Significantly more homeless persons receiving permethrin-impregnated underwear than homeless persons receiving the placebo were free of body lice on day 14 in the intent-to-treat population ( 28 % vs 9 % ; P = .04 ) , with a between-group difference of 18.4 percentage points ( 95 % CI , 1.4-35 .4 ) , and in the per-protocol population ( 34 % vs 11 % ; P = .03 ) , with a between-group difference of 23.7 percentage points ( 95 % CI , 3.6-43 .7 ) .