The rates of urine samples that tested negative for opioids did not differ statistically across groups , with 53.8 % ( 95 % CI , 42 % -65 % ) in the referral group , 42.9 % ( 95 % CI , 31 % -55 % ) in the brief intervention group , and 57.6 % ( 95 % CI , 47 % -68 % ) in the buprenorphine group ( P = .17 ) .