We also compared perforin expression in the NK cells of depressed hip fracture patients with and without depressive symptoms 6 weeks and 6 months post-surgery, but there was no significant effect of time, F(1, 13) = .27, p = 0.61, η2 = .021 (Fig. 6b) such that perforin expression in NK cells did not improve even 6 months post-injury in depressed hip fracture patients. This evidence concerns the gene PRF1 and hip fracture.