The subjective perception of improvement , measured by an 11-point visual analogue scale , was markedly better in the intervention group ( mean , 8.7 ; standard deviation , 1.0 ; 95 % confidence interval , 8.4-9 .1 ) than in the control group ( mean , 1.4 ; standard deviation , 0.7 ; 95 % confidence interval , 1.2-1 .7 ; t = 33.9 ; P < 0.001 ) .