“…A growing body of literature has used the severity–directionality model to examine the development of psychopathology, often in relation to hypothalamic–pituitary–adrenal axis functioning (e.g., Essex et al, 2006; Essex et al, 2011; Luebbe, Elledge, Kiel, & Stoppelbein, 2012; Marceau et al, 2015a; Ruttle, Shirtcliff, Armstrong, Klein, & Essex, 2015; Shirtcliff & Essex, 2008). Severity and directionality scores show stability across adolescence: in a sample of adolescents over-sampled for pure internalizing, pure externalizing, and comorbid internalizing and externalizing problems, Pearson's correlations over two years were r = .74 for severity and r = .56 for directionality (Marceau et al, 2015b).…”