We use propensity score matching to estimate additionality from enrollment in federal costshare programs for six practices. We analyze farmer adoption decisions based on farmer survey data in Ohio. We develop a new methodological approach to decompose the average treatment effect on the treated according to relative contributions of voluntary adopters and new adopters. Our results indicate that cost-share programs achieve positive levels of additionality for each practice. But percent additionality varies dramatically between practices. Specifically, percent additionality is highest for hayfield establishment (93.3%), cover crops (90.6%), and filter strips (88.9%), while it is lowest for conservation tillage (19.3%). (JEL Q24, Q28). © 2013 by the Board of Regents of the University of Wisconsin System.