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Objective: The aim of the present study was to compare two versions of the Kessler 10-item scale (K10), as measures of population mental health status in New Zealand., Method: A nationwide household survey of residents aged > or = 16 years was carried out between 2003 and 2004. The World Mental Health Composite International Diagnostic Interview (CIDI 3.0) was used to obtain DSM-IV diagnoses. Serious mental illness (SMI) was defined as for the World Mental Health Surveys Initiative and the USA National Comorbidity Survey Replication. Participants were randomly assigned to receive the 'past month' K10 or the 'worst month in the past 12 months' K10. There were 12 992 completed interviews; 7435 included the K10. The overall response rate was 73.3%. Receiver operator characteristic (ROC) curves were used to examine the ability of both K10 versions to discriminate between CIDI 3.0 cases and non-cases, and to predict SMI., Results: Scores on both versions of the K10 were higher for female subjects, younger people, people with fewer educational qualifications, people with lower household income and people resident in more socioeconomically deprived areas. Both versions of the K10 were effective in discriminating between CIDI 3.0 cases and non-cases for anxiety disorder, mood disorders and any study disorder. The worst month in the past 12 months K10 is a more effective predictor than the past 1 month K10 of SMI (area under the curve: 0.89 vs 0.80)., Conclusions: Either version of the K10 could be used in repeated health surveys to monitor the mental health status of the New Zealand population and to derive proxy prevalence estimates for SMI. The worst month in the past 12 months K10 may be the preferred version in such surveys, because it is a better predictor of SMI than the past month K10 and also has a more logical relationship to 12 month disorder and 12 month service use.

Objective: To estimate the lifetime prevalence and projected lifetime risk at age 75 years of DSM-IV disorders in New Zealand., Method: A nationwide face-to-face household survey carried out in 2003-2004. A fully structured diagnostic interview, the World Health Organization Composite International Diagnostic Interview (CIDI 3.0), was used. There were 12,992 completed interviews from participants aged 16 years and over. The overall response rate was 73.3%. In this paper, the outcomes reported are lifetime prevalence and projected lifetime risk at age 75 years., Results: The lifetime prevalence of any disorder was 39.5%. The lifetime prevalences for disorder groups were: anxiety disorders, 24.9%; mood disorders, 20.2%; substance use disorders, 12.3%; and eating disorders, 1.7%. The prevalences for all disorders were higher in the younger age groups. Females had higher prevalences of anxiety, mood and eating disorders compared with males; males had higher prevalences of substance use disorders. The estimated projected lifetime risk of any disorder at age 75 years was 46.6% with the median age of onset being 18 years. Adjustment for age, sex, education and household income did not remove all differences between Māori and the composite other ethnic group in the risk of disorder (hazard ratio = 1.1-1.4). After adjustment, hazard ratios for Pacific people ranged from 0.8 to 2.5., Conclusions: These results confirm those of other studies: mental disorders are relatively common and tend to have early onset. Females are more likely to experience anxiety, mood and eating disorders than males, who experience more substance use disorders. Adjustment for socioeconomic factors and demography does not explain all ethnic differences, although remaining differences are small relative to cohort and even sex differences.