Noncontingent participants received vouchers of comparable value independent of smoking status.
Joanna M. Streck, Taylor A. Ochalek, Mollie E. Miller, Andrew C. Meyer, Gary Badger,Charlotte Teneback, Anne Dixon, Stephen T. Higgins, Stacey C. Sigmon 2018, 'Promoting smoking abstinence among patients with chronic obstructive pulmonary disease:Initial feasibility', Preventive medicine reportshttp://www.sciencedirect.com/science/article/pii/S2211335518301128. Retrieved from DOAJ CC BY 4.0 (https://creativecommons.org/licenses/by-sa/4.0/legalcode)