In both studies , there were significant improvements in the primary end point in both lumacaftor-ivacaftor dose groups ; the difference between active treatment and placebo with respect to the mean absolute improvement in the percentage of predicted FEV1 ranged from 2.6 to 4.0 percentage points ( P < 0.001 ) , which corresponded to a mean relative treatment difference of 4.3 to 6.7 % ( P < 0.001 ) .