Efficacy of psychological interventions aiming to reduce chronic nightmares: a meta-analysis.

This study presents a meta-analysis of the effectiveness of psychological treatments for chronic nightmares using imaginal confrontation with nightmare contents (ICNC) or imagery rescripting and rehearsal (IRR). Pre-post effect sizes (Hedges' g) were calculated for the outcome measures of nightmare frequency, nights per week with nightmares, sleep quality, depression, anxiety, and PTSD severity. Fixed-effects and random-effects models were applied. High effect sizes were found for nightmare frequency (g=1.04), nights per week with nightmares (g=0.99), and PTSD severity (g=0.92). Most of the effect sizes for the secondary outcomes were moderate. One objective was to clarify whether ICNC or IRR is more important for nightmare reduction. The results indicate that a higher duration of time for ICNC is associated with greater improvements: The minutes of applied ICNC moderate the effect sizes for nightmare frequency at follow-up 2 and for nights per week with nightmares at post and follow-up 1. The percentage of applied ICNC moderates the effect sizes for nightmare frequency and nights per week with nightmares at follow-up 1. Thus, dismantling studies are necessary to draw conclusions regarding whether ICNC or IRR is the most effective in the psychological treatment of chronic nightmares.