Sedation associated with quetiapine XR treatment mediated an improvement in agitation [ assessed by the Positive and Negative Syndrome Scale-Excitement ( PANSS-EC ) subscale ] and a worsening in functional capacity [ assessed by the University of California-San Diego ( UCSD ) Performance-Based Skills Assessment-Brief Version ( UPSA-B ) total score ] ; these mediating relationships were not observed for the lurasidone or placebo treatment groups .