixed findings support the existence of a dimension of depression, as well as latent classes of individuals. Factor mixture models are discussed as a strategy for further exploring the nature of depression among young people.

The severity of psychiatric disorders

The issue of the severity of psychiatric disorders has great clinical importance. For example, severity influences decisions about level of care, and affects decisions to seek government assistance due to psychiatric disability. Controversy exists as to the efficacy of antidepressants across the spectrum of depression severity, and whether patients with severe depression should be preferentially treated with medication rather than psychotherapy. Measures of severity are used to evaluate outcome in treatment studies and may be used as meaningful endpoints in clinical practice. But, what does it mean to say that someone has a severe illness? Does severity refer to the number of symptoms a patient is experiencing? To the intensity of the symptoms? To symptom frequency or persistence? To the impact of symptoms on functioning or on quality of life? To the likelihood of the illness resulting in permanent disability or death? Putting aside the issue of how severity should be operationalized, another consideration is whether severity should be conceptualized similarly for all illnesses or be disorder specific. In this paper, we examine how severity is characterized in research and contemporary psychiatric diagnostic systems, with a special focus on depression and personality disorders. Our review shows that the DSM-5 has defined the severity of various disorders in different ways, and that researchers have adopted a myriad of ways of defining severity for both depression and personality disorders, although the severity of the former was predominantly defined according to scores on symptom rating scales, whereas the severity of the latter was often linked with impairments in functioning. Because the functional impact of symptom-defined disorders depends on factors extrinsic to those disorders, such as self-efficacy, resilience, coping ability, social support, cultural and social expectations, as well as the responsibilities related to one's primary role function and the availability of others to assume those responsibilities, we argue that the severity of such disorders should be defined independently from functional impairment.

Is Adolescent Suicidal Ideation Continuous or Categorical? A Taxometric Analysis

Despite the strong association between suicidal ideation and suicidal behavior, a relative minority of ideators transition to attempting suicide. Clarifying the latent structure of suicidal ideation has direct implications for theory, as well as suicidal risk assessment and prevention efforts. Taxometric analysis is a statistical technique specifically designed to assess whether a latent construct is taxonic (i.e., categorical) or continuous (i.e., dimensional) in nature. Although this statistical approach has been increasingly used over the past decade to elucidate the latent structure of various forms of psychopathology and related risk factors, there are no taxometric studies to date of suicidal ideation. The aim of the current project is to apply taxometric methods to a sample of clinically depressed, treatment-seeking adolescents (n = 334). Current suicidal ideation was measured using the Suicidal Ideation Questionnaire-Jr., (SIQ-Jr.). The results of two mathematically non-redundant taxometric approaches (i.e., MAXEIG and L-Mode) are consistent with a continuous latent structure for suicidal ideation. The current findings suggest that suicidal ideation in depressed adolescents is dimensional. The implication of these findings for research, theory, and suicidal risk assessment strategies are discussed.

Evidence for the continuous latent structure of mania and depression in out-patients with bipolar disorder: results from the Systematic Treatment Enhancement Program for Bipolar Disorder (STEP-BD)

BACKGROUND

Evidence supporting the continuous latent structure of mood phenomena has not been incorporated into psychiatric diagnostic systems, in part because the evidence has been incomplete. For example, no studies have investigated the boundary between 'sick' and 'well' periods in individuals with bipolar disorder, despite agreement that characterization of mood disorders as having a discrete episodic course is inaccurate. The present study examined the validity of mood episode symptom thresholds in out-patients with bipolar disorder using multiple methodologies: taxometrics and information-theoretic latent distribution modeling (ITLDM), to evaluate the continuity/discontinuity of mood symptoms; and structural equation mixture modeling (SEMM), to evaluate the continuity/discontinuity of associations between mood symptoms and general functioning.

METHOD

A total of 3721 out-patients with bipolar disorder from the Systematic Treatment Enhancement Program for Bipolar Disorder (STEP-BD) were available for analysis. Data were collected at participants' baseline STEP-BD visit. Taxometric [maximum covariance/means above minus below a cut (MAXCOV/MAMBAC) with simulated comparison data], ITLDM and SEMM methods were applied twice, once to the Montgomery-Åsberg Depression Rating Scale and again to the Young Mania Rating Scale.

