Copyright 1991 by the American Psychological Association Inc. 002l-843X/91/i3.00

Journal of Abnormal Psychology 1991, Vol. 100, No. 3,399-406

Differentiation of Axis I and Axis II Disorders Trade Shea

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Thomas A. Widiger University of Kentucky

Brown University

The revised 3rd edition of the Diagnostic and Statistical Manual of Menial Disorders (American Psychiatric Association, 1987) distinguishes between Axis I and Axis II disorders: Axis II includes personality (and developmental) disorders, and all others are on Axis I. This distinction is often useful, but the reification of Axis I and II constructs through diagnostic criteriasets that demarcate categorically distinct entities is at times problematic. We review the issues of differentiating personality from Axis I disorders, specifically illustrated by schizotypal and schizophrenic disorders, borderline and mood disorders, antisocial and substance use disorders, and avoidant personality from social phobia. The options for addressing their differentiation include adding exclusion criteria, shifting the placement of disorders, deleting overlapping criteria, adding differentiating criteria, and converting to a dimensional format.

It is stated in the introduction to the revised third edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IH-R; American Psychiatric Association, 1987) that

role of biogenetic factors in their etiology, their responsivity to pharmacologic treatment, and the severity of dysfunction. The placement of the personality disorders on a separate axis

"there is no assumption that each mental disorder is a discrete

has stimulated considerable interest in the comorbidity of the

entity with sharp boundaries (discontinuity) between it and other mental disorders" (p. xxii). Nevertheless, categorical dis-

personality and Axis I disorders (Docherty, Fiester, & Shea, 1986; Widiger & Hyler, 1987). However, their differentiation is

tinctions are made for all of the mental disorder diagnoses. One of the more fundamental distinctions is between Axis I and Axis II disorders. Axis II includes the developmental and per-

often problematic and perhaps at times even illusory. We discuss in this article issues and options with respect to their differentiation. It is important to note, however, that the issues in

sonality disorders. All of the other diagnoses are placed on Axis I. The original purpose for placing the personality disorders on a separate axis was pragmatic, to encourage the consideration of comorbid personality disorders in the context of a more florid and immediately problematic mood, anxiety, or psy-

distinguishing the personality from mood, anxiety, impulse dyscontrol, and psychotic disorders would still be present whether they were placed on a separate axis or not. We begin with a brief overview of some of the more problematic boundary diagnoses and follow that with discussion of various options for addressing their differentiation.

chotic disorder (Frances, 1980; Spitzer, Williams, & Skodol, 1980). A more conceptual rationale was developed for the

Problematic Boundaries

DSM-III-R. "The disorders listed on Axis II ... generally begin in childhood or adolescence and persist in a stable form

The issues with regards to differentiation are particularly evi-

(without periods of remission or exacerbation) into adult life.

dent for four pairs of Axis II and Axis I disorders: schizotypal

With only a few exceptions (e.g., the Gender Identity Disorders and Paraphillas), these features are not characteristic of the Axis I disorders" (American Psychiatric Association, 1987, p.

substance use, and avoidant versus social phobia diagnoses. We briefly discuss each of these in turn.

versus schizophrenic, borderline versus mood, antisocial versus

16). Axis I and II disorders have also been distinguished (perhaps inappropriately, as Gunderson & Pollack, 1985, suggested) with respect to the pervasiveness of their phenomenology, the

Schizotypal and Schizophrenia The schizotypal personality disorder was a new addition to the DSM-HI (American Psychiatric Association, 1980). The

The views expressed in this article are those of the authors and do not represent the official positions of the American Psychiatric Association or its Task Force on DSM-IV. We express our appreciation to the John D. and Catherine T. MacArthur Foundation, whose sponsorship of conferences on personality and depression has contributed to the development of this article. We also express our appreciation to David H. Barlow, Scott Lilienfeld, and an anonymous reviewer for their helpful comments on an earlier version of the article. Correspondence concerning this article should be addressed to Thomas A. Widiger, 1 15 Kastle Hall, University of Kentucky, Lexington, Kentucky 40506-0044. 399

diagnosis was intended "to describe certain psychopathological characteristics that are usually stable over time and are assumed to be genetically related to a spectrum of disorders including chronic schizophrenia" (Spitzer, Endicott, & Gibbon, 1979, p. 17). Research into family history, biological markers, phenomenology, and treatment has consistently verified the association of schizotypal personality disorder to schizophrenia (Gunderson & Siever, 1985), confirming that schizotypal personality disorder may represent a phenomenological or biogenetic variant of schizophrenic pathology (Kety, 1985; Siever, Klar, & Coccaro, 1985). It has therefore been suggested moving

