Least squares mean differences ( 95 % CI ) were statistically significant for vilazodone versus placebo on MADRS ( -5.117 [ -6.886 to -3.347 ] , P < .00001 ) and CGI-S ( -0.622 [ -0.845 to -0.399 ] , P < .00001 ) change from baseline ; statistically significant improvements versus placebo occurred at week 2 and persisted for the study duration .