Reliability of the Korean Nottingham Onset Schedule (K-NOS) in Korean First-episode Psychosis Patients

Objective：The duration of untreated psychosis (DUP) has been associated with patient treatment outcome. This study assessed the reliability of the Korean version of the Nottingham Onset Schedule (K-NOS) in assessing DUP among Korean first-episode psychosis patients. Methods：A total of 20 first-episode psychosis patients (mean age=27.1±9.7, range 17−51, males=11) participated in the study. Inter-rater reliability and test-retest reliability were assessed for all subjects using Kappa coefficients and intra-class correlation coefficient (ICC). Five duration criteria of untreated psychosis were determined. Results：The most common prodromal symptoms were irritability, poor mood, sleep changes, and the tendency to avoid people. The most common first psychotic symptoms were auditory hallucination and persecutory delusions. The duration of untreated illness was 332±342 weeks at the time of testing and 336±346 weeks at the time of retesting, and the duration of untreated manifest psychosis was 34±52 weeks at the time of testing and 34±52 weeks at the time of retesting. The duration of untreated emergent psychosis was 78±145 weeks at the time of testing and 77±145 weeks at the time of retesting. Inter-rater reliability of the NOS interview was statistically significant (P-DDx, ICC=0.992, p＜0.001; FPS-DDx, ICC=0.851, p＜0.001; P-T, ICC=0.996, p＜0.001; FBS-T, ICC=0.941, p＜0.001; DDx-T, ICC=0.888, p＜0.001). Test-retest reliability of the NOS interview was also very high (P-DDx, ICC=0.975, p＜0.001; FPS-DDx, ICC=1, p＜0.001; P-T, ICC=0.999, p＜0.001; FBS-T, ICC=0.999, p＜0.001; DDx-T, ICC=1, p＜0.001). Conclusion：The results of this study suggest that the Korean version of Nottingham Onset Schedule measures DUP among Korean first-episode psychosis patients with acceptable reliability.