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THOMAS A. WIDIGER AND TRACIE SHEA

schizotypal personality disorder from Axis II to Axis 1 (Frances, 1980; Klerman, 1990; Rutter, 1987). Such a placement will be consistent not only with the research but also with earlier formulations of borderline schizophrenia (Kety, 1985) and DSMII (American Psychiatric Association, 1968) latent schizophrenia and with the forthcoming 10th edition of the International Classification of Diseases and Related Health Problems (JCD10: World Health Organization, 1990). Moving schizotypal personality disorder to Axis I is controversial, however, not only with respect to its status as a personality disorder (which we discuss later) but also with respect to its relation to other diagnoses within the schizophrenia spectrum. One cannot provide the DSM-HI-R diagnoses of schizophrenia, schizoaffective, or schizophreniform to the same patient (American Psychiatric Association, 1987) because these diagnoses concern alternative variations along a common spectrum of pathology. On the other hand, DSM-IH-R excludes the diagnosis of schizotypal personality disorder only when it occurs exclusively in the context of schizophrenia. Otherwise, both diagnoses can be given. However, to the extent that schizotypal personality disorder is a variant of schizophrenic pathology, it may never be meaningful to provide both diagnoses to the same patient, because the schizotypal personality disorder symptomatology may represent an extended prodromal or a residua! phase of the schizophrenia. There is no exclusion rule in DSMIII-R that prohibits the diagnosis of schizotypal personality disorder with schizophreniform, but this apparent comorbidity of two disorders may again be simply one disorder. Borderline and Mood Disorders Various studies have been concerned with the association of borderline personality disorder to the mood disorders and have addressed course, family history, pharmacotherapy, and biological markers (Ounderson & Elliott, 1985). To some this research has suggested that borderline personality disorder is a variant of a mood disorder rather than a personality disorder (Davis & Akiskal, 1986). Others, however, have argued that most of the association is due to the comorbidity of mood disorders in borderline subjects and not to the borderline personality disorder itself (Gunderson & Zanarini, 1989). Akiskal, Yerevanian, Davis, King, and Lemmi (1985) attempted to control for the presence of artifactual comorbid mood pathology by excluding from their study borderline patients who had experienced a major affective episode during the past year. However, 17 of their 24 borderline patients had lifetime mood disorders (e.g., dysthymia, cyclothymia, and atypical bipolar), and it was primarily these patients for whom the positive findings for the biological markers of a mood disorder were obtained. The results could then be interpreted to support either hypothesis, suggesting either that borderline personality disorder is associated with mood disorder or that the internal validity of the study was compromised by comorbid mood disorder in the subjects. The difficulty in differentiating borderline personality disorder from an Axis I disorder is compounded when more than two disorders are involved. Pope and Hudson (1989), for example, suggested that the substantial comorbidity of borderline personality disorder and bulimia reported in a number of stud-

