Many conservation programs, such as the Conservation Reserve Program (CRP), use indices to select offers. When modeling how changes in the index weights effect program outcomes, one must account for the attributes of available land, and which landowners chose to participate. This paper introduces a methodology to account for changes in participation as index weights change. Data on the actual CRP (all offers received) are combined with an artificial population of available lands (based on National Resources Inventory data). Bootstrapping methods are used to calibrate estimates of participation probability, and to account for errors-in-variables when estimating how index scores effect this probability. Preliminary analysis suggests that accounting for participation effects will effect estimated impacts of changing the CRP's index weights.