title: [Analysis of the seasonality of birth effect in schizophrenic patients in Poland with the application of the seasonal decomposition method].
abstract: BACKGROUND
  Seasonality of the birth of patients diagnosed with schizophrenia is one of the most repetitive phenomena in epidemiological studies on this illness. The paper presents a review of the literature, with an emphasis on the research findings and development of methods used to investigate the phenomenon.
  
  
  OBJECTIVE
  The aim of the study was to analyze the phenomenon of birth seasonality in schizophrenic patients in the Polish population, using new methods of the seasonal decomposition analysis.
  
  
  METHODS
  The study utilized birth dates of 13,668 patients diagnosed with schizophrenia according to the ICD-10 criteria, and discharged from all psychiatric hospitals in Poland in the years 1997-2000. The data on live births in the general population as published by the Main Statistical Office served as the reference group. 7,432,803 people were born in Poland in the years 1964-1976. Efforts were made to minimize the age-related incidence effect. In order to eliminate seasonal variations resulting from deviations in the number of births in the general population, an indicator of the number of births of patients diagnosed with schizophrenia per 10 thousand live births in the general population was created. A time series of 156 monthly observations covering the period of 13 years was produced. The data were analyzed using the Census II X- 11 method, one of the most recent methods to analyze time series and seasonal decomposition.
  
  
  RESULTS
  The results confirm a 5-8% birth excess for schizophrenia in December and January.
authors.affiliation: Klinika Psychiatrii, Instytut Psychiatrii i Neurologii w Warszawie.
authors.forename: Andrzej
authors.initials: A
authors.lastname: Bembenek
mesh_terms: D000293:Adolescent; D000328:Adult; D001719:Birth Certificates; D016009:Chi-Square Distribution; D002648:Child; D002980:Climate; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D011044:Poland / Q000453:epidemiology; D011157:Population Dynamics; D012307:Risk Factors; D012559:Schizophrenia / Q000175:diagnosis* / Q000453:epidemiology*; D012565:Schizophrenic Psychology; D012621:Seasons