RESULTS

Taxometric results unequivocally supported a continuous interpretation of the data. ITLDM results favored many valued 'discrete metrical' models, suggesting that mood symptoms have continuous, but potentially non-normally distributed, latent structures in out-patients with bipolar disorder. Finally, SEMM results demonstrated that latent associations between mood symptoms and general functioning were linear.

CONCLUSIONS

Results from the present study argue against the validity of DSM mood episode thresholds and argue for a graded continuum of care of bipolar symptom management.

Problematic assumptions have slowed down depression research: why symptoms, not syndromes are the way forward

Major depression (MD) is a highly heterogeneous diagnostic category. Diverse symptoms such as sad mood, anhedonia, and fatigue are routinely added to an unweighted sum-score, and cutoffs are used to distinguish between depressed participants and healthy controls. Researchers then investigate outcome variables like MD risk factors, biomarkers, and treatment response in such samples. These practices presuppose that (1) depression is a discrete condition, and that (2) symptoms are interchangeable indicators of this latent disorder. Here I review these two assumptions, elucidate their historical roots, show how deeply engrained they are in psychological and psychiatric research, and document that they contrast with evidence. Depression is not a consistent syndrome with clearly demarcated boundaries, and depression symptoms are not interchangeable indicators of an underlying disorder. Current research practices lump individuals with very different problems into one category, which has contributed to the remarkably slow progress in key research domains such as the development of efficacious antidepressants or the identification of biomarkers for depression. The recently proposed network framework offers an alternative to the problematic assumptions. MD is not understood as a distinct condition, but as heterogeneous symptom cluster that substantially overlaps with other syndromes such as anxiety disorders. MD is not framed as an underlying disease with a number of equivalent indicators, but as a network of symptoms that have direct causal influence on each other: insomnia can cause fatigue which then triggers concentration and psychomotor problems. This approach offers new opportunities for constructing an empirically based classification system and has broad implications for future research.

Severity classification on the Hamilton Depression Rating Scale

BACKGROUND

Symptom severity as a moderator of treatment response has been the subject of debate over the past 20 years. Each of the meta- and mega-analyses examining the treatment significance of depression severity used the Hamilton Depression Rating Scale (HAMD), wholly, or in part, to define severity, though the cutoff used to define severe depression varied. There is limited empirical research establishing cutoff scores for bands of severity on the HAMD. The goal of the study is to empirically establish cutoff scores on the HAMD in their allocation of patients to severity groups.

METHODS

Six hundred twenty-seven outpatients with current major depressive disorder were evaluated with a semi-structured diagnostic interview. Scores on the 17-item HAMD were derived from ratings according to the conversion method described by Endicott et al. (1981). The patients were also rated on the Clinical Global Index of Severity (CGI). Receiver operating curves were computed to identify the cutoff that optimally discriminated between patients with mild vs. moderate and moderate vs. severe depression.

RESULTS

HAMD scores were significantly lower in patients with mild depression than patients with moderate depression, and patients with moderate depression scored significantly lower than patients with severe depression. The cutoff score on the HAMD that maximized the sum of sensitivity and specificity was 17 for the comparison of mild vs. moderate depression and 24 for the comparison of moderate vs. severe depression.

LIMITATIONS

The present study was conducted in a single outpatient practice in which the majority of patients were white, female, and had health insurance. Although the study was limited to a single site, a strength of the recruitment procedure was that the sample was not selected for participation in a treatment study, and exclusion and inclusion criteria did not reduce the representativeness of the patient groups. The analyses were based on HAMD scores extracted from ratings on the SADS. However, we used Endicott et al.'s (1981) empirically established formula for deriving a HAMD score from SADS ratings, and our results concurred with other small studies of the mean and median HAMD scores in severity groups.

CONCLUSIONS

Based on this large study of psychiatric outpatients with major depressive disorder we recommend the following severity ranges for the HAMD: no depression (0-7); mild depression (8-16); moderate depression (17-23); and severe depression (≥24).

Factor mixture analysis of DSM-IV symptoms of major depression in a treatment seeking clinical population

BACKGROUND

There is a paucity of empirical studies examining the latent structure of depression symptoms within clinical populations.

OBJECTIVE

The current study aimed to evaluate the latent structure of DSM-IV major depression utilising dimensional, categorical, and hybrid models of dimensional and categorical latent variables in a large treatment-seeking population.

