Fig. 2From: Objective and subjective measures of sleep initiation are differentially associated with DNA methylation in adolescentsCorrelation matrix among sleep initiation measures. The correlation matrix displays the relationships among the different measures of sleep initiation. These measures include bedtime, SOL, and SOT measured by self-report, ACT, and PSG. The color and size of each circle represent the correlation coefficient. The p-value for each correlation is indicated in the matrix: *p < 0.05, **p < 0.01,***p < 0.001Back to article page