title: Birth seasonality in schizophrenia: effects of gender and income status.
abstract: OBJECTIVE
  The aim of this study was to examine the correlations of birth seasonality in schizophrenia, considering influences of gender and income status.
  
  
  METHODS
  The sample consisted of 1 000 000 people in the general population randomly selected from the Taiwan National Health Insurance Research Database. Data for the birth-year period 1950-1989 were extracted for analysis (n = 631 911; 306 194 male, 325 717 female). Subjects with schizophrenia (2796 male, 2251 female) were compared with the general population. Subgroups divided by birth-year periods (10-year interval), gender, and income status (low, medium, high) were analyzed using both the Walter and Elwood seasonality and chi-squared tests.
  
  
  RESULTS
  The winter/spring birth excess in schizophrenia was 5.3% when compared with the general population. There was a statistically significant excess in winter/spring births than summer/autumn births inschizophrenia patients (relative risk [RR], 1.12; 95% confidence interval [CI]: 1.06-1.18). This winter/spring birth excess in schizophrenia was observed only in female subjects (RR, 1.20; 95%CI: 1.10-1.30), not in male subjects (RR, 1.03; 95%CI: 0.98-1.14), in all subgroups of income status, but was most pronounced in the low income subgroup (RR, 1.20, 1.09, 1.13; 95% CI: 1.05-1.37, 1.01-1.17, 1.02-1.25 for low, medium, and high income status, respectively).
  
  
  CONCLUSIONS
  A gender difference with female predominance of the effect of birth seasonality in schizophrenia, and a more pronounced effect in low income status were noted.
authors.affiliation: Department of Public Health and Primary Care, School of Clinical Medicine, University of Cambridge, Cambridge, UK.
authors.forename: Chin
authors.initials: C
authors.lastname: Cheng
authors.forename: El-Wui
authors.initials: el-W
authors.lastname: Loh
authors.forename: Ching-Heng
authors.initials: CH
authors.lastname: Lin
authors.forename: Chin-Hong
authors.initials: CH
authors.lastname: Chan
authors.forename: Tsuo-Hung
authors.initials: TH
authors.lastname: Lan
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D016001:Confidence Intervals; D003627:Data Interpretation, Statistical; D016208:Databases, Factual; D005260:Female; D006801:Humans; D007182:Income; D007348:Insurance, Health / Q000706:statistics & numerical data; D008297:Male; D008875:Middle Aged; D012559:Schizophrenia / Q000453:epidemiology*; D012621:Seasons; D012737:Sex Factors; D013624:Taiwan / Q000453:epidemiology
keywords: epidemiology; schizophrenia; season of birth; seasonality