METHODS

Latent class models, latent factor models, and factor mixture models were fit to data from 1165 patients currently undergoing online treatment for depression.

RESULTS

Model fit statistics indicated that a two-factor model fit the data the best when compared to a one-factor model, latent class models, and factor mixture models.

CONCLUSIONS

The current study suggests that the structure of depression consists of two underlying dimensions of depression severity when compared to categorical or a mixture of both categorical and dimensional structures. For clinical samples, the two latent factors represent psychological and somatic symptoms.

Neuropsychological correlates of symptom dimensions in inpatients with major depressive disorder

Symptoms of major depressive disorder (MDD) manifest variably across individuals. Accordingly, recent models of the disorder imply that MDD may be characterized according to independent symptom dimensions. In particular, several studies reveal that depression may be characterized along dimensions of negative affect, agitation and hostility, and lassitude and malaise. No research has examined the relationship between these dimensions and neuropsychological function. Towards this end, 133 in patients with unipolar MDD and 17 people without psychiatric illness were administered a brief battery of neuropsychological tests and the MMPI-2. Paralleling earlier research, principal component analysis of the MMPI-2 revealed symptom dimensions of negative affect, agitation, and lassitude and malaise. Multiple regression analyses showed that the negative affect and agitation dimensions accounted for significant variance on measures of executive function, speed of information processing, new learning, dexterity, and overall impairment. Lassitude and malaise failed to correspond with neuropsychological performance. Implications of these data for clinical practice and neural models of MDD are discussed.

Should criteria be specified for depressive disorder not otherwise specified?

BACKGROUND

Many patients have clinically significant symptoms of depression that do not meet the DSM-IV diagnostic thresholds for major depressive disorder (MDD) or dysthymic disorder. DSM-IV does not specify criteria for depressive disorder not otherwise specified (DDNOS). While it is not surprising that research on subthreshold depression has used diverse criteria, some consensus has emerged to define minor depression analogous to MDD, though requiring fewer than the 5 symptoms required to diagnose MDD. In the present report from the Rhode Island Methods to Improve Diagnostic Assessment and Services (MIDAS) project, we examined how many patients diagnosed with DDNOS met the DSM-IV proposed research criteria for minor depression, and we compared the demographic and clinical profiles of patients diagnosed with DDNOS who did and did not meet the criteria for minor depression

METHODS

Three thousand four hundred psychiatric patients presenting to the Rhode Island Hospital outpatient practice were evaluated with semi-structured diagnostic interviews for DSM-IV Axis I and Axis II disorders and measures of psychosocial morbidity.

RESULTS

More than 6% of the 3400 patients were diagnosed with DDNOS (n=227). Only a minority of the patients with DDNOS met the criteria for minor depression (39.8%). There was no difference between patients with "subthreshold" depression who did and did not meet the DSM-IV research criteria for minor depression in demographic characteristics, the prevalence of comorbid Axis I or Axis II disorders, history of major depressive disorder, and family history of depression.

LIMITATIONS

The present study was conducted in a single outpatient practice in which the majority of patients were white, female, and had health insurance. Although the study was limited to a single site, a strength of the recruitment procedure was that the sample was not selected for participation in a treatment study, and exclusion and inclusion criteria did not reduce the representativeness of the patient groups. While we examined a number of validators, we did not systematically record the treatment the patients received and the outcome of treatment.

CONCLUSIONS

Amongst psychiatric outpatients with clinically significant depression not meeting criteria for MDD or dysthymic disorder, there was little difference between patients who did and did not meet the DSM-IV research criteria for minor depressive disorder.

Taxometric analysis of DSM-IV and DSM-5 alcohol use disorders

BACKGROUND

With preparations currently being made for the Diagnostic and Statistical Manual of Mental Disorders-5th Edition (DSM-5), one prominent issue to resolve is whether alcohol use disorders are better represented as discrete categorical entities or as a dimensional construct. The purpose of this study was to investigate the latent structure of DSM-4th edition (DSM-IV) and proposed DSM-5 alcohol use disorders.

