BDNF and depressive disorder: Chi square tests for independence indicated no significant association between BDNF rs6265 alleles and depression (considered non-significant if p > 0.05): Wave 1, χ2 (2, 1337) = 0.725, p = 0.7, and phi = 0.02; wave 2, χ2 (2, 1269) = 2.01, p = 0.33, and phi = 0.42; wave 3, χ2 (2, 890) = 4.58, p = 0.1, and phi = 0.07.