How mental health can claim to be a science, why mental healthcare can't claim to be a science and how this problem affects the diagnostic criteria

Without the rigour of the trials that make up DSM IV and ICD the mental
health system can not claim to be a health system nor can it claim to
treat illness. Perhaps even with the science it still doesn't make
things an illness.

The cluster of symptoms approach is based upon the application of early
positivist science techniques with modern analytical techniques to
define through epidemiological trials and other forms of data the course
or life path of people of a certain type. This is one of the reason it
psychiatry is compared to astrology. Evidence-based medicine demands
proof. The proof is the research.

Much of mental health research is very difficult. The hardest problem is
the small effect sizes compared to physical illnesses.

The operational cluster of symptoms approach was developed, perhaps, in
responses to the antipsychiatry movement of the 1970s. Szasz's erudite
and well reasoned arguments, studies like the Rosenthal experiment and
other challenges to the purported scientific basis for the 'treatment'
of mental 'illnesses' pushed the establishment to a more scientific
approach.

The replication of the results can only be achieved by replication of
the conditions in the study. At every deviation the results become less
valid.

Schizoaffective disorder is a controversial diagnosis in the psychiatric
profession. Many disagree with its existence. Others consider that it is
irrelevant and that it's all lumped together as one based on the
Kraeplinian biomedical model, i.e. there is no separation between
schizophrenia and bipolar.

It exists based on the same quality of evidence (though less) as bipolar
and schizophrenia and other mental disorders. Based on the idea of
prognosis and the link to the definition of mental illness
schizoaffective has been proven to be a different disorder based on
different occupational and social outcomes and sits somewhere between
bipolar and schizophrenia.

In practice many, many NHS psychiatrists don't stick to the diagnostic
criteria or the law, for better or for worse. Immediately upon moving
away from the strict research diagnostic criteria and other practices at
the same degree of rigour as the research studies a practioner looses
any right to call their practice a science. However this conformity to
rigidity in clinical practice would drive many psychiatrists insane.

The problem of clinicians lack of understanding of research and how it
fits together with the idea of science and evidence-based medicine is
why schizoaffective disorder may be removed from the American diagnostic
system and this will likely influence practice in the UK over the next
few years. The diagnosis exists in research but practicing psychiatrists
are incompetent to use it because they don't stick to the diagnostic
cluster of symptoms. There may be other more complex reasons why this
diagnosis is being left out of the revision of DSM.