Spss software was used to conduct the analysis. Descriptive statistics were obtained for all variable, incliuding distributions, mean, medians, variances and standard deviations. Comparisons between cases and controls used Chi square test, Fisher's exact test ( for nominal data) or t-test (for continuous variables). Because of the large number of univariate analyses, we subjected the data to futher analyses using the False Discovery rate method. All analyses used a two-tailed alpha(p=0.05) as the level of statistical significance.
This study was approved by the institutional review boards of the Beijing Hui Long Guan Hospital and the Chinese academy of preventive medicine.
Table 1 summarizes subjects' characteristics. There were no differences between cases and controls in age, gender or rural versus urban residence. Compared to individuals with schizophrenia who died by accident, those who died by suicide were more likely to have had a greater mean effect of negative life events in the prior year-despite having a similar number of chronic and acute negative life events. There were no differences between the groups in the age of onset of schizophrenia, in the proportion who had a positive family history for psychosis or depression or in the proportion who had been treated with antipsychotics or antidepressants in the month before death.
Furthermore, there were no differences between the groups in terms of the severity of illness in the month before death or whether they had prior mental health treatment.
Table2 compares the prevalence of different psychotic and depressive symptoms between the two groups. There were no differences between the groups in the prevalence of different psychotic symptoms over the month prior to death. In addition, none of the accidental controls met DSM-IV criteria for major or minor depression while 20 of 74 suicide decedents met full criteria for DSM-IV major or minor depression; this difference was statistically significant. Furthermore, the group that completed suicide were more likely to have had a past suicide attempt, to have recently experienced the symptoms and the effect of the depressive symptoms on functioning were significantly higher in those who died by suicide.