Transcript Classification and Diagnosis

Characteristics of A Useful
Diagnostic System
 Facilitates Communication
 Possesses Etiological Validity
 Provides Reliable Information on
Disabilities, Abilities, Functional
Impairments, etc.
 Guides Research (homogeneous groups)
 Informs Treatment Decisions
 Predicts Clinical Course
History of Psychiatric Diagnosis
 End of the 19th century - diversity of
classifications a major problem
 1939 - WHO adds mental disorders to
International list of Causes of Death (ICD)
 1948 - ICD covers abnormal behavior
 1952 - American Psychiatric Association
Publishes the DSM - I
 1969 - WHO publishes new classification
system. APA follows with DSM-II
History of Psychiatric Diagnosis
 1980 - APA publishes extensively revised
DSM-III, followed by a somewhat revised
DSM-IIIR.
 1994 - DSM-IV published - coordinated
with the development of ICD-10
 DSM-IV developed by committees - content
determined through consensus and voting
 Committees included both psychiatrists and
psychologists
Caveats Acknowledged by DSM-IV
“There is also no assumption that all
individuals described as having the same
mental disorder are alike in all important
ways. The clinician using DSM-IV should
therefore consider that individuals sharing a
diagnosis are likely to be heterogeneous
even in regard to the defining features of the
diagnosis and that boundary cases will be
difficult to diagnose in any but a
probabilistic fashion” (p. xxii)
Caveats Acknowledged by DSM-IV
 “The specific diagnostic criteria included in
DSM-IV are meant to serve as guidelines to
be informed by clinical judgement and are
not meant to be used in a cookbook fashion.”
(p. xxiii)
 “It is precisely because impairments,
abilities, and disabilities vary widely within
each diagnostic category that assignment of a
particular diagnosis does not imply a specific
level of impairment or disability.” (p. xxiii)
Caveats Acknowledged by DSM-IV
 “Nonclinical decision makers should also be
cautioned that a diagnosis does not carry any
necessary implication regarding the causes of
the individual’s mental disorder or its associated
impairments.” (p. xxiii)
 “Moreover, the fact that an individual’s
presentation meets the criteria for a DSM-IV
diagnosis does not carry any necessary
implication regarding the individual’s degree of
control over the behaviors that may be
associated with the disorder.” (p. xxiii)
DSM Growth in Pages
1000
900
886
800
P
A
G
E
S
700
600
567
500
494
400
300
200
100
128
0
I (1952)
134
II (1968) III (1980)
III-R
(1987)
IV (1994)
DSM Growth in Diagnostic Categories
20
19
18
18
15
Number of Major
Categories
11
10
8
5
I (1952)
II (1968)
III (1980)
DSM Edition
III-R (1987)
IV (1994)
DSM Growth in Labels
400
398
300
292
Number of
Diagnostic Labels
265
200
182
100 106
I (1952)
II (1968)
III (1980)
DSM Edition
III-R (1987)
IV (1994)
Multiaxial Classification
 Axis I - All categories except personality
disorders and mental retardation
 Axis II - Long-term disturbances
 Axis III - Medical conditions believed to be
relevant to the mental disorder in question
 Axis IV - Psychosocial and behavioral
problems which may contribute to the disorder
 Axis V - Current level of adaptive functioning
Criticisms of Psychiatric Diagnosis
 Categorization leads to loss of information
 Categorical vs. Dimensional Classification
 Diagnoses have negative effects on those
labeled
 Reliability of Diagnosis
 Validity of Diagnostic Categories
 Ignores Contextual and Cultural
Considerations
Sensitivity and Specificity
 Sensitivity - agreement regarding the
presence of a specific diagnosis
 Specificity - agreement concerning the
absence of a diagnosis
 The rate of false positives and false
negatives will depend respectively on the
sensitivity and specificity of the diagnostic
rules
Example of Kappa Computation
Clinician 1
Clinician 2
Diagnosis +
Diagnosis N
Diagnosis +
3(a)
3(b)
6
Diagnosis 3(c)
91(d)
94
Total N of Cases
6
94
100
_______________________________________________
Pc is computed from marginals (.94)2 + (.06)2 = .8872 on the
assumption that C1 and C2 have equal rates of false positives
and false negatives.
Po = a + d = (.03) + (.91) = .94
k = (.94) - (.8872) / 1 - (.8872) = .468
Effect of Base Rates
1.0
0.9
Sensitivity = 0.80, Specificity = 0.98
Kappa
0.8
0.7
0.6
K varies as a joint function
of “True” Base Rates,
Sensitivity, and Specificity
of the Diagnostic
Procedures.
0.5
0.4
Sensitivity = 0.40, Specificity = 0.98
0.3
0.2
0.1
0.0
.10
.20
.30
.40
.50
.60
.70
“True” Base Rate
.80
.90
1.00
Validity
 The extent to which accurate statements and
predictions can be made about a diagnostic
category.
 Etiological Validity - similar causal factors are
found among individuals in a diagnostic group.
 Concurrent Validity - other symptoms or
disordered processes not part of the diagnosis itself
are discovered to be characteristic of those
diagnosed.
 Predictive Validity -similar future behavior on part
of the disorder or patients suffering from it.