iPST participants displayed a significantly greater reduction in depressive symptoms after the intervention ( d = 0.59 , 95 % CI 0.26-0 .92 ) , after three months ( d = 0.37 , 95 % CI 0.05-0 .70 ) and after six months ( d = 0.38 , 95 % CI 0.05-0 .70 ) compared to the control group .