referring.. ??

otherdoctors were presented with a choice between two new medications or referral to a specialist.
now only 50 percent went with either of the medications, which means that the percentage of those referring doubled.

referring에 왜 ing를 썼나요 ??ed 써주면 안되나요 ?
정확하고 친절한 답변 부탁드리겠습니다 ^^