Figure 2From: Air ions and mood outcomes: a review and meta-analysis Low-Density Negative Air Ion Exposure and Depression. *Includes data from studies at the last follow-up time point where applicable [6–8]; p for heterogeneity (composite SIGH-SAD) < 0.0001. CI: Confidence Interval; SIGH-SAD: Structured Interview Guide for the Hamilton Depression Rating Scale, Seasonal Affective Disorders.Back to article page