High levels of psychiatric morbidity in prisoners have been documented in
many countries, but it is not known whether rates of mental illness have
been increasing over time or whether the prevalence differs between
low–middle-income countries compared with high-income ones.
To systematically review prevalence studies for psychotic illness and
major depression in prisoners, provide summary estimates and investigate
sources of heterogeneity between studies using meta-regression.
Studies from 1966 to 2010 were identified using ten bibliographic indexes
and reference lists. Inclusion criteria were unselected prison samples
and that clinical examination or semi-structured instruments were used to
make DSM or ICD diagnoses of the relevant disorders.
We identified 109 samples including 33 588 prisoners in 24 countries.
Data were meta-analysed using random-effects models, and we found a
pooled prevalence of psychosis of 3.6% (95% CI 3.1–4.2) in male prisoners
and 3.9% (95% CI 2.7–5.0) in female prisoners. There were high levels of
heterogeneity, some of which was explained by studies in
low–middle-income countries reporting higher prevalences of psychosis
(5.5%, 95% CI 4.2–6.8; P=0.035 on meta-regression). The
pooled prevalence of major depression was 10.2% (95% CI 8.8–11.7) in male
prisoners and 14.1% (95% CI 10.2–18.1) in female prisoners. The
prevalence of these disorders did not appear to be increasing over time,
apart from depression in the USA (P=0.008).
High levels of psychiatric morbidity are consistently reported in
prisoners from many countries over four decades. Further research is
needed to confirm whether higher rates of mental illness are found in
low- and middle-income nations, and examine trends over time within
nations with large prison populations.