Background. Several studies have replicated the finding
increased incidence of schizophrenia and
related psychoses in first and second generation migrants from the Caribbean.
The finding has
remained consistent in studies employing different methods, but concern
been expressed about
indirect methods of calculating the population at risk. This study aims
to overcome these shortcomings.
Method. A further prospective study was undertaken in Nottingham
assembling an inception cohort
of psychotic patients (N=168) presenting from a defined catchment
area. The 1991 census, which
includes codings for self-ascribed ethnic origin, was used to calculate
the denominator, employing
correction factors for potential under-enumeration. Case-ascertainment
based upon all service
contacts and subjects had in-depth assessments including the SCAN. Collateral
history was obtained from informants.
Results. Subjects born in the Caribbean, or who had one or
parents born in the
Caribbean, had a greatly elevated risk (incidence ratios above 7) for all
psychotic disorders and for
ICD-10 (DCR)-defined F20 Schizophrenia.
Conclusions. The size of the increase and the methodological
safeguards employed support the validity
of this now highly replicated finding. A personal or family history of
migration from the Caribbean
is a major risk factor for psychosis; the consistency of this finding justifies
a systematic evaluation of potential aetiological factors. Any hypothesis
derived from the evidence so far must explain:
increased incidence in first and second generation migrants; increased
for all psychoses (including
affective psychoses); and an effect specifically associated with a
migration history from the Caribbean to Northern Europe.