Voluntary measures have traditionally been evaluated using a similar framework regardless of their structure. The framework assumes that the measure provides partners with a treatment (information, research support, etc.) that will not be transferred to non-partners. In this framework, a voluntary measure is said to be worthwhile if differences are significant between the behavior of partners and non-partners, correcting for the potential endogeneity of becoming a partner. However, voluntary measures take many different forms, some which are expected to have transfers to non-partners (spillovers). The Coal Combustion Products Partnership (C2P2) is a U.S. voluntary program with a structure that is likely to provide treatment spillovers to non-partners. This paper evaluates C2P2 and tests whether treatment spillovers are affecting non-partners' behavior. Results are consistent with a program that would traditionally be considered unsuccessful, but the consideration of treatment spillovers makes it consistent with a successful program.
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