Competing Classifications

The indistinctness of psychiatric syndromes and of the rules for deciding whether individual disorders meet symptomatic criteria has major implications for attempts to operationalize psychiatric classifications. There are currently two systems that have wide acceptance, the Diagnostic and Statistical Manual (DSM) of the American Psychiatric Association (APA) and the World Health Organization (WHO)'s International Classification of Disease (ICD). In the early days, revision of classificatory schemata relied almost wholly on clinical reflection. However, since the classifications are set up primarily for scientific purposes, they should properly be modified in the light of empirical research that permits definitive statements about their utility. The standardized and operationalized classifications that are now in existence offer an opportunity for using research in this way.

Unfortunately, much of the pressure for change has continued to originate from clinical and political demands. Revisions have sometimes had the appearance of tinkering in order to capture some imagined essence of the disorders included (Birley, 1990). What looks like fine-tuning can nevertheless make considerable differences to whether individual cases meet criteria or not, and thus disproportionately affects the putative frequency of disorders. We should jettison classifications only on grounds of inadequate scientific utility and as seldom as possible, since too rapid revision defeats the objective of comparison. Like all such classifications, DSM and ICD are created by committees. The natural tendency to horse-trading between experts selected precisely because they are powerful and opinionated leads to an over-elaborate structure, an excess of allowable classes and subclasses, and complicated defining criteria. Thus, in DSM-IV-R (APA, 1994), there are potentially 14 categories to which depressed mood can be allocated, and in ICD-10 (WHO, 1992) there are 22. Greater utility would probably accrue from limiting the primary categories to three (bipolar disorder, unipolar depressive psychosis, and unipolar non-psychotic depression), and epidemiological research often uses these categories in any case. In Table 1.1, I have provided a comparison of the definitions of depressive disorder under DSM-IV (APA, 1994) and ICD-10 (WHO, 1992), slightly simplified. Over the years, there has been considerable convergence between the systems. However, the differences remain important. The categories are too close together for empirical studies to establish their relative validity, but far enough apart to cause discrepancies in identification. Relatively severe cases are likely to be classified as depressive disorder under both systems. However, milder disorders may be cases under one system, and not the other. This becomes important in epidemiological studies of depressive disorder in the general population because such studies usually report their results under one system or the other, and the degree of comparability is hard to quantify. Thus, the use of different classificatory systems is one barrier to comparison between studies: there are others.

It is of interest to see the effect of applying algorithms for the diagnostic categories defined by different systems to a common set of symptom data. The Schedules for Clinical Assessment in Neuropsychiatry (SCAN) (WHO, 1992) allows diagnosis under both DSM and ICD. In Table 1.2, I have illustrated the effect of applying ICD-10 and DSM-IV criteria to the data from the Derry Survey (McConnell et al., 2002) on the identification of cases of depressive episode (ICD) and depressive disorder (DSM). Of the 18 participants diagnosed as having a depressive condition by one classification, two-thirds were diagnosed by both. Five cases of depressive episode were not diagnosed as DSM depressive disorder, whereas only one case of depressive disorder was not diagnosed as ICD depressive episode. In contrast, DSM recognized many more cases of anxiety disorder. Fifteen of the cases

Table 1.1 Criteria for depressive episode

DSM-III-R/DSM-IV

ICD-10

Symptoms present nearly every day in same 2-week period

Change from normal functioning

Depressed mood Anhedonia

Ancillary symptoms (n = 7)

Fatigue/loss of energy Weight/appetite loss/gain Insomnia/hypersomnia Observed agitation/retardation Low self-esteem/guilt Impaired thinking/concentration Suicidal thoughts

Criteria: one key, five symptoms in total Plus

Significant distress Or

Social impairment

Exclusions

Not mixed episode Not substance related Not organic Not bereavement Not psychotic

Episode must have lasted at least 2 weeks with symptoms nearly every day

Change from normal functioning

Depressed mood Anhedonia

Fatigue/loss of energy

Ancillary symptoms (n = 7)

Weight and appetite change Sleep disturbance Subjective or objective Agitation/retardation Low self-esteem/confidence Self reproach/guilt Impaired thinking/concentration Suicidal thoughts

Criteria:

Mild episode: two key, four symptoms in total Moderate: two key, six symptoms in total Severe: three key, eight symptoms in total

Exclusions

No history (ever) of manic symptoms Not substance related Not organic

Table 1.2 DSM-

-R and ICD-10 classification based on the same symptom data. The Derry Survey (McConnell et al., 2002)

No depressive diagnosis Depressive episode ICD-10 Kappa =

No anxiety diagnosis Anxiety disorder ICD

Kappa

No depressive diagnosis Depressive disorder DSM

No anxiety diagnosis

0.68

Anxiety disorder DSM

defined by DSM were not classed as anxiety disorders by ICD, while only two classified by ICD were not so classed by DSM. Thus, the ICD criteria appear to be less stringent for depressive episode, while the reverse is true of anxiety. The results suggest that the difference between the two systems arises because of differing thresholds rather than because of wide differences in the symptom contents of the classes.

Anxiety and Depression 101

Anxiety and Depression 101

Everything you ever wanted to know about. We have been discussing depression and anxiety and how different information that is out on the market only seems to target one particular cure for these two common conditions that seem to walk hand in hand.

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