ERN1 and post-traumatic stress disorder: Comparing across groups using Fisher’s z-transformation, the correlation between IL-18 and IRE1 is significantly stronger in Past PTSD > 5y (ρ = 0.879) than in No PTSD (ρ = 0.409), with z = 2.87 (p = 0.004, two-tailed), demonstrating that PTSD enhances the coupling of inflammatory and stress pathways.