Introduction: Comorbid depressive symptoms (depression thereafter) often occur in schizophrenia and are associated with negative outcomes. This meta-analysis estimated the prevalence of comorbid depression and its associated factors in schizophrenia. Methods: Both international (PubMed, EMBASE, PsycINFO, and Web of Science) and Chinese (WANFANG and CNKI) databases were systematically searched. Studies with data on the prevalence of comorbid depression in schizophrenia measured with the Calgary Depression Scale for Schizophrenia (CDSS) were included. Randomeffects models were used in all analyses. Results: Fifty-three studies covering 9,879 patients were included. The pooled prevalence of comorbid depression was 28.6% (95%CI: 25.3%-32.2%). Subgroup analyses revealed that studies examining inpatients, being published in Chinese language, or those with lower CDSS cut-od values reported higher depression rates. Metaregression analyses indicated that the rate of depression was positively associated with publication year, proportion of males, mean age, and severity of psychotic symptoms, and negatively associated with illness duration and study quality. Conclusion: Comorbid depression is common in schizophrenia. Due to its negative impact on patients’ quality of life and prognosis, regular screening and effective treatment for comorbid depression should be implemented in patients with schizophrenia.
Comorbid depressive symptoms (depression thereafter) are present in all phases of schizophrenia (Naguy, 2018; Upthegrove, 2009) and correlated with higher risk of suicide (Ayesa-Arriola et al., 2015; Bagaric et al., 2013; Li et al., 2018), polypharmacy (Lako et al., 2012b), worse psychosocial functioning (Schennach‐Wolff et al., 2011), and poorer quality of life (Alessandrini et al., 2016; Sim et al., 2004), and functional outcomes (Conley et al., 2007). Because comorbid depression is often under-diagnosed in schizophrenia, patients may not receive appropriate treatment (Lako et al., 2012b; Majadas et al., 2012; Upthegrove et al., 2017). Elucidating the pattern of comorbid depression and its correlates in schizophrenia could benefit the management and prognosis of affected patients. The prevalence of comorbid depression varies greatly across studies; for instance, one study (Dai et al., 2018) found the rate of depression measured with the 17-item Hamilton Depression Rating Scale (HAMD-17) in schizophrenia inpatients was 54.6%, while the corresponding figures were 12.9% when using the Present State Examination (PSE) (Barnes et al., 1989) and 31% in outpatients with the Calgary Depression Scale for Schizophrenia (CDSS) (Majadas et al., 2012). Discrepancies between these studies could be partially due to different study settings, the severity of psychotic symptoms, and assessment instruments. Several scales have been used to assess comorbid depression in schizophrenia including generic ones, such as the HAMD and PSE, that have not been validated in schizophrenia and they are not as sensitive as schizophrenia-specific measures, such as the CDSS. The 9-item CDSS was developed to identify comorbid depression in schizophrenia; its total score ranges from 9 to 27 with a higher total score indicating more severe depression. The CDSS has satisfactory psychometric properties and has been widely used (Lako et al., 2012a; Scholes and Martin, 2013). Different CDSS cutoff values have been applied in research and clinical practice: a total score of ≥۵ (Hani et al., 2016), ≥۶ (Chang et al., 2015), ≥۷ (Fountoulakis et al., 2017), >7 (Thomas et al., 2014), or ≥۱۲ (Üçok et al., 2013).