METHODS

The study used the Wave 2 National Epidemiologic Survey on Alcohol and Related Conditions (NESARC) to conduct taxometric analyses of DSM-IV and DSM-5 alcohol use disorders defined by different thresholds to determine the taxonic or dimensional structure underlying the disorders.

RESULTS

DSM-IV and DSM-5 alcohol abuse and dependence criteria with 3+ thresholds demonstrated a dimensional structure. Corresponding thresholds with 4+ criteria were clearly taxonic, as were thresholds defined by cut-offs of 5+ and 6+ criteria.

CONCLUSIONS

DSM-IV and DSM-5 alcohol use disorders demonstrated a hybrid taxonic-dimensional structure. That is, DSM-IV and DSM-5 alcohol use disorders may be taxonically distinct compared to no disorder if defined by a threshold of 4 or more criteria. However, there may be dimensional variation remaining among non-problematic to subclinical cases. A careful and systematic program of structural research using taxometric and psychometric procedures is warranted.

Determining severity subtypes of depression with a self-report questionnaire

The American Psychiatric Association's recently revised guidelines for the treatment of major depressive disorder indicated that it is important to consider symptom severity in initial treatment selection. In the present report from the Rhode Island Methods to Improve Diagnostic Assessment and Services (MIDAS) project, we conducted two studies of psychiatric outpatients examining the correlates of severity classification based on a self-report depression scale. The first sample consisted of 470 depressed outpatients who completed the Clinically Useful Depression Outcome Scale (CUDOS) and measures of psychosocial morbidity at the time of presentation. The second sample consisted of 112 depressed outpatients who completed the CUDOS and were evaluated with the Hamilton Depression Rating Scale at baseline and after 3 months of treatment. Compared to mildly depressed patients, moderately depressed patients reported significantly more psychosocial morbidity across all functional domains. The same differences were found between moderately and severely depressed patients. Greater severity of depression was associated with lower rates of response and remission. The results of the present studies suggest that a self-report depression questionnaire can validly subtype depressed patients according to gradations of severity.

Are increased weight and appetite useful indicators of depression in children and adolescents?

During childhood and adolescence, physiological, psychological, and behavioral processes strongly promote weight gain and increased appetite while also inhibiting weight loss and decreased appetite. The Diagnostic and Statistical Manual-IV (DSM-IV) treats both weight-gain/increased-appetite and weight-loss/decreased-appetite as symptoms of major depression during these developmental periods, despite the fact that one complements typical development and the other opposes it. To disentangle the developmental versus pathological correlates of weight and appetite disturbance in younger age groups, the current study examined symptoms of depression in an aggregated sample of 2307 children and adolescents, 47.25% of whom met criteria for major depressive disorder. A multigroup, multidimensional item response theory model generated three key results. First, weight loss and decreased appetite loaded strongly onto a general depression dimension; in contrast, weight gain and increased appetite did not. Instead, weight gain and increased appetite loaded onto a separate dimension that did not correlate strongly with general depression. Second, inclusion or exclusion of weight gain and increased appetite affected neither the nature of the general depression dimension nor the fidelity of major depressive disorder diagnosis. Third, the general depression dimension and the weight-gain/increased-appetite dimension showed different patterns across age and gender. In child and adolescent populations, these results call into question the utility of weight gain and increased appetite as indicators of depression. This has serious implications for the diagnostic criteria of depression in children and adolescents. These findings inform a revision of the DSM, with implications for the diagnosis of depression in this age group and for research on depression.

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.

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.

Evidence for the continuous latent structure of mania in the Epidemiologic Catchment Area from multiple latent structure and construct validation methodologies

BACKGROUND

Although psychiatric diagnostic systems have conceptualized mania as a discrete phenomenon, appropriate latent structure investigations testing this conceptualization are lacking. In contrast to these diagnostic systems, several influential theories of mania have suggested a continuous conceptualization. The present study examined whether mania has a continuous or discrete latent structure using a comprehensive approach including taxometric, information-theoretic latent distribution modeling (ITLDM) and predictive validity methodologies in the Epidemiologic Catchment Area (ECA) study.

METHOD

Eight dichotomous manic symptom items were submitted to a variety of latent structural analyses, including factor analyses, taxometric procedures and ITLDM, in 10105 ECA community participants. In addition, a variety of continuous and discrete models of mania were compared in terms of their relative abilities to predict outcomes (i.e. health service utilization, internalizing and externalizing disorders, and suicidal behavior).

