stable over the 3 years prior to this gene expression analysis (1-year test-retest correlations averaged r = 0.90; intraclass correlation over all 3 years = 0.937, p < 0.0001). Sample selection procedures generated the expected difference in average levels of experienced social isolation (difference in UCLA Loneliness scores, p = 0.0002; Table 1). High-lonely participants did not differ from low-lonely controls on any of the medical or behavioral dimensions analyzed, but they were slightly younger (4 year difference, p = 0.011), had a lower household income (median $45,000 per year versus $87,500, p = 0.010), and reported higher levels of perceived stress (p = 0.023) and depressive symptoms (50% ≥ CEpidemiologic Studies Depression scale (CESD) cut-point of 10 versus 0% of controls, p = 0.038). These demographic and psychological differences were treated as potential confounders in subsequent analyses.