ies has been an artifact of the overlapping constructs and diagnostic criteria sets. In the study by Levin and Hyler (1986), for example, bulimic subjects automatically satisfied two of the borderline personality disorder diagnostic criteria as a result of their binge eating (impulsivity) and the depression that follows a binge (affective instability). When Pope and Hudson excluded depressed mood and bulimic symptomatology from the diagnosis of borderline personality disorder, they found no comorbidity. However, the extent to which a diagnosis of borderline personality disorder ought not to involve mood is questionable (Kroll & Ogata, 1987). Many of the defining features of borderline personality disorder directly or indirectly involve affective dysregulation, including affective instability, physically selfdamaging acts, chronic feelings of emptiness, and intense relationships. Borderline personality disorder may represent a characterologic variant of mood (and impulse) pathology in the same manner that schizotypal personality disorder is a characterologic variant of schizophrenic pathology (McGlashan, 1987; Siever & Davis, 1990; Widiger, 1989). The same type of data for family history, biological markers, and treatment that supported the construct validity of schizotypal personality disorder by indicating its association with schizophrenia (e.g, Gunderson & Siever, 1985) could then be interpreted as supporting the construct validity of the borderline personality disorder diagnoses by indicating its association with depression. The latter research, however, is currently interpreted as questioning the validity of borderline personality disorder, consistently with the assumption that a disorder of personality ought to be distinct from a disorder of mood (eg., Gunderson & Elliott, 1985). The differentiation of a borderline personality disorder from depressive mood disorder parallels to some extent the distinction between personality traits and emotional states. This distinction is equally controversial (Fridhandler, 1986). Neuroticism, for example, is a fundamental dimension of personality that includes facets of trait depression and trait anxiety (Digman, 1990). Neuroticism involves the disposition to experience negative affective states (McCrae, 1983), and a correlation with mood states supports rather than questions its validity (Watson & Clark, 1984). Lenzenweger and Loranger (1989) made a similar point with respect to their finding that a measure of schizotypy included variance associated with anxiety as well as perceptual and body-image distortion. Rather than interpret this variance as reflecting artifactual state variance, they argued that the anxiety was consistent with the construct of schizotypy. Traits and states are perhaps best conceptualized as prototypal categories that provide a meaningful distinction but lack distinct boundaries (Chaplin, John, & Goldberg, 1988). Prototypic cases are readily differentiated, but the distinction becomes arbitrary at the boundaries. Some cases can be equally classified as states or as traits (Chaplin et al., 1988). Borderline personality disorder may represent a comparable instance of a mental disorder diagnosis that is literally on the boundary of the personality and mood disorders and may then represent both a personality and a mood disorder (Widiger, 1989). Antisocial and Substance Use Disorders There is a substantial association between antisocial personality disorder and substance use disorders (Docherty et al.,

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AXIS I AND AXIS II DISORDERS 1986; Tarter, 1988). However, the internal validity of this research is again compromised by the questionable independence of the diagnoses (Gerstley, Alterman, McLellan, & Woody, 1990; Nathan, 1988; see also Hare, Hart, & Harpur, 1991). The DSM-III-R diagnosis of antisocial personality disorder includes (but is not limited to) an inability to sustain consistent work behavior, failure to conform to social norms with respect to lawful behavior, failure to honor financial obligations, failure to plan ahead, recklessness in regard to safety, and inability to function as a responsible parent (American Psychiatric Association, 1987). The diagnosis of substance dependence includes hazardous behavior, theft, and the failure to fulfill major role obligations at home, school, or work. It is apparent that antisocial personality disorder and substance dependence behaviors are interdependent. Some of them are essentially equivalent, and it is not clear at times which (if any) direction of causality has occurred when one assesses the covariation of the presence of at least 4 of any of the 10 adult antisocial behaviors (the threshold for a diagnosis of antisocial personality disorder) with at least 3 of any of the 9 substance dependence behaviors, even with the requirement of the childhood antisocial criterion (Gerstley et al, 1990). One may be observing the co-occurrence of two disorders or simply giving one disorder two diagnoses (Frances, Widiger, & Fyer, 1990; Nathan, 1988). The problem is comparable to having overlapping self-report inventory scales. For example, the .79 correlation between the Millon Clinical Multiaxial Inventory (2nd ed.; MCMI-H; MilIon, 1987) antisocial personality disorder and drug dependence scales is impelled in part by sharing 50% of their items. Wiggins (1982) suggested that the MCMI-H ought not to be used to test theories about the relation between the respective disorders because the findings of any study will be biased by the item overlap. The same may be said for the overlap of the DSM-III-R diagnostic criteria for antisocial personality disorder and substance dependence (Gerstley et al, 1990).

