Actor–partner interdependence model analyses regressing adolescent and young adult (AYA) patients' and caregivers' perceptions of subjective illness severity on posttraumatic stress symptoms (PTSS) (n= 110 dyads). Baseline model shown with standardized estimates and standard errors. Paths a and d: within-person effects. Paths b and c: crossover effects. R2: variance in AYA patients' and caregivers' PTSS explained by the model. Ninety-five percent CIs: path a [0.09, 0.21], path b [0.03, 0.25], path c [−0.04, 0.09], and path d [0.04, 0.26]. Standard errors of estimate: path a (0.03), path b (0.06), path c (0.03), and path d (0.06). *p < 0.05; **p < 0.01; ***p < 0.001