RESULTS

Taxometric and ITLDM analyses consistently supported a continuous conceptualization of mania. In ITLDM analyses, a continuous model of mania demonstrated 6.52:1 odds over the best-fitting latent class model (LCM) of mania. Factor analyses suggested that the continuous structure of mania was best represented by a single latent factor. Predictive validity analyses demonstrated a consistent superior ability of continuous models of mania relative to discrete models.

CONCLUSIONS

The present study provided three independent lines of support for a continuous conceptualization of mania. The implications of a continuous model of mania are discussed.

Dementia: continuum or distinct entity?

The latent structure of dementia was examined in a group of 10,775 older adults with indicators derived from a neuropsychological test battery. The author conducted taxometric analysis of these data using mean above minus below a cut, maximum covariance, and latent mode factor analysis and found results more consistent with dementia as a dimensional (lying along a continuum) than categorical (representing a distinct entity) construct. A second study conducted with a group of 2,375 adults whose ages ranged from 21 to 64 years produced similar results. These findings denote that dementia, as measured by deficits in episodic memory, attention and concentration, executive function, and language, differs quantitatively rather than qualitatively from the cognitive status of adults without dementia. The implications of these results for classification, assessment, etiology, and prevention are discussed.

A longitudinal investigation of the impact of life stress on HIV treatment adherence

Suboptimal antiretroviral adherence is associated with poorer HIV outcomes. Psychosocial factors, including life stress, depression and coping, may influence adherence behavior. This prospective investigation sought to examine the impact of life stress (acute life events, chronic stress, and perceived stress), depression, and coping style on adherence to HIV treatment regimes over time. Participants were 87 treatment-seeking HIV-infected individuals recruited from an urban HIV clinic. They completed clinician-administered interviews and self-report questionnaires at baseline and 3-month follow-up. Acute life events and chronic stress prospectively predicted decreases in treatment adherence more strongly among individuals in a major depressive episode (n = 21) compared to non-depressed individuals (n = 66). Coping style did not appear to be the mechanism by which life stress influenced adherence among depressed HIV-infected individuals. These findings demonstrate that life stress has toxic effects for depressed individuals and suggest that treatment adherence interventions with depressed individuals could be enhanced via development of stress management skills.

The structure of late-life depressive symptoms across a 20-year span: a taxometric investigation

Past studies of the underlying structure of depressive symptoms have yielded mixed results, with some studies supporting a continuous conceptualization and others supporting a categorical one. However, no study has examined this research question with an exclusively older adult sample, despite the potential uniqueness of late-life depressive symptoms. In the present study, the underlying structure of late-life depressive symptoms was examined among a sample of 1,289 individuals across 3 waves of data collection spanning 20 years. The authors employed a taxometric methodology using indicators of depression derived from the Research Diagnostic Criteria (R. L. Spitzer, J. Endicott, & E. Robins, 1978). Maximum eigenvalue analyses and inchworm consistency tests generally supported a categorical conceptualization and identified a group that was primarily characterized by thoughts about death and suicide. However, compared to a categorical depression variable, depressive symptoms treated continuously were generally better predictors of relevant criterion variables. These findings suggest that thoughts of death and suicide may characterize a specific type of late-life depression, yet a continuous conceptualization still typically maximizes the predictive utility of late-life depressive symptoms.

Minor and major depression in the general population: does dysfunctional thinking play a role?

BACKGROUND

Although most research suggests that minor depression is part of a depression continuum, conflicting results have also been found. Moreover, little is known about dysfunctional thinking in minor depression and how this varies along the continuum. Especially, research on the form of dysfunctional thinking (ie, extreme responding) is lacking. We have addressed these issues by reporting results from a large community sample.

METHODS

Demographic, clinical, and cognitive factors (ie, content and form of dysfunctional thinking) were compared between minor depression (ie, 2-4 symptoms), major depression with 5 to 6 symptoms, and major depression with 7 to 9 symptoms. A large community sample (N = 1129) was used. Differences between the 3 subgroups were examined as well as linear relations between number of symptoms and factors marking the severity.

RESULTS

Most demographic variables did not distinguish the 3 depression status categories from each other. Clinical and cognitive factors acted in synchrony with the depression continuum.