Avoidant and Social Phobia Avoidant personality disorder and social phobia were new additions to the DSM-1II. DSM-III social phobia involves a "persistent, irrational fear of, and compelling desire to avoid, situations in which the individual may be exposed to scrutiny by others. There is also fear that the individual may behave in a manner that will be humiliating or embarrassing" (American Psychiatric Association, 1980, p. 227). DSM-III avoidant personality disorder involves a "hypersensitivity to potential rejection, humiliation or shame" (American Psychiatric Association, 1980, p. 323), an unwillingness to enter into relationships unless ensured of being liked, social withdrawal, and low selfesteem. Avoidant personality disorder and social phobia cannot be distinguished by course because social phobia is also said to be chronic, with an onset in late childhood or early adolescence. The major distinction is that in social phobia "a specific situation, such as public speaking, is avoided rather than personal relationships" (American Psychiatric Association, 1980, p. 324). However, various studies have suggested that the anxiety and avoidant behavior of social phobics is more pervasive than indicated by DSM-III (Liebowitz, Gorman,

Fyer, & Klein, 1985; Stravynski, Lamontagne, & Lavalle, 1986; Turner, Beidel, Dancu, & Keys, 1986). Liebowitz et al, for example, reported that 5 of their 11 social phobics "avoided almost all social interaction outside their immediate family" (p. 730). Avoidant personality disorder and social phobia may not in fact be distinct clinical entities but rather overlapping variants along a common spectrum of pathology (Brooks, Baltazar, & Munjack, 1989). Their co-occurrence may not involve the presence of two disorders but rather one disorder with two diagnoses. Interpreting the effect of their co-occurrence can be problematic. Reich, Noyes, and Yates (1989), for example, reported that avoidant personality disorder subjects with social phobia responded to an 8-week treatment with alprazolam and concluded that "alprazolam was able to significantly reduce many symptoms of avoidant personality disorder" (p. 94). Some might argue, however, that their findings could also suggest that the avoidant personality disorder traits were simply associated features of the anxiety disorder. The conclusion of Reich et al. (1989) is in fact somewhat ironic, given that Reich, Noyes, Coryell, and O'Gorman (1986) concluded on the basis of the same change scores on self-report measures of personality obtained from the same pool of subjects "that state anxiety. . .is a possible confounding factor in personality measurement" (p. 760). The change in personality disorder traits associated with alprazolam treatment was interpreted in one instance as a change in personality (Reich et al., 1989) but in another as an artifactual state effect of an anxiety disorder (Reich et al, 1986). The DSM-III-R did not facilitate their differentiation but rather increased their confusion. DSM-III-R now includes a generalized subtype of social phobia in which the fears "involve most social situations, such as general fears of saying foolish things" (American Psychiatric Association, 1987, p. 241), and avoidant personality disorder was revised to coincide more closely with the construct of a phobic character (Widiger, Frances, Spitzer, & Williams, 1988), which involves "a pervasive pattern of social discomfort, fear of negative evaluation, and timidity" (American Psychiatric Association, 1987, p. 351). The criteria for avoidant personality disorder include being "reticent in social situations because of a fear of saying something inappropriate or foolish" (American Psychiatric Association, 1987, p. 353). Turner and Beidel (1989) suggested that it is difficult to imagine a case of avoidant personality disorder that does not involve generalized social phobia. Social phobia is noted in the DSM-III-R as being a potential complication of avoidant personality disorder, but it is not really clear if social phobia is a complication or a manifestation (i.e, associated feature) of avoidant personality disorder (or vice versa). The co-occurrence of avoidant personality disorder with social phobia may then be as meaningless as a co-occurrence of schizotypal personality disorder with schizophrenia.

Options and Proposals A number of approaches are being considered for the DSMIV\o address the differentiation of personality and Axis I disorders. We discuss in particular adding exclusion criteria, shifting the placement of disorders, deleting overlapping criteria,

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adding differentiating criteria, and converting to a dimensional format.

