In stratified analyses , the benefit of sono-electro-magnetic therapy appeared more pronounced among patients who had a symptom duration of 12 months or less ( difference in NIH-CPSI total score -8.3 , 95 % CI -14.5 to 2.6 ) than in patients with a longer symptom duration ( -0.8 , 95 % CI -4.6 to 3.1 ; p for interaction = 0.023 ) .