Figure 1From: Air ions and mood outcomes: a review and meta-analysis High-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) = 0.94. CI: Confidence Interval; SIGH-SAD: Structured Interview Guide for the Hamilton Depression Rating Scale, Seasonal Affective Disorders.Back to article page