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Adding Exclusion Criteria One approach to differentiation is to exclude the diagnosis of one disorder in the presence of the other. For example, in the DSM-III, social phobia could not be diagnosed in the context of avoidant personality disorder nor schizotypal personality disorder in the context of schizophrenia (American Psychiatric Association, 1980). However, many of the DSM-III exclusionary rules are now recognized as being rather arbitrary and artifactual (First, Spitzer, & Williams, 1990). They are useful in denning homogeneous groups for research purposes, but the homogeneity is at times by flat and does not accurately represent the actual heterogeneity within patient populations. Some are not particularly controversial (e.g., the exclusion of bipolar mood disorder in the diagnosis of antisocial personality disorder), but others force distinctions where perhaps none really exists. Many of the exclusionary rules were therefore deleted in DSM-I1I-R, including the prohibition against diagnosing social phobia in the context of avoidant personality disorder (American Psychiatric Association, 1987). The exclusionary rules can also be problematic in research. Eliminating borderline personality disorder subjects with major depression to control for mood is perhaps analogous to controlling for intelligence by eliminating the mentally retarded. The control is inadequate because a substantial amount of variance due to affective dysregulation still remains (e.g., Akiskal et al, 1985). McGlashan (1987), for example, was critical of the arbitrary DSM-III thresholds for determining the absence of a disorder. He indicated that many of his unipolar subjects without borderline personality disorder did in fact have borderline pathology, but because they were below the threshold for the borderline personality disorder diagnosis (i.e., had fewer than five features), they are classified as not having borderline personality disorder psychopathology. He concluded that "DSM-III emerges as poorly constructed for the study of comorbidity" (p. 473), given that the threshold for diagnosis does not actually exclude the presence of the pathology. A more adequate control for mood would be a covariate that assesses a full range of affective pathology. However, given that affective instability is part of the construct of borderline personality disorder, much of the variance that would be extracted from borderline personality disorder would not be artifactual. Extracting variance that is associated with mood pathology from borderline personality disorder would be analogous to extracting variance from schizotypal personality disorder that is associated with schizophrenic pathology (e.g., cognitive and perceptual aberrations). Shifting the Placement of Disorders Another approach has been to shift the placement of disorders. For example, the DSM-II diagnosis of cyclothymic (affective) personality was changed to a mood disorder of cyclothymia in DSM-III, and DSM-II latent schizophrenia became DSM-III schizotypal personality disorder. These revisions were to some extent inconsistent, and it has been suggested that

schizotypal personality disorder ought to be moved back to Axis I (Frances, 1980; Klerman, 1990; Rutter, 1987). As we indicated earlier, this move would also be congruent with the historical literature, the research that indicates an association of schizotypal personality disorder with schizophrenia (Gunderson & Siever, 1985), and the ICD-10. However, the placement of schizotypal personality disorder with schizophrenia may also undermine its validity as a personality disorder construct, reformulating it as a mild, subpsychotic variant of chronic schizophrenia, comparable with the DSM-III reformulation of the depressive and cyclothymic personality disorders as chronic, mild variants of a mood disorder. The DSM-III received substantial criticism for the failure to include a diagnosis that represented the construct of a depressive personality, opting instead for dysthymia on Axis I (e.g, Frances, 1980; Kernberg, 1984). Dysthymia is not distinguished from a personality disorder on the basis of age of onset or course because "it usually begins in childhood, adolescence, or early adult life" (American Psychiatric Association, 1987, p. 231) and it is usually chronic, in which case "the mood disturbance cannot be distinguished from the person's (usual) functioning" (American Psychiatric Association, 1987, p. 231). The confusion of Axes I and II has increased in DSM-III-R with the introduction of the early onset subtype of dysthymia that may be indistinguishable from the construct of a characterologic depression (Akiskal, Cassano, & Perugi, 1990; Klein, Taylor, Dickstein, & Harding, 1988). Keller, a member of the DSM-IV Mood Disorders Work Group, acknowledged that "early onset dysthymia corresponds to characterological depression or depressive personality, which emphasizes the temperamental traits of dysphoria, the tendency toward despair, and depressive personality traits as opposed to depressive states" (Keller, 1989, p. 158). A depressive personality disorder diagnosis has been proposed for DSM-IV (Phillips, Gunderson, Hirschfeld, & Smith, 1990), but a requirement for its inclusion is the ability to differentiate it from dysthymia. This may be as realistic as constructing a variant of latent schizophrenia that could be differentiated from schizotypal personality disorder. A variation on shifting the placement would be to move some of the personality disorders to Axis I but to retain each's label as a personality disorder (or code them on both Axes I and II). This acknowledges that the Axes I and II boundary is fluid, at times with no real distinction. This proposal, however, will resolve the problem only if the current boundary diagnoses, such as avoidant personality disorder and generalized social phobia, or early onset dysthymia and depressive personality, are collapsed into one diagnosis with common criteria. Otherwise, one is still left with the original problem of interpreting the comorbidity of overlapping constructs. It was in fact suggested in the development of DSM-III-R that the schizotypal personality disorder criteria set be equivalent to the prodromal or residual phases of schizophrenia (Widiger et al, 1988). The addition of odd or eccentric behavior and appearance to the schizotypal personality disorder criteria set reflected this sentiment. The conclusion that the respective Axes I and II disorders are equivalent and indistinguishable (at least at the boundaries) may not, however, represent a consensus position and there will likely be considerable disagreement with regard to which diagnoses ought to be collapsed and to what extent.

