Psychometric properties of the Disturbing Dream and Nightmare Severity Index - Korean version.

STUDY OBJECTIVES This study aimed to examine psychometric properties of the Disturbing Dream and Nightmare Severity Index (DDNSI) in individuals aged between 18 and 39. METHODS All participants (n=674) were asked to complete the DDNSI, including the modified Nightmare Effects Survey (mNES). Additionally, 109 participants were tested for test-retest reliability after three months. Among our sample, 229 (33.9%) reported having at least one nightmare per month. RESULTS Internal consistency was evaluated for the total sample (Cronbach's α = .920) and separately for individuals reporting more than once per month (Cronbach's α = .755). Test-retest reliability after three months was .705. Convergent validity of the DDNSI with mNES was also satisfactory (r = .638, p < .001). Finally, exploratory factor analysis was conducted to explore the construct of the DDNSI, and results indicated that it consisted of two factors, nightmare frequency and nightmare distress [χ²(df) = 2.241(1) △χ² (△df) = 155.575(4), TLI = .980, RMSEA (90% CI) = .074 (0, .208), SRMR = .011]. CONCLUSIONS The DDNSI is a reliable measure of nightmare severity that can be used in various settings.