An evaluation of variation in published estimates of schizophrenia prevalence from 1990─2013: a systematic literature review.
BACKGROUND
There is a lack of consistency in findings across studies on the prevalence of schizophrenia, and no recent systematic review of the literature exists. The purpose of this study is to provide an updated systematic review of population-based prevalence estimates and to understand the factors that could account for this variation in prevalence estimates.


METHODS
MEDLINE, Embase, and PsycInfo databases were searched for observational studies describing schizophrenia prevalence in general populations from 2003-2013 and supplemented by studies from a prior review covering 1990-2002. Studies reporting prevalence estimates from specialized populations such as institutionalized, homeless, or incarcerated persons were excluded. Prevalence estimates were compared both across and within studies by factors that might contribute to variability using descriptive statistics.


RESULTS
Sixty-five primary studies were included; thirty-one (48 %) were from Europe and 35 (54 %) were conducted in samples of ≥50,000 persons. Among 21 studies reporting 12-month prevalence, the median estimate was 0.33 % with an interquartile range (IQR) of 0.26 %-0.51 %. The median estimate of lifetime prevalence among 29 studies was 0.48 % (IQR: 0.34 %-0.85 %). Prevalence across studies appeared to vary by study design, geographic region, time of assessment, and study quality scores; associations between study sample size and prevalence were not observed. Within studies, age-adjusted estimates were higher than crude estimates by 17 %-138 %, the use of a broader definition of schizophrenia spectrum disorders compared to schizophrenia increased case identification by 18 %-90 %, identification of cases from inpatient-only settings versus any setting decreased prevalence by 60 %, and no consistent trends were noted by differing diagnostic criteria.


CONCLUSIONS
This review provides updated information on the epidemiology of schizophrenia in general populations, which is vital information for many stakeholders. Study characteristics appear to play an important role in the variation between estimates. Overall, the evidence is still sparse; for many countries no new studies were identified.
Evidera, 430 Bedford Street, Suite 300, Lexington, MA, 02420, USA. jason.simeone@evidera.com.
Jason C
JC
Simeone
Evidera, 430 Bedford Street, Suite 300, Lexington, MA, 02420, USA. alex.ward@evidera.com.
Alexandra J
AJ
Ward
Evidera, 430 Bedford Street, Suite 300, Lexington, MA, 02420, USA. Philip.rotella@evidera.com.
Philip
P
Rotella
Evidera, 430 Bedford Street, Suite 300, Lexington, MA, 02420, USA. jennamcollins@gmail.com.
Jenna
J
Collins
F. Hoffmann-La Roche Ltd, Basel, Switzerland. ricarda.windisch@gmail.com.
Ricarda
R
Windisch
D005060:Europe / Q000453:epidemiology; D006801:Humans; D015995:Prevalence; D012559:Schizophrenia / Q000453:epidemiology*; D013997:Time Factors