Our findings replicate the results obtained in clinical populations in Europe and US in a number of ways. We find that the effect of neuroticism on MDD is of a similar magnitude to that reported elsewhere in the world. Typically Western studies estimate the OR of neuroticism to be about 1.5, where the OR reflects the alteration in risk of MDD with each increase of 1 standard deviation in the neuroticism score (Kendler et al., 2006). Our estimate is only slightly less: 1.37. In Western studies, neuroticism has been shown to account for about a third of the comorbidity with internalizing disorders (which include anxiety and depression) (Khan et al., 2005) and to correlate with the severity of depression (indexed by the duration and number of episodes) (Alnaes and Torgersen, 1997; Duggan et al., 1990; Scott et al., 1995). We find that in Chinese patients high neuroticism scores also predispose to higher comorbidity and scores correlate with disease severity. Previous research found that neuroticism accounted for a significant part of the lifetime comorbidity of common psychiatric disorders (internalizing disorders and
