The mean improvement in peak flow of the experimental and control groups was 37.5 ( 95 % confidence interval ( CI ) 26.7-48 .2 ) l/min and 38.7 ( 95 % CI , 26.1-51 .3 ) l/min , respectively , with a mean difference of 1.3 ( 95 % CI , -15.1 to 17.7 ) l/min .