AXIS I AND AXIS II DISORDERS

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Deleting Overlapping Criteria A third approach is to delete overlapping criteria. Pope and Hudson (1989), for example, recommend deleting binge eating and depression from the diagnosis of borderline personality disorder, particularly when assessing the comorbidity of borderline personality disorder and bulimia. Some of the DSM-III criteria for the personality disorders were deleted in DSM-IIIR because they were present in more than one criteria set and it was presumed that they were contributing to excessive personality disorder comorbidity (Widiger et al, 1988). This approach, however, can artifactually decrease comorbidity by deleting the very features that two disorders have most in common. In addition, the deletion may substantially alter the validity of the measurement of the construct. Millon (1987) responded to the criticism of using overlapping scales in the MCMI-II by arguing that if the constructs do in fact overlap then the respective scales that assess the constructs must also overlap. It may inflate the estimate of the comorbidity of antisocial personality disorder and substance dependence to use MCMI-II scales that share 50% of their items, but an MCMI-II antisocial personality disorder scale without these items may not provide a valid measurement of the disorder. The same concern applies to diagnostic criteria sets. For example, the avoidant and schizoid personality disorders share the feature of social isolation. The presence of this overlapping criterion may inflate their comorbidity, but one can hardly provide a valid diagnosis of avoidant personality disorder without considering social isolation. The deletion of bulimic and affective symptomatology from the diagnosis of borderline personality disorder may be equally distorting. Pope and Hudson (1989) found substantially less comorbidity when they controlled for bulimic and depressive symptomatology, but one may also question whether they had in fact eliminated valid cases of borderline personality disorder. A variant of this approach is to replace the overlapping behavioral criteria with trait constructs. Gerstley et al. (1990), for example, suggested replacing the DSM-III-R antisocial personality disorder criteria with trait constructs of psychopathy (eg, egocentricity and lack of empathy) that do not explicitly include substance abuse criteria. However, this only hides the problem to the extent that the assessment of psychopathy trait constructs, such as impulsivity and poor behavioral control, continues to be based on substance abuse symptomatology and related acts. Another variant of this approach is to assess comorbidity with respect to individual items or features of disorders rather than the diagnoses (Akiskal et al, 1985). It may be easier to interpret the comorbidity of mood disorder with fears of abandonment or identity disturbance than with borderline personality disorder, which includes affective instability in the diagnosis. Likewise, the covariation of theft (from substance abuse) with the failure to conform to social norms (from antisocial personality disorder) may be tautological, but the covariation of theft with the failure to function as a responsible parent is not. Adding Differentiating

Criteria

The fourth approach is to add criteria that facilitate the differentiation of the two disorders. Gunderson and Elliott (1985),

