Intention-to-treat analysis found lower Neck Disability Index scores at 6 months in the mechanical traction group compared to the exercise group ( mean difference between groups , 13.3 ; 95 % confidence interval : 5.6 , 21.0 ) and over-door traction group ( mean difference between groups , 8.1 ; 95 % confidence interval : 0.8 , 15.3 ) , and at 12 months in the mechanical traction group compared to the exercise group ( mean difference between groups , 9.8 ; 95 % confidence interval : 0.2 , 19.4 ) .