The Diagnostic and Statistical Manual is
neither diagnostic nor statistical, but it is a godsend to any insurance-based
health system, because every patient must have a diagnostic number before they
can claim their money back, and every diagnosis requires a medicine, which
makes the manual attractive to pharmacological companies. The recent controversy
about the 5th revision is in some ways a compliment, because it shows
that it has established itself as a major reference work.
The problem is that the manual has
always been a muddle of conflicting opinions, often ill at ease with itself. It
is not based on a statistical approach to mental health problems arising from a
proper epidemiological population study, but rather to a committee-based
discussion about the common constellations of problems encountered by
psychiatrists in clinical practice. Because psychiatrists cannot always agree,
the manual follows a pick-and-mix approach to diagnosis, in which all you need
to have is 1 or 2 symptoms out of 4 or 5 in each category, such that patients
can attain the diagnosis with a very different pattern of symptoms. In line with American productivity, the list
has expanded generously from one edition to the next, (see Icebergs and Onions)
as if madness were increasing, a sort of Flynn Effect of lunacy.
It is not all rubbish, because psychiatrists
can notice patterns like any other professionals, but it tends to generate many
over-lapping descriptions, and a proliferation of categories, sometimes under
pressure from patient groups, who see the whole exercise as a matter of obtaining
legitimacy, whilst others campaign to have themselves removed from the list,
such as homosexuals who do not see that their sexual preferences constitute a
disorder.
Knowing that they would not be able to
agree on a common theory, the participant psychiatrists have ended up as
butterfly collectors exhibiting an assembly of brightly coloured disorders,
each with a proud catalogue number. One particularly gaudy specimen is “disorders
not otherwise specified”, a rather common Lepidoptera, it would seem.
How should a
psychiatric/psychological disorder be defined? Four tests provide a useful
start.
1 The diagnosis should have internal
coherence, with the relevant symptoms having positive predictive value one to
the other. Each symptom should be more strongly correlated with the other
symptoms in the diagnosis than they are usually correlated with other
extraneous problems. One positive symptom should predict the other positive
symptoms, such that they all occur together more frequently than in other disorders.
(In statistically terms, there must be
high correlations between most of the symptoms, such that you could get a high
R squared in a multiple regression equation).
2 The diagnosis should be distinct from
other groupings, with minimal overlap. Some aspects such as depression or
anxiety will be very common, but there must be something distinctive if the
disorder is to have a separate category name. (In statistical terms they should be distinct
using cluster analysis, or discriminant function analysis, all of which should
be apparent using old-fashioned t tests between the group symptom totals).
3 Ideally, there should be some
therapeutic or research advantage to the classification. In the absence of
clear biological indicators, diagnostic categories have to be provisional, but
they can often be clinically useful. (In
statistical terms the diagnoses must predict different outcomes and responses
to treatment, and reduce errors of prediction as regards outcomes).
4 It should not be an arbitrary sub-set which leads to tautological
self-confirmations. By cherry picking your cases you can create many apparent
syndromes. For example, by studying only those cases of autism in which the
parents believe that the condition was brought about by a vaccination, you can
quickly gather suggestive data implying that there is a syndrome of vaccine
damaged children with resultant autism. (In statistical terms the samples have
to be drawn randomly from the
population and the symptoms and putative causes must be considered objectively
for cases and non-cases).
Here is a list of generic problems with
DSM which I produced some years ago:
1. Neither diagnostic nor statistical, just a
stamp collection
2. No cluster analysis, so disorders are poorly
differentiated and poorly supported
3. Does not give statistics of symptom frequency
for each diagnosis
4. Categorical, not dimensional, which is
against the evidence.
5. Too many disorders, many of them overlapping
6. Diagnostic categories are over-inclusive and
pathologize ordinary life
7. Not purely scientific, but manipulated by
interest groups
We are now
awaiting the 5th edition of DSM. The British Psychological Society
has got its retaliation in first http://apps.bps.org.uk/_publicationfiles/consultation-responses/DSM-5%202012%20-%20BPS%20response.pdf
My own view is
that the proper way to look at psychological problems is to study the mental
health of entire populations. When you do that you usually find dimensions
rather than categories. Take depression. Most people have low mood sometimes.
Some people have low mood more frequently. A minority have episodes of extremely
low mood, and at those times are very vulnerable, and at risk of
self-harm. Psychologists (and quite a
number of psychiatrists) prefer the dimensional approach. They argue that there
are no common disorders, only extremes of quantitative traits.
However,
although the dimensional approach makes most sense most of the time, some
conditions may well represent a discontinuity. For example, all of us may feel
suspicious about how we are being treated from time to time (particularly within
large institutions) and this might seem no more than understandable mild paranoia.
Not every promotion is achieved by the best candidate. Suspicion is natural,
and sometimes justified. Yet the level of suspicion in severe paranoia is of a
different order of magnitude. It corrodes the sufferer’s ability to live a
productive life. Perhaps there is a real paradigm shift in such cases. The
category of paranoid schizophrenia may stand up as a category. It is very
different, and different from the shades of depression and anxiety which
commonly affect most people.
At a more basic
level, it would be good to have some theoretical basis for diagnosing mental
disorders. A diagnosis of schizophrenia usually is associated with a sharply
reduced level of contribution to society, and a fourfold increase in violence.
A diagnosis of anorexia nervosa is associated with increased mortality, with
about 10% of sufferers dying young. Depression and anxiety at the extreme levels
of the trait are very handicapping, and severe depression is associated with
suicide. Homosexuality is not currently a diagnosis, but it is associated with
sharply reduced fertility. Which, if any of these outcomes, makes us feel that
something has gone very wrong with the person in some important regard?
In the meantime, it is very likely that
your own personal problem has a number, and that the latest edition has been
written purely to classify you. The
tablets are in the post.
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