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for example, suggested that borderline personality disorder and mood disorders can be differentiated on the basis of the quality or nature of the depressed mood. Borderline depression is said to be characterized by feelings of inner badness, self-condemnation, emptiness, and loneliness, whereas "affective depression" is characterized by feelings of guilt, sense of failure, and low self-esteem. Frances (1980) suggested that depressive personality can be distinguished from dysthymia by the absence of vegetative symptoms. The DSAf-/Kdepressive personality disorder proposal emphasizes cognitive symptomatology to facilitate its differentiation from dysthymia (Hirschfeld & Shea, 1990). A limitation of this approach, however, is that it presumes that a distinction ought to be made. It is in this respect complementary to the proposal to collapse the criteria sets. Both proposals beg the question. To the extent that the distinction is illusory, differentiating criteria will make artifactual distinctions. For example, it is not at all clear why a depressive personality disorder should not include somatic signs of mood pathology. These signs may represent biological markers for the personality disorder, comparable with the biological markers for schizotypal personality disorder. Emphasizing cognitive features over behavioral, motivational, affective, and interpersonal ones is also contrary to the pervasiveness that is fundamental to the construct of a personality disorder (Millon, 1986). A variant of this approach is to replace the polythetic format of diagnosis that provides multiple, optional criteria with a requirement of a single, core criterion that would be specific to each disorder (Widiger & Frances, 1985). This proposal has been particularly appealing to address the overlap among the personality disorders. For example, the problematic overlap of the avoidant and dependent personality disorders may be resolved by requiring the presence of social isolation in the diagnosis of avoidant personality disorder, given that social isolation is rare in most cases of dependency. However, a limitation of this approach is determining the core feature of each personality and Axis I disorder. It is unlikely, for example, that there will be much agreement with regard to the core feature of the schizotypal or borderline personality disorders. In addition, to be effective in differential diagnosis, a core feature must be pathognomonic (i.e, maximally sensitive and specific), and there are few mental disorders that have a pathognomonic criterion (e.g., social isolation differentiates the avoidant from the dependent but not the avoidant from the schizoid). Another variation of this approach is to give more emphasis to the defining features of a personality disorder, such as chronicity and pervasiveness. A DSM~III-R personality disorder is pervasive, begins by early adulthood, and is present in a variety of contexts (American Psychiatric Association, 1987), but no guidelines are provided to ensure that the observed symptomatology is in fact pervasive, chronic, or present in a variety of contexts. It will be helpful if the diagnostic criteria specify how the personality disorder manifests itself across situations (e.g., work, leisure, and social activities) and periods of life (e.g, adolescence, early adulthood, middle age, and older age) and provide a minimal duration of time. Millon (1986) suggested that the criteria sets explicitly represent each of the major domains of personality functioning (e.g, cognition, affect, interpersonal relations, and behavior). Some

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personality disorders may be more evident in one area than another (e.g., schizotypal personality disorder in the cognitive realm and dependent in the interpersonal), but if it is not readily apparent that the full domain is involved and the manifestation within each domain cannot be described, then it may be difficult to argue that it is in fact a disorder of personality. On the other hand, some personality traits may be confined largely to one domain of functioning (e.g., cognitive, interpersonal, or mood), and when these traits are maladaptive, they can be said to constitute a disorder of personality functioning.

