Utility of Categorising Mental Illness

Van Gogh Bandaged Ear

In a previous post I described
how current methods of categorising mental health problems are not particularly
reliable or valid. As Kendell and Jablensky (2003) point out, the lack of a
clear dividing line between different categories of mental illness is a serious
theoretical problem.
Nevertheless, the categories,
flawed as they are, do have practical utility. Indeed, the DSM-IV states that
no assumption should be made that there are entirely separate categories of
mental illness. Similarly it states no assumption should be made that there is
a clear dividing line between the sane and the insane. Despite these
disclaimers, what is the practical effect of categorisation?
The three most important uses
of a classification system are in aetiology, treatment and prognosis; or where
the illness has come from, what can be done about it and, what might happen to
you. Perhaps the most important of these for the patient is prognosis: “What
will happen to me?”.
Bentall points out the
difficulty of assessing the outcomes of people with a mental illness because
they are often variable across different domains. Clinical outcome attempt to
measure the persistence of symptoms, occupational outcomes measure the ability
to keep a steady job, while social outcomes measure a patient’s network of
Despite this, Bentall reports
3 general findings from the evidence on the outcomes of those diagnosed as

  • The course of psychosis is
    unpredictable. The only fairly solid finding is that the occurrence of psychotic
    episodes seem to increase the probability that they will occur again in the
    future. This process is known as kindling.
  • There is little predictive
    power for individual patients from a diagnosis. This conclusion comes from the
    evidence that there is enormous variability in the outcomes of people with the
    same diagnosis.
  • Patients with a diagnosis of
    manic depression have a better outcome, on average, than those with a diagnosis
    of schizophrenia. Despite this, evidence has shown there is no sharp delineation
    between the two diagnoses. Kendell & Brockington’s (1980) study showed the
    difference manifested itself in a sliding scale. The more a person’s symptoms
    were typical of schizophrenia rather than an affective disorder, the poorer was
    the outcome.
Moving away from the patient
and thinking of the utility of these categories for the academic, though, how
do the fuzzy categories affect research? At first sight, it seems that having a
number of categories of mental illness is a serious advantage in research.
Before the standardisation introduced in the 70s by categorisation, researchers
in different places used different definitions so it was difficult to compare
results and theories. Categories provide a common language – and that can
provide synergy through a common understanding.
The problem is, over time,
categories become embedded within the collective consciousness. It becomes
accepted, whether explicitly or implicitly, that research can only be conducted
with reference to, and with the use of, the official categories. This clearly
limits the possibilities for progress. Categories that have, theoretically,
been found wanting, persist simply because the effort required to change that
many minds is too great.
A related and more
sociological idea is the effect of categorisation on the individual. There is
an element by which once people receive a label, they then define themselves,
and are defined by others, in relation to that label. A person suffering from
manic depression becomes less a person than ‘a manic depressive’. If this
category is theoretically flawed, then what does this mean about how those
suffering mental illness are being defined by others and defining themselves?
More to come about aetiology
and treatment in further posts.
About the author

Psychologist, Jeremy Dean, PhD
is the founder and author of PsyBlog. He holds a doctorate in psychology from
University College London and two other advanced degrees in psychology.
He has been writing about
scientific research on PsyBlog since 2004. He is also the author of the book
“Making Habits, Breaking Habits” (Da Capo, 2003) and several ebooks.

Kayode Ojo
Kayode Emmanuel Ojo is the Co-Founder and Managing Director at SHEFFA Limited. He is presently studying Computer Science at the National Open University, Victoria Island, Lagos.