Background. Studies from several countries have shown
a
decline, in the last few decades, of the
number of admissions with a diagnosis of schizophrenia. This could be due
to
a fall in the incidence
of schizophrenia, but it also could be due to confounding factors. The
hypothesis tested in the study is that the incidence of schizophrenia is
actually falling because of a decrease in the presence
of a seasonal aetiological agent.
Methods. The hypothesis was tested by analysing the dates of
birth of the patients discharged with
a diagnosis of schizophrenia from NHS hospitals in England and Wales and
would be confirmed
by an appropriate change in the seasonality of the births over time.
Results. Evidence of seasonality has been observed in the schizophrenic
births, but with no significant change over time.
Conclusions. The fall in first admissions with a diagnosis
of
schizophrenia does not seem to be due
to a change in the prevalence of a seasonal aetiological factor.
Therefore, either there has been a
reduction in incidence due to a change in a non-seasonal agent, or the
incidence of schizophrenia
is not changing and the fall in first admissions is due to confounding
factors.