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Converting to a Dimensional Format All of the foregoing options maintain the categorical format for diagnosis. The proposal to place diagnoses on both Axes I and II acknowledges that no real or nonarbitrary distinction can be made, but this option still retains the categorical diagnoses. A fifth option is to convert to a dimensional format. There are a number of advantages to the dimensional approach. Categorical distinctions provide clear and vivid characterizations and are consistent with medical tradition, but to the extent that the distinctions are arbitrary, they contribute to a variety of classificatory dilemmas and misleading stereotypes (Cantor & Genero, 1986; Schacht, 1985; Widiger & Frances, 1985). The DSM-III-R converted the diagnoses for disruptive behavior, psychoactive substance use, and personality disorder from a monothetic to a polythetic format in recognition of the substantial heterogeneity among the members of the diagnostic categories with respect to the disorders' symptomatology (Spitzer, 1987). A dimensional format can go further by indicating the degree to which the symptomatology is present and providing thereby a more precise description of the individual patient. The dimensional format also retains the flexibility of allowing the use of alternative cutoff points for various clinical decisions (e.g., Finn, 1982). A dimensional classification has particular relevance to the personality disorders, as personality classification within psychology has usually involved a dimensional model (Widiger & Frances, 1985). The five-factor model appears to be a particularly compelling alternative to the DSM-I11-R categorical diagnoses (Costa & McCrae, 1986; Digman, 1990; Widiger & Trull, in press; Wiggins & Pincus, 1989). One of the dimensions from the five-factor model is neuroticism, which includes facets of anxiety and depression that would likely be indistinguishable from generalized social phobia and early onset dysthymia (Zonderman, Herbst, Schmidt, Costa, & McCrae, 1990). Dimensional models for anxiety and depression have also been developed (e.g., Watson, Clark, & Carey, 1988), and it is no coincidence that the mood dispositional dimension of negative affectivity is essentially equivalent to the personality dimension of neuroticism (Costa & McCrae, 1985; Watson & Clark, 1984). A conversion to a dimensional approach, however, will represent a major revision to the nomenclature, and various concerns have been raised (Frances, 1990). Many clinicians, for example, are likely to be unfamiliar with such dimensions as positive affectivity and agreeableness and may have difficulty applying them to their clinical practice. The dimensional models emphasize the classification of normal personality and mood dispositions, whereas the diagnostic manual concerns

the classification of disordered functioning. There is, in addition, a lack of consensus in regard to which dimensions of personality, anxiety, and mood ought to be emphasized. Finally, it is not yet clear how a dimension of negative affectivity or neuroticism would affect the anxiety and mood disorders that are not currently on the boundary with personality disorders. Nevertheless, the advantages of a dimensional approach may justify at least some formal acknowledgment of this alternative perspective, particularly if many of these problems can be addressed (Widiger, 1990). Conclusions The distinction between Axes I and II disorders is useful and usually valid. However, the reification of these constructs through diagnostic criteria sets that demarcate categorically distinct entities is at times problematic and perhaps even illusory. Prototypic cases of antisocial, avoidant, schizotypal, and borderline personality disorders are clearly distinct from prototypic cases of substance abuse, social phobia, schizophrenic, and mood disorder (respectively). Typical cases, however, are not prototypic, and many actual cases are literally borderline. It is our recommendation that future research address the fundamental taxonomic question of whether the Axes I and II constructs do in fact involve distinct entities or whether they are simply useful distinctions that have been imposed along various spectra of pathology. Many statistical techniques and the data they produce can be brought to bear on this question; such techniques include the relative concurrent and predictive validity of the dimensional and categorical models, the invariance of factor analytic solutions across categorical distinctions, admixture analysis, and maximum covariation analysis. A review of these approaches is beyond the scope of this article, but detailed discussions are provided elsewhere (Golden, in press; Grove & Andreasen, 1989; Miller & Thayer, 1989; Trull, Widiger, & Guthrie, 1990). These approaches will not provide unambiguous results, but it may not be possible to decide which proposals to adopt until it is clear whether any categorical distinctions are in fact valid. References Akiskal, H. S., Cassano, G. B., & Perugi, G. (1990, May). The significance of the depressive temperament. In R. M. Hirschfeld (Chair), Depressive personality disorder: Current status. Symposium conducted at the 143rd annual meeting of the American Psychiatric Association, New York. Akiskal, H. J., Yerevanian, B. I, Davis, G. C, King, D, & Lemmi, H. (1985). The nosologic status of borderline personality; Clinical and polysomnographic study. American Journal of Psychiatry, 142.192198. American Psychiatric Association. (1968). Diagnostic and statistical manual of mental disorders (2nd ed.). Washington, DC: Author. American Psychiatric Association. (1980). Diagnostic and statistical manual of mental disorders (3rd ed.). Washington, DC: Author. American Psychiatric Association. (1987). Diagnostic and statistical manual of mental disorders. (Rev. 3rd ed.). Washington, DC: Author. Brooks, R. B., Baltazar, P.L..& Munjack, D. J. (1989). Co-occurrence of personality disorders with panic disorder, social phobia, and generalized anxiety disorder: A review of the literature. Journal of Anxiety Disorders, 3, 259-285.

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