CONCLUSIONS

Minor depression should be considered as part of continuum together with major depression. Not only the content but also the form of dysfunctional thinking seems to play a major role in depression. Extreme positive responding is more prominent in mild depression, whereas more severely depressed individuals have a general tendency toward extreme negative responding. This finding, if replicated, may have important implications for the cognitive theory of 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.

A taxometric analysis of health anxiety

BACKGROUND

A long-standing issue in the health anxiety literature is the extent to which health anxiety is a dimensional or a categorical construct. This study explores this question directly using taxometric procedures.

METHOD

Seven hundred and eleven working adults completed an index of health anxiety [the Whiteley Index (WI)] and indicated their current health status. Data from those who were currently healthy (n=501) and receiving no medical treatment were examined using three taxometric procedures: mean above minus below a cut (MAMBAC), maximum eigenvalue (MAXEIGEN) and L-mode factor analysis (L-MODE).

RESULTS

Graphical representations (comparing actual to simulated data) and fit indices indicate that health anxiety is more accurately represented as a dimensional rather than a categorical construct.

CONCLUSIONS

Health anxiety is better represented as a dimensional construct. Implications for theory development and clinical practice are examined.

Depression in older adults

Depression is less prevalent among older adults than among younger adults, but it can have serious consequences. More than half of cases represent a first onset in later life. Although suicide rates in the elderly are declining, they are still higher than in younger adults and are more closely associated with depression. Depressed older adults are less likely to endorse affective symptoms and more likely to display cognitive changes, somatic symptoms, and loss of interest than are depressed younger adults. Risk factors leading to the development of late-life depression likely comprise complex interactions among genetic vulnerabilities, cognitive diathesis, age-associated neurobiological changes, and stressful events. Insomnia is an often overlooked risk factor for late-life depression. We suggest that a common pathway to depression in older adults, regardless of which predisposing risks are most prominent, may be curtailment of daily activities. Accompanying self-critical thinking may exacerbate and maintain a depressed state. Offsetting the increasing prevalence of certain risk factors in late life are age-related increases in psychological resilience. Other protective factors include higher education and socioeconomic status, engagement in valued activities, and religious or spiritual involvement. Treatments including behavioral therapy, cognitive-behavioral therapy, cognitive bibliotherapy, problem-solving therapy, brief psychodynamic therapy, and life review/reminiscence therapy are effective but are too infrequently used with older adults. Preventive interventions including education for individuals with chronic illness, behavioral activation, cognitive restructuring, problem-solving skills training, group support, and life review have also received support.

Categories and Dimensions Advancing Psychological Science Through the Study of Latent Structure

The distinction between categories and dimensions has important consequences for basic and applied science in many areas of psychological research. Decisions as to whether individuals should be assigned to groups or located along one or more continua often are based on personal preferences or discipline-specific measurement traditions, which can lead to the creation, use, or reification of spurious categories or dimensions. Methods for evaluating the latent structure of psychological constructs, using powerful and informative tests between competing models, are available. Rather than choosing on a priori grounds, investigators can perform structural research to evaluate the strength and consistency with which results tease apart categorical and dimensional models. Here, we review why researchers should make this distinction empirically, briefly discuss methods available for doing so, and describe the breadth of areas ripe for exploiting the largely untapped potential of structural research.

Taxometric investigation of depression: evidence of consistent latent structure across clinical and community samples

OBJECTIVE

Past taxometric studies of depression have yielded equivocal results. Diversity of sample type may provide one explanation for this. The aim of the present study was to examine the latent structure of depression across clinical and community samples using exactly the same taxometric procedures involving exactly the same indicators of depression.

METHOD

Two taxometric procedures, MAXEIG (maximum eigenvalue) and MAMBAC (mean above minus mean below a cut), were carried out on a clinical sample of 960 outpatients with mood and anxiety disorders. Simulated categorical and dimensional data sets as well as other consistency tests aided in the interpretation of the research data. Results were compared to a prior taxometric analysis in a community sample.

RESULTS

The results of the current taxometric analyses were consistent with a dimensional latent structure and were compatible with the findings from identical analyses in a community sample.

CONCLUSIONS

The findings of the current study highlight the importance of identifying factors that may contribute to, and explain, differences in the identified latent structure of depression.