Active referral plus a small financial incentive upon cessation services use on smoking abstinence: a community-based, cluster-randomised controlled trial oleh Xue Weng, PhD, Yongda Wu, PhD, Tzu Tsun Luk, PhD, William Ho Cheung Li, PhD, Derek Yee Tak Cheung, PhD, Henry Sau Chai Tong, BBA, Vienna Lai, MPH, Tai Hing Lam, MD, Man Ping Wang, PhD