Classification &
Research
The study of mental disorder
involves:
Definition: What do we mean by
mental disorder?
 Classification: How do we distinguish
between different mental disorders?
 Explanation: How do we understand
mental disorder?
 Treatment: How do we treat mental
disorder?

Example

Animal
Dog
 Cat

• LINNAEAN CLASSIFICATION
• Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Mammalia
Subclass: Theria
Infraclass: Eutheria
Order: Primates
Suborder: Anthropoidea
Superfamily: Hominoidea
Family: Hominidae
Genus: Homo
Species: sapiens
Why is it important to
classify mental disorders?
Scientific communication and
research
 Treatment

Classification and Diagnosis
Classification systems exists before
and independently any individual
 Individual people are said to be
diagnosed or put into the
classification system based on a
psychological assessment

Evaluating classification
systems and assessment
tools?

Reliability: Gives the same answer with
repeated measurement or assessment
Test re-test
 Inter-rater or inter-judge

Evaluating classification
systems and assessment
tools?

Validity: Measures or assesses what it
claims to measure
Descriptive, construct
 Predictive

Three broad ways to classify
mental disorder
Categorical Approach
 Dimensional Approach
 Prototypal Approach

Categorical Approach
Characteristic of medical diagnostic
systems.
 Assumptions:

Behavior can be divided into categories
of “healthy” and “disordered”.
 There are discreet, non-overlapping
types of “disorder”
 Members of each diagnostic group share
the same features.

Dimensional Approach
Characteristic of personality assessment
approaches.
 Assumptions:

Behavior comes from different
strengths/intensities of underlying
attributes (e.g., aggressiveness,
introversion).
 People differ along a continuum of
normality to abnormality on these
dimensions.

Prototypal Approach
There are imperfect but recognizable
combinations of characteristics that
cluster together.
 These imperfect clusters define
abnormal behavior.
 Assumptions:

No people share all of the features of the
prototype.
 All people share most of the features of
the prototype.


Defines what is abnormal
Classifies mental disorders into different subtypes and provides defining criteria

Medical tradition:



Categorical in intention
Prototypal in practice
DSM-IV
Created with assumptions of the
categorical approach
 BUT…

Central features of Dx categories are
sometimes unclear.
 Many shared features between Dx
categories.
 Large amount of co-morbidity.

DSM-IV
DSM-IV classification is prototypal
because...
Fuzzy boundaries between
categories.
 Overlap of categories themselves.

DSM-IV: A short history
DSM = Diagnostic and Statistical
Manual (of mental disorders)
 Currently in 4th edition (May, 1994).

DSM I and II:
 Included a lot of jargon.
 Narrative categories.
 Categories not well defined.
 Generally not reliable.
DSM III (1980):
 Radically new approach...
DSM-III
Precise definitions of Dx categories.
 Necessary requirements to meet Dx
category.
 First attempts to establish reliability
and validity for Dx categories.

DSM-IV
Latest edition (1994)
 Five Axis structure:
Axis I - Clinical Syndromes
Axis II - Personality Disorders
Axis III - Related Medical Conditions
Axis IV - Psychosocial and Environmental
Problems
Axis V - Global Assessment of
Functioning.

DSM-IV criticisms:
1. Long-term outcome of disorders is
largely unknown.
2. Still little known about etiology.
3. High co-morbidity among Dx.
4. Reliability emphasized at expense of
validity (?)
DSM-IV criticisms cont.
5. Perpetuation of flawed Dx categories
(from past DSMs).
6. Too many dimensions require rating.
Classification
Problems

Labeling

Pseudo-explanations

Lack of reliability
Classification
Advantages:
Communication shorthand
 Treatment planning
 Etiology
 Aid to scientific investigation

Further Exploration:
Classification
Millon, T. (1991). Classification in
Psychopathology: Rationale,
Alternatives, and Standards. Journal
of Abnormal Psychology, 100(3), 245261.
 Krueger, R., Piasecki, T., M. (2002).
Toward a dimensional and
psychometrically-informed approach
to conceptualizing psychopathology.
Behaviour Research and Therapy, 40,
485-499.

Research Methods and
Critical Thinking
Observation

Like all sciences the “bedrock” is
observation/description
Observation as theory free or theory
laden
 Description determines what we can
then later say about a phenomenon
 Reliability and Validity

Hypotheses & Predictions

Hypothesis: A claim about
observations/descriptions that could
be true or false that attempts to
explain or understand the world


Tested by making predictions
Prediction: also important from a
clinical point of view, not just to test
hypotheses

Can predict without understanding
Understanding

Understanding: Usually means “what
causes X” could also mean “what is it
like, or what does it mean to a person
to have X”
Causality:
Requirements for inferring causality:
1) Covariation - purported cause and
observed effect vary together.
2) Temporal Precedence - purported
cause occurs before the observed
effect.
3) Exclusivity - the purported cause is
the only thing that can explain the
observed effect.

Correlation / Covariation vs.
Causation

Hypothesis: Stress causes depression

Need to show that depressed people
(Criterion Group) had higher stress
levels, before becoming depressed,
than other people who do not become
depressed (Control Group).
Control / Intervention

Without understanding it is hard to
control or intervene
Research Designs
Intensive observation of a single case
 Observation of groups

Internal and External Validity

Internal validity


The study can make accurate
conclusions because there are no
confounds or alternative explanations
External validity

The results can be generalized to
people outside the study
Sampling and
Generalization
Population: Everyone who has the
mental disorder that you want to make
claims about
 Sample: A smaller group of people
from the lager population of interest
 Random Sampling: Everyone in the
population has an equal chance of
being in the sample

Sampling and
Generalization

If the sample is not random, or not a
good mix of all the people that have
the mental disorder then the
conclusions may not have external
validity or may not generalize
Methods of Control
Manipulating or systematically
changing one variable while
controlling or holding constant other
variables
 Allows us to conclude that any
observed effects of changing a
variable are really due to it and not
other variable
